What can high-carotenoid foods do for you?

• Protect your cells from the damaging effects of free radicals
• Provide a source of vitamin A
• Enhance the functioning of your immune system
• Help your reproductive system function properly

What events and lifestyle factors can indicate a need for more high-carotenoid foods?

• Smoking and regular alcohol consumption
• Low intake of fruits and vegetables

Food sources of carotenoids include carrots, sweet potatoes, spinach, kale, collard greens, and tomatoes. To maximize the availability of the carotenoids in the foods listed above, the foods should be eaten raw or steamed lightly.

What are carotenoids?

Carotenoids represent one of the most widespread groups of naturally occurring pigments. These compounds are largely responsible for the red, yellow, and orange color of fruits and vegetables, and are also found in many dark green vegetables. The most abundant carotenoids in the North American diet are beta-carotene, alpha-carotene, gamma-carotene, lycopene, lutein, beta-crpytoxanthin, zeaxanthin, and astaxanthin.

How it Functions

What are the functions of carotenoids?

Preventing Vitamin A Deficiency

Until late in the 20th Century, the functions of carotenoids were discussed only in terms of their potential vitamin A activity. Certain members of the carotenoid family, approximately 50 carotenoids of the known 600, are called "provitamin A" compounds because the body can convert them into retinol, an active form of vitamin A.

As a result, foods that contain carotenoids can help prevent vitamin A deficiency. The most commonly consumed provitamin A carotenoids are beta-carotene, alpha-carotene, and beta-cryptoxanthin, but gamma-carotene and beta-zeacarotene also have provitamin A activity.

Antioxidant & Immune-Enhancing Activity

In recent years, carotenoids have received a tremendous amount of attention as potential anti-cancer and anti-aging compounds. Carotenoids are powerful antioxidants, protecting the cells of the body from damage caused by free radicals. Carotenoids, and specifically beta-carotene, are also believed to enhance the function of the immune system.

Promoting Proper Cell Communication

In addition to their antioxidant and immune-enhancing activity, carotenoids have shown the ability to stimulate cell to cell communication. Researchers now believe that poor communication between cells may be one of the causes of the overgrowth of cells, a condition which eventually leads to cancer. By promoting proper communication between cells, carotenoids may play a role in cancer prevention.

It is also believed that carotenoids participate in female reproduction. Although the exact function of carotenoids in female reproduction has not yet been identified, it is known that the corpus luteum has the highest concentration of beta-carotene of any organ in the body, suggesting that this nutrient plays an important role in reproductive processes.

Deficiency Symptoms

What are deficiency symptoms for carotenoids?

A low dietary intake of carotenoids is not known to directly cause any diseases or health conditions, at least in the short term. However, if your intake of vitamin A is also low, a dietary deficiency of the provitamin A carotenoids (beta-carotene, alpha-carotene, and beta-cryptoxanthin) can cause the symptoms associated with vitamin A deficiency.

In addition, long-term inadequate intake of carotenoids is associated with chronic disease, including heart disease and various cancers. One important mechanism for this carotenoid-disease relationship appears to be free radicals. Research indicates that diets low in carotenoids can increase the body’s susceptibility to damage from free radicals. As a result, over the long term, carotenoid-deficient diets may increase tissue damage from free radical activity, and increase risk of chronic diseases like heart disease and cancers.

Due to low consumption of fruits and vegetables, many adolescents and young adults do not take in enough carotenoids. In addition, if you smoke cigarettes and/or drink alcohol, you may have lower than normal blood levels of carotenoids. Statistically speaking, smokers and drinkers eat fewer foods that contain carotenoids. Also, researchers suspect that cigarette smoke destroys carotenoids. However, if you do smoke or drink, use carotenoid supplements with caution (see Toxicity section).

Toxicity Symptoms

What are toxicity symptoms for carotenes?

A tell-tale sign of excessive consumption of beta-carotene is a yellowish discoloration of the skin, most often occurring in the palms of the hands and soles of the feet. This condition is called carotenodermia, and is reversible and harmless. Excessive consumption of lycopene can cause a deep orange discoloration of the skin. Like carotenodermia, lycopenodermia is harmless.

High intake of carotenoid-containing foods or supplements is not associated with any toxic side effects. As a result, the Institute of Medicine at the National Academy of Sciences did not establish a Tolerable Upper Intake Level (UL) for carotenoids when it reviewed these compounds in 2000.

However, the results of two research studies indicate that those who smoke heavily and drink alcohol regularly, may increase their chance of developing lung cancer and/or heart disease if they take beta-carotene supplements in amounts greater than 20-30 milligrams per day.

Impact of Cooking, Storage and Processing

How do cooking, storage, or processing affect carotenoids?

In certain cases, cooking can improve the availability of carotenoids in foods. For example, the availability of lycopene from tomato products is increased when the foods are processed at high temperatures. As a result, your body absorbs the lycopene in canned, pasteurized tomato juice more easily than the lycopene in a fresh tomato. In addition, lightly steaming carrots and spinach improves your body’s ability to absorb the carotenoids in these foods.

It is important to note, however, that in most cases, prolonged cooking of vegetables decreases the availability of carotenoids by changing the shape of the carotenoid from its natural trans-configuration to a cis-configuration. For example, fresh carrots contain 100% all-trans beta-carotene, while canned carrots contain only 73% all-trans beta-carotene.

Factors that Affect Function

What factors might contribute to a deficiency of carotenoids?

Carotenoids are fat-soluble substances, and as such require the presence of dietary fat for proper absorption through the digestive tract. Consequently, your carotenoid status may be impaired by a diet that is extremely low in fat or if you have a medical condition that causes a reduction in the ability to absorb dietary fat such as pancreatic enzyme deficiency, Crohn’s disease, celiac sprue, cystic fibrosis, surgical removal of part or all of the stomach, gall bladder disease, and liver disease.

Drug-Nutrient Interactions

What medications affect carotenoids?

The cholesterol-lowering medications referred to as bile acid sequestrants (Cholestyramine, Colestipol, and Colestid) lower blood levels of carotenoids. In addition, margarines enriched with plant sterols such as Benecol and Take Control, may decrease the absorption of carotenoids. Olestra, a fat substitute added to snack foods, may also decrease the absorption of carotenoids.

Nutrient Interactions

How do other nutrients interact with carotenoids?

Beta-carotene supplements reduce blood levels of lutein, suggesting that carotenoids may compete with each other for absorption.

Supplementing your diet with pectin may decrease the absorption of carotenoids.

Health Conditions

What health conditions require special emphasis on carotenoids?

Carotenoids may play a role in the prevention and/or treatment of the following health conditions:

• Acquired Immunodeficiency Syndrome (AIDS)
• Age-related macular degeneration
• Angina pectoris
• Asthma
• Cataracts
• Cervical cancer
• Cervical dysplasia
• Chlamydial infection
• Heart disease
• Laryngeal cancer (cancer of the larynx)
• Lung cancer
• Male and female infertility
• Osteoarthritis
• Photosensitivity
• Pneumonia
• Prostate cancer
• Rheumatoid arthritis
• Skin cancer
• Vaginal candidiasis

What forms of carotenoids are found in dietary supplements?

In dietary supplements, carotenoids are available as synthetic all-trans beta-carotene, beta- and alpha-carotene from the algae Dunaliella, and mixed carotenes from palm oil.

It is important to note, however, that, due to the inconsistent results from research studies aimed at evaluating the health benefits of beta-carotene supplements, the National Academy of Sciences cautions against taking high dose carotenoid supplements, except as a method for preventing vitamin A deficiency.

Food Sources

Introduction to Nutrient Rating System Chart

The following chart shows the foods which are either excellent, very good or good sources of this nutrient. Next to each food name you will find the following information: the serving size of the food; the number of calories in one serving; DV% (percent daily value) of the nutrient contained in one serving (similar to other information presented in the website, this DV is calculated for 25-50 year old healthy woman); the nutrient density rating; and the food's World's Healthiest Foods Rating. Underneath the chart is a table that summarizes how the ratings were devised. For more detailed information on our Nutrient Rating System, please click here.

What are current public health recommendations for carotenoids?

To date, no recommended dietary intake levels have been established for carotenoids. In an effort to set such recommendations, the Institute of Medicine at the National Academy of Sciences reviewed the existing scientific research on carotenoids in 2000.

Despite the large body of population-based research that links high consumption of foods containing beta-carotene and other carotenoids with a reduced risk of several chronic diseases, the Institute of Medicine concluded that this evidence was not strong enough to support a required carotenoid intake level because it is not yet known if the health benefits associated with carotenoid-containing foods are due to the carotenoids or to some other substance in the food.

However, the National Academy of Sciences supports the recommendations of various health agencies, which encourage individuals to consume five or more servings of fruits and vegetable every day. This level of intake of fruits and vegetables provides approximately three to six milligrams of beta-carotene.

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http://ibscrohns.about.com/library/fda/blvita5.htm

Facts About Vitamin A and Carotenoids

Selected Food Sources of vitamin A

     As the 2000 Dietary Guidelines for Americans state, "Different foods contain different nutrients. No single food can supply all the nutrients in the amounts you need" (41). The following tables suggest dietary sources of vitamin A and provitamin A carotenoids. As the tables indicate, liver, eggs and whole milk are good animal sources of vitamin A. Many orange fruits and green vegetables are good sources of provitamin A carotenoids. Including these foods in your daily diet will help you meet your daily need for vitamin A. In addition, food manufacturers fortify a wide range of products with vitamin A. Breakfast cereals, pastries, breads, crackers, cereal grain bars and other foods may be fortified with 10% to 15% of the DV for vitamin A. It is important to read the nutrition facts panel of the food label to determine whether a food provides vitamin A.

http://www.vitacost.com/science/hn/Supp/Carotenes.htm

Carotenoids have been used in connection with the following conditions (refer to the individual health concern for complete information):

Rating	Health Concerns
	Cataracts (prevention) Heart disease (prevention) Macular degeneration (prevention) (lutein, zeaxanthin, lycopene) Sickle cell anemia
Reliable and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit. An herb is primarily supported by traditional use, or the herb or supplement has little scientific support and/or minimal health benefit.

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http://sarasota.extension.ufl.edu/FCS/nwslttr/Apr04/Article6Vitamin-A.htm

Facts About Vitamin A

Why do we need vitamin A?

Vitamin A is a fat-soluble vitamin that is essential to our health.  It helps you see normally in the dark.  Vitamin A also promotes normal growth and health of body cells, and keeps skin healthy.

There are animal sources (retinol) and vegetable sources (carotenoids) of vitamin A in foods.  Only a few of the carotenoids in foods are converted to vitamin A in the body.  Beta-carotene is the most familiar carotenoid.

Beta-carotene, and several other carotenoids, act as antioxidants.  Antioxidants help slow down or prevent cell damage.  By protecting cells from damage, antioxidants may reduce risk for certain cancers and heart disease.

What happens if we don’t get enough vitamin A?

Inadequate intake of vitamin A can cause night blindness, dry scaly skin, increased risk for infections, and poor growth.

How much vitamin A do we need?

The following table lists recommended daily intakes of vitamin A:

Recommended intakes for vitamin A are given as “Retinol Activity Equivalents.  This helps to account for the differences between carotenoids and retinol.  It takes about 12 units of beta-carotene and 24 units of other carotenoids to make 1 unit of retinol in the body.

How can we get enough vitamin A?

We get vitamin A by eating a variety of fruits and vegetables that contain carotenoids, and from dairy products fortified with vitamin A.  Vitamin A is also found in liver and egg yolks.

Here are some food sources of vitamin A and carotenoids:

What about supplements?

We don’t need supplements since vitamin A is so widely available in foods and easily stored in the body.  Pregnant women especially should avoid taking retinol supplements.  High doses during pregnancy can cause birth defects.  Look for beta-carotene as the vitamin A source in prenatal supplements.

How much is too much?

Taking large doses of retinol can cause severe health problems.  These include vomiting, bone and joint pain, dry scaly skin, and liver damage.  Vitamin A toxicity can kill you!  Keep your total vitamin A intake less than 3,000 ug/day from retinol.

Where can I get more information?

The Family and Consumer Sciences (FCS) agent at your county Extension office may have written information and nutrition classes for you to attend.  Also, a registered dietitian (RD) can provide reliable information to you.  Reliable nutrition information may be found on the internet at the following sites:  http;//www.nutrition.gov and  http//www.eatright.org .

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http://www.md-phc.com/nutrition/carotenoids_and_human_health.htm

Carotenoids and Human Health

i.e. Eat your fruits and vegetables!

  What are Carotenoids?

Carotenoids are red, yellow and orange pigments, which are widely distributed in nature and are especially abundant in yellow-orange fruits and vegetables and dark green leafy vegetables. They serve many functions. In plant life they are essential for photosynthesis. They also play a major role in the photoprotection of cells and tissues by neutralizing oxidants. Since a large part of the aging process is felt to be due to oxidation, carotenoids are, therefore, important.

  Role in Human Health

The knowledge of the importance of carotenoids in human health is not new. For years it has been known that beta-Carotene plays an essential role as the main dietary source of vitamin A. Deficiency of vitamin A, particularly in the third world countries, accounts for blindness in 250,000 to 500,000 children a year according to estimates by the World Health Organization. More recently, protective effects of carotenoids against serious disorders such as heart disease, cancer and degenerative eye disease have been recognized stimulating intensive research into the role of carotenoids as antioxidants and possibly as regulators of the immune system.

Thus far there have been over 700 naturally occurring carotenoids identified and as many as 50 may be absorbed and metabolized by the human body. Of these, 14 carotenoids have be identified in the human serum. Common carotenoids include Lutein, Zeathanthin, Lycopene, beta-Carotene and alpha-Carotene.

Lutein and Zeathanthin

Lutein and Zeathanthin are found in the retina and compose the macular pigment. They function to protect photoreceptor cells from light-generated oxidants known as free radicals. Because of this they play a key role in the protection of a common form of blindness known as age-related macular degeneration (ARMD). Studies have been conducted demonstrating that the levels of both Lutein and Zeathanthin in the retina can been enhanced with foods rich in these compounds and that these levels correlate inversely with the incidence of ARMD. Dietary sources include kale, mustard greens, spinach, corn, celery, broccoli, lettuce, parsley and green peas. 

Importantly, Lutein has recently been shown to be very important in the prevention of heart disease!

Lycopene

Lycopene is the carotenoid that imparts the red and pink colors to many of the fruits and vegetables we eat. It like the other carotenoids is a powerful antioxidant and displays chemoprotective properties. Serum levels have been inversely related to the risk of pancreatic, cervical and prostate cancer. More recently, serum levels have been shown to be inversely related to the risk of heart disease as well. Dietary sources of lycopene include tomatoes and tomato products, apricots, pink grapefruit, guava, skin of red grapes, papaya and watermelon.

beta-Carotene

beta-Carotene provides the major source of vitamin A in the body. Serum levels correlate inversely with a variety of cancers and deficiency is associated with blindness particularly in third world countries. beta-Carotene exhibits potent antioxidant activity and can be found in carrots, pumpkin, papaya, peaches prunes, squash, sweet potato, apricots, cabbage, lima beans, green beans, broccoli, brussel spouts, kale, kiwi, lettuce, peas, spinach, tomatoes, pink grapefruit, honeydew melon and oranges.

alpha-Carotene

alpha-Carotene is similar to beta-Carotene in its biologic activity with the exception that it is a more potent antioxidant and smaller amounts are converted to vitamin A. Serum levels are generally between 10 and 20% of beta-Carotene levels and like beta-Carotene are inversely associated with cancer. Dietary sources are much the same as for beta-Carotene.

 Effects of preparation and differences in absorption

Cooking: Cooking reduces the carotenoid content of food, but also disrupts cellular membranes and liberates nutrients. Carotenoids are, therefore, absorbed more efficiently from cooked versus uncooked foods.

Drying: Since dried fruits contain little water, they are by weight much higher in carotenoids than fresh fruit.

Processing: Processing food as in tomato juice releases nutrients as well. The lycopene content on a weight basis in tomato juice is over twice the content of raw tomatoes.

Supplements versus purified sources: Serum levels of beta-carotene were almost 20% higher in persons who consumed purified beta-carotene in a capsule compared to those ingesting an equivalent amount from cooked carrots.

  Summary

In summary, the two epidemics in America today, heart disease and cancer, are to a large degree nutritionally related. Americans today are consuming less fruits, vegetables and whole grains than at any other time in history. It is my sincere hope that an increase in public awareness of the importance of proper nutrition will lead to changes in dietary habits that will have a significant positive impact on the health of all Americans. Now….eat your fruits and vegetables!

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Vitamin A and Carotenoids

Vitamin A: What is it?

What foods provide vitamin A?

What is the Recommended Dietary Allowance
for vitamin A?

Table 1: Recommended Dietary Allowances for vitamin A for children and adults

Table 2: Adequate Intake for vitamin A for infants

When can vitamin A deficiency occur?

• Signs of vitamin A deficiency
  
• Who may need extra vitamin A to prevent a deficiency?

What is the association between vitamin A, beta carotene, and cancer?

Can an excess intake of vitamin A promote osteoporosis?

What is the health risk of too much vitamin A?

Table 3: Tolerable Upper Intake Levels for preformed vitamin A for children and adults

What is the health risk of too many carotenoids?

Selected food sources of vitamin A

• Table 4: Selected animal sources of vitamin A
  
• Table 5: Selected plant sources of vitamin A

References

Printable pdf version

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Vitamin A: What is it?

Vitamin A is a family of fat-soluble vitamins. Retinol is one of the most active, or usable, forms of vitamin A, and is found in animal foods such as liver and eggs and in some fortified food products.

Retinol is often called preformed vitamin A. It can be converted to retinal and retinoic acid, other active forms of the vitamin A family (1-4).

Some plant foods contain darkly colored pigments called provitamin A carotenoids that can be converted to vitamin A. In the U.S., approximately 26% and 34% of vitamin A consumed by men and women is provided by provitamin A carotenoids (1).

Beta-carotene is a provitamin A carotenoid that is more efficiently converted to retinol than other carotenoids (1-4).

For example, alpha-carotene and b-cryptoxanthin are also converted to vitamin A, but only half as efficiently as beta-carotene (1). Lycopene, lutein, and zeaxanthin are other carotenoids commonly found in food. They are not sources of vitamin A but may have other health promoting properties. The Institute of Medicine (IOM) encourages consumption of carotenoid-rich fruits and vegetables for their health-promoting benefits.

Vitamin A plays an important role in vision, bone growth, reproduction, cell division and cell differentiation, which is the process by which a cell decides what it is going to become (1, 5-8).

It helps maintain the surface linings of the eyes and the respiratory, urinary, and intestinal tracts (9). When those linings break down, bacteria can enter the body and cause infection (9). Vitamin A also helps maintain the integrity of skin and mucous membranes that function as a barrier to bacteria and viruses (10-12).

Vitamin A helps regulate the immune system (2, 5, 13). The immune system helps prevent or fight off infections by making white blood cells that destroy harmful bacteria and viruses. Vitamin A may help lymphocytes, a type of white blood cell that fights infections, function more effectively.

Some carotenoids, in addition to serving as a source of vitamin A, have been shown to function as antioxidants in laboratory tests. However, this role has not been consistently demonstrated in humans (1). Antioxidants protect cells from free radicals, which are potentially damaging by-products of oxygen metabolism that may contribute to the development of some chronic diseases (3, 14-16).

What foods provide vitamin A?

Preformed vitamin A is found in animal foods such as whole eggs, whole milk and liver.

Most fat free milk and dried nonfat milk solids sold in the US are fortified with vitamin A to replace the vitamin A lost when the fat is removed (17). Fortified foods such as fortified breakfast cereals also provide vitamin A. Provitamin A carotenoids are abundant in darkly colored fruits and vegetables. Tables 4 and 5 at the end of this document list animal sources of vitamin A and a variety of plant sources of provitamin A carotenoids (18).

It is important for you to regularly eat foods that provide vitamin A or beta-carotene even though vitamin A is stored in the liver (2). Stored vitamin A will help meet needs when intake of provitamin A carotenoids or preformed vitamin A is low (19, 20).

What is the Recommended Dietary Allowance for vitamin A for children and adults?

The latest recommendations for vitamin A are given in the Dietary Reference Intakes developed by the Institute of Medicine.

Dietary Reference Intakes (DRIs) is the umbrella term for a group of reference values used for planning and assessing diets for healthy people.

One of those references values, the Recommended Dietary Allowance (RDA), is the average daily dietary intake level sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each age and gender group (1).

RDAs for vitamin A are listed as Retinol Activity Equivalents (RAE) to account for the different activities of retinol and provitamin A carotenoids. In the table below, RDAs are also listed in International Units (IU) because food and some supplement labels list vitamin A content in International Units (1 RAE in micrograms (ug) = 3.3 IU). The 2001 RDAs for adults and children (21) in ug RAE and IUs are:

Table 1: Recommended Dietary Allowances for vitamin A in micrograms (ug) Retinol Activitiy Equivalents (RAE) and International Units (IUs) for children and adults

Table 2: Adequate Intake for vitamin A in micrograms (ug) and International Units (IU) for infants (21)

There is insufficient information to establish a RDA for vitamin A for infants. An adequate intake (AI) has been established that is based on the amount of vitamin A consumed by healthy infants who are fed breast milk (21).

Results of two national surveys, the third National Health and Nutrition Examination Survey (NHANES III 1988-91) (1, 21) and the Continuing Survey of Food Intakes by Individuals (CSFII 1994) (1, 22) suggested that dietary intakes of some Americans do not meet recommended levels for vitamin A. These surveys highlight the importance of encouraging all Americans to include dietary sources of vitamin A in their daily diets.

There is no RDA for beta-carotene or other provitamin A carotenoids. The Institute of Medicine report suggests that consuming 3 to 6 mg of beta-carotene daily will maintain plasma beta-carotene blood levels in the range associated with a lower risk of chronic diseases (1). A diet that provides five or more servings of fruits and vegetables per day and includes some dark green and leafy vegetables and deep yellow or orange fruits should provide recommended amounts of beta-carotene.

When can vitamin A deficiency occur?

Vitamin A deficiency rarely occurs in the United States, but it is still a major public health problem in the developing world.

At least 3 million children develop xeropthalmia, damage to the cornea of the eye, and 250,000 to 500,000 go blind each year from a deficiency of vitamin A (1). Most of these children live in developing countries. Night blindness is one of the first signs of vitamin A deficiency. In ancient Egypt it was known that night blindness could be cured by eating liver, which was later found to be a rich source of vitamin A (2). Vitamin A deficiency contributes to blindness by making the cornea very dry and promoting damage to the retina and cornea(23).

Vitamin A deficiency diminishes the ability to fight infections.

In countries where immunization programs are not widespread and vitamin A deficiency is common, millions of children die each year from complications of infectious diseases such as measles. (9). When there is not enough vitamin A, cells lining the lung lose their ability to remove disease-causing microorganisms. This may contribute to the pneumonia associated with vitamin A deficiency (2,10,11).

There is increased interest in subclinical forms of vitamin A deficiency, described as low storage levels of vitamin A that do not cause overt deficiency symptoms. This mild degree of vitamin A deficiency may increase children’s risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness (8, 23, 24, 25). Children living in the United States who are considered to be at increased risk for subclinical vitamin A deficiency include:

• toddlers and preschool age children,
• children living at or below the poverty level,
• children with inadequate health care or immunizations,
• children living in areas with known nutritional deficiencies,
• recent immigrants or refugees from developing countries with high incidence of vitamin A deficiency or measles, and
• children with diseases of the pancreas, liver, intestines, or with inadequate fat digestion/absorption (9)

Vitamin A deficiency can occur when vitamin A is lost through chronic diarrhea, and through an overall inadequate intake, as is often seen with protein-calorie malnutrition.

Low plasma retinol concentrations indicate depleted levels of vitamin A. This occurs with vitamin A deficiency but also can result from an inadequate intake of protein, calories and zinc. These nutrients are needed to make Retinol Binding Protein (RBP), which is essential for mobilizing vitamin A from your liver and transporting vitamin A to your general circulation (1).

Iron deficiency can also limit the metabolism of vitamin A, and iron supplements provided to iron deficient individuals may improve vitamin A nutriture as well as iron status (1).

Excess alcohol intake depletes vitamin A stores. Also, diets high in alcohol usually do not provide recommended amounts of vitamin A (1).

It is very important for anyone who consumes excessive amounts of alcohol to include good sources of vitamin A in his or her diet. However, Vitamin A supplementation may not be recommended for individuals who abuse alcohol because alcohol may increase liver toxicity associated with excess intakes of vitamin A (1,26 ). A medical doctor would need to evaluate this situation and determine the need for vitamin A supplementation.

Who may need extra vitamin A to prevent a deficiency?
Vitamin A deficiency rarely occurs in the United States, but the World Health Organization (WHO) and the United Nations International Children’s Emergency Fund (UNICEF) have issued joint statements about vitamin A and children’s health. Both agencies recommend vitamin A administration for all children diagnosed with measles in communities where vitamin A deficiency is a serious problem and where death from measles is greater than 1%. In 1994, the American Academy of Pediatrics recommended vitamin A supplementation for two subgroups of children likely to be at high risk for subclinical vitamin A deficiency. These subgroups were children 6-24 months of age who had been hospitalized with measles and hospitalized children older than 6 months (27).

Fat malabsorption can promote diarrhea and prevent normal absorption of vitamin A.

This is most often seen with cystic fibrosis, sprue, pancreatic disorders, and after stomach surgery. Healthy adults usually have a reserve of vitamin A stored in their livers and should not be at risk of deficiency during periods of temporary or short term fat malabsorption. Long-term problems absorbing fat, however, may result in deficiency, and in these instances physicians may advise vitamin A supplementation (9).

Vegetarians who do not consume eggs and dairy foods need greater amounts of provitamin A carotenoids to meet their need for vitamin A (1).

It is important for vegetarians to include a minimum of five servings of fruits and vegetables daily and to regularly choose dark green leafy vegetables and orange and yellow fruits to consume recommended amounts of vitamin A.

What is the association between vitamin A, beta carotene and cancer?

Surveys suggest an association between diets rich in beta-carotene and vitamin A and a lower risk of some types of cancer (2, 28).

There is evidence that a higher intake of green and yellow vegetables or other food sources of beta-carotene and/or vitamin A may decrease the risk of lung cancer (29). However, a number of studies that tested the role of beta-carotene supplements in cancer prevention did not find it to be protective (30). In a study of 29,000 men, incidence of lung cancer was greater in the group of smokers who took a daily supplement of beta-carotene (31).

The Carotene and Retinol Efficacy Trial, a lung cancer chemoprevention trial that provided randomized subjects with supplements of beta-carotene and vitamin A, was stopped after researchers discovered that subjects receiving beta-carotene had a 46% higher risk of dying from lung cancer than those who did not receive beta-carotene (32). The Institute of Medicine (IOM) states that “beta-carotene supplements are not advisable for the general population,” although they also state that this advice “does not pertain to the possible use of supplemental beta-carotene as a provitamin A source for the prevention of vitamin A deficiency in populations with inadequate vitamin A nutriture” (1).

Can an excess intake of vitamin A promote osteoporosis?

Osteoporosis, a disorder characterized by porous, weak bones, is a serious public health problem for more than 10 million Americans, 80% of whom are women.

Another 18 million Americans have decreased bone density, which precedes the development of osteoporosis. Researchers have identified many factors that increase the risk for developing osteoporosis, including being female, thin, inactive, at advanced age, and having a family history of osteoporosis. An inadequate dietary intake of calcium, cigarette smoking and excessive intake of alcohol also increase the risk of developing osteoporosis.

Researchers are now examining a potential new risk factor for osteoporosis: an excess intake of vitamin A.

Animal, human, and laboratory research suggest an association between greater vitamin A intake and weaker bones (33, 34). Researchers have also noticed that worldwide, the highest incidence of osteoporosis occurs in northern Europe, a population with a high intake of vitamin A (35). However, decreased biosynthesis of vitamin D associated with lower levels of sun exposure in this population may also contribute to this finding.

One small study of nine healthy individuals in Sweden found that the amount of vitamin A in one serving of liver may impair the ability of vitamin D to promote calcium absorption (36).

To further test the association between excess dietary intake of vitamin A and increased risk for hip fracture, researchers in Sweden compared bone mineral density and retinol intake in approximately 250 women with a first hip fracture to 875 age-matched controls. They found that a dietary retinol intake greater than 1,500 mcg/day (more than twice the recommended daily intake for women) was associated with reduced bone mineral density and increased risk of hip fracture as compared to women who consumed less than 500 mcg per day (37).

This issue was also examined by researchers with the Nurses Health Study, who looked at the association between vitamin A intake and hip fractures in over 72,000 postmenopausal women.

In this study, women who consumed the most vitamin A in foods and supplements (greater than or equal to 3000 mcg per day as retinol equivalents, which is over three times the recommended intake for adult men and women) had a significantly increased risk of experiencing a hip fracture as compared to those consuming the least amount. (less than 1250 mcg per day of retinol equivalents). The effect was lessened by use of estrogens but still raises questions about the effects of a high intake of vitamin A. In particular this raises questions about the effect of preformed vitamin A or retinol because retinol intake greater than 2000 mcg per day was associated with an increased risk of hip fracture as compared to a retinol intake less than 500 mcg (38).

A recent longitudinal study in more than 2,000 Swedish men was the first to measure blood levels of retinol to assess the risk of fractures in men.

The investigators found that the risk of fractures was greatest in men with the highest serum retinol levels (greater than 75.62 mcg per d/l). The risk of fracture was further increased in men with the highest serum retinol levels. Men with retinol in the 99th percentile (greater than 103.12 mcg per d/l) had an overall risk of fracture that exceeded the risk among men with lower levels of serum retinol by a factor of seven. High vitamin A intake does not necessarily equate to high serum retinol; serum retinol is regulated by factors besides vitamin A intake, including age, gender, hormones and genetics. Serum beta carotene, however, was not associated with the risk of fracture. The researchers’ findings, which are consistent with the results of studies in animals, as well as in vitro (laboratory studies) and epidemiologic dietary studies, suggest that intakes above the Upper Limit or approximately two times that of the RDA, may pose subtle risks to bone health that require further investigation. Vitamin D, which may contribute to osteoporosis, was not measured. Additional clinical studies evaluating vitamin D and calcium as well as retinol for risk of fracture are warranted (39).

On the other hand, the Centers for Disease Control reviewed data from the Third National Health and Nutrition Examination survey (NHANES III), 1988-94, to determine whether there was any association between bone mineral density and fasting blood levels of retinyl esters, a form of vitamin A (40).

Blood levels of retinyl esters in 5,800 participants were in the normal range and researchers did not find any significant associations between bone mineral density and blood levels of retinyl esters. Additional research is needed to clarify the association between high levels of vitamin A intake and osteoporosis.

There is no evidence of an association between beta-carotene intake, especially from fruits and vegetables (many of which are naturally high in beta-carotene), and increased risk of osteoporosis.

Current evidence points to a possible association with vitamin A as retinol only.

If you have specific questions regarding your intake of vitamin A and risk of osteoporosis, it is recommended that you discuss this information with your physician or other trained health care practitioner to determine what’s best for your personal health.

What is the health risk of too much vitamin A?
Hypervitaminosis A refers to high storage levels of vitamin A in the body that can lead to toxic symptoms. There are three major adverse effects of hypervitaminosis A:

• birth defects,
• liver abnormalities,
• reduced bone mineral density that may result in osteoporosis (1)

Toxic symptoms can also arise after consuming very large amounts of preformed vitamin A over a short period of time.

Signs of acute toxicity include nausea and vomiting, headache, dizziness, blurred vision, and muscular uncoordination (1, 7-9, 41, 42).

Although hypervitaminosis A can occur when very large amounts of liver are regularly consumed, most cases of vitamin A toxicity result from an excess intake of vitamin A in supplements.

The Institute of Medicine has established Daily Tolerable Upper Levels (UL) of intake for vitamin A from supplements that apply to healthy populations (1). The UL was established to help prevent the risk of vitamin A toxicity. The risk of adverse health effects increases at intakes greater than the UL. The UL does not apply to malnourished individuals receiving vitamin A either periodically or through fortification programs as a means of preventing deficiency. It also does not apply to individuals being treated with vitamin A by medical doctors for diseases such as retinitis pigmentosa.

Table 3: Tolerable Upper Intake Levels (UL) for preformed vitamin A in micrograms (ug) and International Units (IU)
for infants, children, and adults (1)

Retinoids are compounds that are chemically similar to vitamin A.

Over the past 15 years, synthetic retinoids have been prescribed for acne, psoriasis, and other skin disorders (43). Isotretinoin (Roaccutane® or Accutane®) is considered an effective anti-acne therapy.

At very high doses, however, it can be toxic, which is why this medication is usually saved for the most severe forms of acne (44-46). The most serious consequence of this medication is birth defects. It is extremely important for sexually active females who may become pregnant and who take these medications to use an effective method of birth control. Women of childbearing age who take these medications are advised to undergo monthly pregnancy tests to make sure they are not pregnant.

What is the health risk of too many carotenoids?
Nutrient toxicity traditionally refers to adverse health effects from a high intake of a particular vitamin or mineral. For example, large amounts of active, or preformed, vitamin A (naturally found in animal foods such as liver but also available in dietary supplements) can cause birth defects.

Provitamin A carotenoids such as beta-carotene are generally considered safe because they are not traditionally associated with specific adverse health effects.

The conversion of provitamin A carotenoids to vitamin A decreases when body stores are full, which naturally limits further increases in storage levels. A high intake of provitamin A carotenoids can turn the skin yellow, but this is not considered dangerous to health.

Recent clinical trials that associated beta-carotene supplements with a greater incidence of lung cancer and death in current smokers raised concern about the effects of beta-carotene supplements on long-term health. However, conflicting studies make it difficult to interpret the health risk.

For example, the Physicians’ Health Study compared the effects of taking 50 mg beta-carotene every other day to a placebo (sugar pill) in over 22,000 male physicians and found no adverse health effects (47). Also, a trial that tested the ability of four different nutrient combinations to inhibit the development of esophageal and gastric cancers in 30,000 men and women in China suggested that after 5 years those participants who took a combination of beta-carotene, selenium and vitamin E had a 13% reduction in cancer deaths (48).

One point to consider is that there may be a relationship between alcohol and beta-carotene because “only those men who consumed more than 11 g per day of alcohol (approximately on