© Whole Foods Magazine January 2013
Vitamin A and Beta-Carotene Are Miracle Workers: 100 Years of Saving Lives
An Interview with Frank Murray
By Richard A. Passwater, Ph.D.
“The teachings of this book can save the lives of millions worldwide,” I stated on the cover of Frank Murray’s new book, Vitamin A and Beta-Carotene Are Miracle Workers.
Since the early 1970s, I have had the greatest admiration for Mr. Murray, his books and his many contributions to the health industry. Murray has been a soldier in the battle to preserve the health industry and make people healthier. He received the National Nutritional Foods Association’s (now the Natural Products Association) President’s Award in 2006. His many books have educated millions. This new book—for which I had the great privilege and honor of writing the foreword—is yet another that should be read by all.
Murray is a member of the New York Academy of Sciences, was editor of Better Nutrition, Today’s Living, Great Life and Let’s Live (England) magazines. He is the author or co-author of 52 great books on health and nutrition.
It is fitting that Murray’s new book calls attention to the importance of vitamin A anew, 100 years after its discovery in 1913. Vitamin A was the second vitamin discovery after the anti-Beriberi vitamin (later named Vitamin B1) in 1910 by Japanese researcher Umetaro Suzuki, Ph.D. (Tokyo Kagaku Kaishi, 1911). Due to a translation problem, Dr. Suzuki’s discovery went unnoticed in the Western world and for decades the discovery of the first vitamin was mistakenly credited to Polish researcher, Casimir Funk, Ph.D., in 1912 for the same discovery. Vitamin A was discovered independently by two groups around 1913. Elmer V. McCollum, Ph.D., and Marguerite Davis, Ph.D., discovered vitamin A in a series of experiments during 1912–1914 at the University of Wisconsin. Usually, it is written that Dr. McCollum was the discover of vitamin A in 1913. However, also in 1913, Yale researchers, Thomas Osborne, Ph.D., and Lafayette Mendel, Ph.D., discovered vitamin A as a nutrient in butter.
Today, vitamin A is not often in the news for adult health despite in importance to many functions in the body ranging from immune health to epithelial cell and mucus membrane health. In the 1980s, there was considerable interest in the anti-cancer activity of both vitamin A and beta-carotene until a flawed study severely dampened interest in that line of research. We’ll discuss vitamin A and cancer later. What is occasionally in today’s news is how vitamin A is saving the lives of millions of children around the world. We will discuss the news about vitamin A in both childhood and adult health herein.
The words of Howard Schiffer, the founder of the Vitamin Angels charity, have stuck in my mind ever since I heard him ask years ago at a fundraiser during Natural Products Expo East in Baltimore something along the lines of “What would it take to bring people to action if a 747 airplane full of children under the age of five crashed every day? Well, the number of children dying every day from vitamin A deficiency would fill many 747s.”
Thanks to programs such as Vitamin Angels, the distribution of vitamin A has helped reduce the estimated number of deaths in children under five from 16 million in 1970 to less than 8 million annually in 2010. **Dr. Passwater: Is this statistic only for deaths related to vitamin A deficiency? YES
According to the World Health Organization, vitamin A deficiency is estimated to affect approximately one-third of children under the age of five worldwide (1). What is especially tragic is that vitamin A deficiency is estimated to claim the lives of 670,000 children under five annually (2). We’ll discuss why vitamin A deficiency is such a killer of young children shortly, but here’s a mental image to consider: 670,000 young children dying a year is more than 1,800 each day—about four or five 747 plane loads daily.
Additionally, approximately 250,000–500,000 children in developing countries become blind each year owing to vitamin A deficiency, with the highest prevalence in Southeast Asia and Africa (3).
Passwater: Children first. Why does vitamin A deficiency lead to the deaths of so many children?
Murray: Children with a vitamin A deficiency have a greater risk of irreversible blindness and dying from infectious diseases than do children who are vitamin A replete, according to Rebecca L. Surles, Ph.D., of the University of Wisconsin at Madison. A marginal vitamin A status is associated with an increased incidence in the severity of infections, poor growth, iron-deficiency anemia and excessive childhood mortality, say researchers at the University of Stellenbosch in South Africa. In fact, vitamin A status brings a 30% reduction in overall childhood mortality. A vitamin A deficiency is still the leading cause of childhood blindness in many developing countries, with over 500,000 going blind every year.
A deficiency in the vitamin causes damage to the naturally protective mucosa membrane barrier of the respiratory tract, and it is thought that bacteria and viruses take advantage of this damage, according to Ranjit Kumet Kumar Chandra, M.D., of Memorial University of Newfoundland in Canada.
In one study, deaths from diarrheal diseases were reduced by 39%, and there was a 70% reduction in deaths from respiratory diseases when a vitamin A intake was adequate in the children.
A vitamin A deficiency is associated with a compromised immune function in children, reported Richard A. Semba, M.D. Very low birth weight in neonates, especially those who need mechanical ventilation and supplemental oxygen therapy in the early postnatal period, are susceptible to bronchopulmonary dysplasia, which affects the bronchial tubes and lungs, according to Jayant P. Shenai, M.D., of Vanderbilt University School of Medicine in Nashville.
It has been shown that very low birth weight neonates with this condition have low blood concentrations of vitamin A and retinol-binding protein and low liver stores of the vitamin. The protein transports retinol/vitamin A through the blood.
Passwater: You mentioned measles, which is still killing about 500 young children each day—a full 747-load of children. It is making a dreaded comeback in the United States. How does vitamin A protect against measles and its complications?
Murray: While measles transmissions were declared eliminated in the United States in 2000, serious outbreaks occur here and abroad, especially in children who have not been vaccinated. Measles is one of the first diseases to reappear when vaccination rates fall.
These cases occur in children whose parents claim exemption from vaccination because of religious or personal reasons, or the infant is too young to be vaccinated. Outbreaks are often traced to immigrants and refugees who transmit the highly infective virus that is spread primarily by airborne droplets and nasal secretions.
Vitamin A supplements, along with measles vaccination, can reduce the chances of complications from the disease, which include ear and chest infections, diarrhea, fever, vomiting and abdominal pain.
In a study among well-nourished children in California, 50% were deficient in vitamin A. In the United States, the number of children with measles who are deficient in the vitamin is thought to exceed 28%. Children with low levels of vitamin A often have lower levels of antibodies against the measles virus.
As Richard D. Semba, M.D., pointed out in Clinical Infectious Disease, a vitamin A deficiency brings widespread changes in immunity, alterations in mucosal surfaces, impaired antibody responses that challenge protein antigens, changes in lymphocyte (white blood cell) subpopulations and altered T- and B-cell function. He added that the vitamin and its metabolites are immune enhancers that potentiate antibody responses in T–cell-dependent antigens, increase lymphocyte proliferation in response to antigens and mitogens, inhibit apoptosis (cell death) and restore mucosal cell surface integrity and function.
According to Alfred Somer, M.D., when children with measles were given 200,000 IU of vitamin A on two subsequent days, mortality was reduced by at least 50%. Younger children generally get half that amount. He said that vitamin A supplements restore normal vitamin A status, which increases resistance to infections by restoring the normally differentiated epithelia, by providing a more effective barrier to infection and by upgrading the immune system.
Passwater: Vitamin A supplementation is not just for children. Vitamin A deficiency is rampant, and this impacts every nation’s healthcare costs. Vitamin A supplements are life saving for adults as well—especially against the scourges of malaria, cancer, HIV/AIDS and other diseases. How does vitamin A deficiency impact U.S. healthcare costs?
Murray: While the HIV/AIDS population in the United States seems to have stabilized, the Centers for Disease Control and Prevention in Atlanta estimates that one-quarter of HIV-infected people are unaware they are infected, and this accounts for more than half of all new infections. Obviously, this will continue to overwhelm our healthcare system.
HIV and AIDS in the United States remains a major public health crisis, with over one million people estimated to be living with HIV, according to John G. Bartlett, M.D., Richard D. Semba, M.D., and colleagues, evaluated vitamin A levels, helper cells, complete blood counts and serologic markers of liver disease in 179 HIV-infected people, and found that over 19% of them had blood levels consistent with a vitamin A deficiency.
In a study of 60 AIDS patients who were not taking vitamin supplements, and who were not pregnant, 22% had low levels of retinol in their blood, reported Dennis L. Karter, M.D. In studying 84 HIV-positive patients, researchers in Brooklyn, NY, found 31% were carotene deficient, and an additional 40% were in the lower quartile of the normal range, indicating that more than 70% of the patients were either carotene deficient or in the low-normal range.
Many experts contend that the immune-compromising vitamin A deficiencies in the United States are widespread among our children, according to Martha Rumore, Pharm.D. This deficiency has been correlated with decreased resistance to pneumonia, tuberculosis, whooping cough and infectious diseases such as measles. Cancer of the breast, colon, prostate, lung, bladder, skin and elsewhere continue to take a heavy toll on our healthcare facilities.
With the aging population in the United States and around the world, increasing numbers of people are being diagnosed with Alzheimer’s disease, which is one of several forms of dementia. These, and other diseases mentioned in my book, will continue to overwhelm our doctors and hospitals. Fortunately, vitamin A and beta-carotene—which is converted into vitamin A—are key players in protecting the health of Americans.
Passwater: Let’s start with cancer. In the 1960s, early research by Umberto Saffiotti, M.D., of the National Cancer Institute in Washington, D.C., startled attendees at the 9th International Cancer Congress by reporting that vitamin A can prevent cancer. How is that possible?
Murray: Ruth Adams and I often reported on his groundbreaking research. Dr. Saffiotti conducted elaborate experiments with hamsters in which he induced lung cancers by blowing into their lungs some of the same chemical particles that are found in urban air pollution and cigarette smoke.
He determined that, like human beings, the animals do not develop lung cancer unless they are exposed to cancer-causing agents or carcinogens.
In further research, Dr. Saffiotti found the changes that occurred in the cells of the animals’ lungs are changes that precede cancer; eventually 100% of the hamsters developed lung cancer, depending on how much of the cancer-producing chemical they were given. Giving them vitamin A prevented these changes in lung cells and, hence, prevented the cancers.
Passwater: Recently, Norman Maitland, Ph.D., of Yorkshire Cancer Research published a study in the journal Nucleic Acids suggesting that vitamin A and its derivatives are useful against cancer. His study indicated that dietary vitamin A could help treat several forms of cancer due to its ability to control the malignant cells. It appears that cancer cells are under the control of a derivative of vitamin A known as retinoic acid. Dr. Maitland’s study was carried out on prostate cancer cells, but he believes the treatment could apply to other cancers as well.
It has been known for years that low vitamin A blood levels are associated with prostate cancer, but nobody knew the mechanisms involved. Dr. Maitland’s study suggests the possible mechanism. In your book, you discuss how vitamin A deficiency is related to prostate cancer.
Murray: According to Abram Hoffer, M.D., Ph.D., several researchers (Willet and MacMahon in 1984; Nettesheim in 1980; and Prasad and Rama in 1985) found that vitamin A, vitamin A’s analogues (retinoids) and carotene inhibit tumor induction and the promotion phase, as well as causing some tumors to regress.
As reported in Cancer Research, 2,400 men (ages 50 and older) were followed for 10 years, and it was found that 84 men developed prostate cancer. The mean serum vitamin A levels were significantly lower in the prostate cancer patients than in the controls. Also, there was an increased risk of the cancer with decreasing blood levels of the vitamin.
In the 12-year Physicians’ Health Study, which involved 22,000 male doctors, half were given beta-carotene supplements every other day, and the other half received placebos. Those with low beta-carotene levels were one-third more likely to develop prostate cancer.
As reported in Cancer Epidemiology, Biomarkers and Prevention, the consumption of foods rich in beta-carotene and lycopene (tomato products) may reduce the risk of prostate cancer. Lycopene is a vitamin A cousin.
Passwater: In your book, you discuss the extensive research indicating that vitamin A, through its role in immunity, lessens HIV/AIDS incidence and mortality.
Murray: A lack of vitamin A is known to increase the risk of many infections, and it has been associated with a greater risk of HIV in many countries, reported the Journal of Acquired Deficiency Syndrome. The susceptibility may be due, in part, to weakened mucosal epithelial linings around tissues, where integrity depends on the vitamin.
People with low blood levels of beta-carotene or vitamin A are more likely to contract the virus than those with higher intakes. Those with low levels of beta-carotene were 21 times more likely to acquire the HIV infection. Research conducted at the Tucson Veteran’s Administration Medical Center and the University of Arizona Health Sciences Center in Tucson found that those with confirmed HIV infection showed improved immune response as a result of increasing their beta-carotene intakes. Following three months of beta-carotene supplementation, increases were found in natural killer cells and lymphocyte activity, in spite of no changes in total lymphocyte numbers. The researchers theorize that beta-carotene might enhance certain aspects of immune function in HIV-infected people, just as the provitamin A has been shown in other studies to stimulate immunocompetence in healthy people.
Concerning the HIV infection, the natural immune response against the virus is completely inadequate, and once a primary infection is established, it fails to eradicate the virus. With few exceptions, HIV disease is relentlessly progressive, and virtually no one has a spontaneous recovery. Unlike other viruses for which we have successful vaccines, HIV quickly integrates itself into the DNA of the host cell. It remains latent in some cells and essentially invisible to the immune system, reported Margaret I. Johnson, Ph.D., and Anthony S. Fauci, M.D.
Since latency is established very early—within days to weeks after infection—the window of opportunity wherein HIV remains vulnerable to eradication through the immune response is very short, the researchers added. Once latency is established, it has not yet been possible to eradicate the virus, even in patients receiving highly active antiretroviral therapy for extended periods.
Between 10% and 40% of HIV-positive women who give birth will infect their children with the virus, reported Richard D. Semba, M.D. Vitamin A deficiency is common among HIV-infected pregnant women, and nutritional intervention may be a practical and inexpensive way of reducing mother-to-infant transmission of the virus.
Passwater: You also mention that the actual number of deaths from malaria may be underreported and invisible to healthcare systems. Why is vitamin A important in preventing malaria and its complications?
Murray: In India, it is estimated that as many as 277,000 people die from malaria each year. These estimates are based on death rates reported by clinics. However, researchers at the University of Toronto in Canada and elsewhere report that these numbers have been vastly underestimated.
Malaria deaths often occur in the countryside and are invisible to the healthcare system. Family members often give “verbal autopsies,” in which they describe how the patient died, and he/she may never have been officially diagnosed with malaria.
Underreporting of malaria deaths from rural areas is also a problem in Indonesia, Pakistan, Afghanistan, Bangladesh and Myanmar (Burma).
A severe fever, headache and vomiting are early symptoms of a malarial attack. It can destroy red blood cells, which blocks blood flow to the kidneys and other organs. If the spleen is enlarged, the brain can be affected, resulting in coma and possible death.
According to the World Health Organization, 250 million pre-school-age children in over 100 countries are deficient in vitamin A. Of these, between 250,000 and 500,000 lose their sight annually, and they are at an increased risk of dying from malaria and measles. This contributes to the deaths of 1.2–3 million children annually.
Vitamin A deficiency affects the immune system, including alterations in organ morphology, cell numbers and responses to various pathogens and antigens. Low levels of the vitamin are associated with the occurrence of chronic bacterial infections and an enlarged spleen.
A study in Malaria Journal reported that vitamin A supplements, which cost about two cents, can reduce infections in children by one-third. In a study in The Lancet, children in New Guinea (where the P. falciparum family of mosquitoes is rampant) were given vitamin A capsules containing 200,000 IU of vitamin A and 10 mg of vitamin E every three months for 13 months. Children between the ages of 12 and 36 months benefited the most, having 35% fewer episodes of malaria, 26% fewer enlarged spleens and 68% lower parasite density.
In another study in the British journal, 21,906 children, six months to five years of age, received either 200,000 IU of retinol equivalent or a placebo every four months. Those under the age of 12 months were given 100,000 IU. The vitamin A-supplemented children had significantly fewer clinic attendances, hospital admissions and deaths than those given look-alike pills. The mortality rate due to acute gastroenteritis was also lower in the vitamin-treated children.
Passwater: We haven’t made much headway in killing all of the mosquitoes?
Murray: I have a bone to pick with some of the well-intentioned people, who have spent millions of dollars trying to rid certain areas of the insects. While these efforts should continue, we should spend more money in saving the malaria patients, especially the children, with vitamin A and other procedures.
I believe it is impossible to kill all of the mosquitoes, simply because there are too many obscure ponds where they can breed. If you kill them in one country, they simply move to an adjoining country and continue their killing fields.
According to Nature magazine, the P. falciparum family has been around for 100,000–l80,000 years. This is the same family that killed King Tut and his family, who lived in the marshes along the Nile in 1323 B.C. As we have learned in New York, New Jersey, Texas and elsewhere, even with our modern technology, there are enough mosquitoes to kill many people with the West Nile virus.
A great deal of money has been spent developing anti-malaria drugs, which is laudatory, but the bugs simply mutate, use the medications as hors d’oeuvres, and wait for the next batch of chemicals. Unfortunately, many people in the developing countries cannot afford the drugs, and in some areas, one-third of the drugs are counterfeit and, therefore, worthless.
Passwater: The roles of vitamin A extend to many other health conditions, ranging from ulcers to Crohn’s disease. How about diabetes?
Murray: It is estimated that roughly 21 million Americans have diabetes, including 6.2 million who don’t know they have it. Another 54 million are pre-diabetic, meaning that their condition can develop into full-blown diabetes. Worldwide, approximately 5.9% of the population is diabetic, which breaks down to about 246 million people. The numbers increase every day.
Diet has been implicated as a principal risk factor for type-2 diabetes, since a high intake of refined carbohydrates—such as white rice—and sugar is associated with an increased risk of diabetes. Blood levels of vitamins A, E and C have been hypothesized to be lower in those with impaired glucose tolerance, according to researchers at the University of Queensland in Australia.
They found that concentrations of all serum carotenoids—alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein/zeaxanthin and lycopene—decreased, except for lycopene, with declining glucose tolerance status. Beta-carotene had the greatest decrease in those with normal glucose tolerance, impaired glucose metabolism and type-2 diabetes, respectively.
A study in the American Journal of Clinical Nutrition found that higher intakes of mixed carotenoids—alpha-carotene, beta-carotene and lycopene—were associated with lower levels of fasting glucose in men, and their blood levels of beta-carotene were associated with a lower risk of insulin resistance, a prediabetic condition.
A study in the American Journal of Epidemiology evaluated the blood levels of carotenoids in 1,665 people ages 40–74, and found that the highest beta-carotene levels were among those with normal glucose tolerance, but levels declined progressively among those with impaired glucose tolerance and diabetes. Those with impaired glucose tolerance had beta-carotene levels 13% below normal, and those with newly diagnosed diabetes had beta-carotene levels 20% below normal.
Several studies have shown that blood levels of vitamin A are decreased in those with type-1, but not type-2 diabetes, according to T.K. Basu of the University of Alberta in Canada.
Other studies have reported that type-2 diabetes is associated with vitamin A deficiency, which is secondary to an impaired transport mechanism of this vitamin from the liver storage area to the target site, such as the retina of the eye.
Obviously, a great deal more research needs to be done in this area.
Passwater: We’ve been talking about vitamin A in general. Please review the various forms of vitamin A for our readers.
Murray: Vitamin A is available in several forms, with each one possessing different degrees of activity. Two forms are retinol and dehydroretinol.
Retinol—formerly called vitamin A—is found as an ester (i.e., retinyl palmitate) in ocean fish oils, other fats, liver, butterfat and egg yolk. It is biologically active as an alcohol, an aldehyde and an acid.
Dehydroretinol, or vitamin A2, differs from retinol in that: 1) it has an extra double bond and 2) it has about 40% the biological activity. It is found only in freshwater fish, and in birds that eat these fish, hence, it is of limited interest in nutrition. The general term vitamin A is used both for retinol and dehydroretinol.
In addition to the actual forms of vitamin A, related compounds, known as carotenes, are found in fruits and vegetables.
Carotene is also called: 1) provitamin A, because it is converted to vitamin A in the body and 2) a precursor of vitamin A, because it precedes vitamin A.
At least 10 of the carotenoids—of over 600 so far isolated—found in plants can be converted with varying degrees into vitamin A. Four of these compounds—alpha-carotene, beta-carotene, gamma-carotene and cryptoxanthine (the main carotenoid in corn)—are of special interest, due to their provitamin A activity. However, beta-carotene has the highest vitamin A activity, and it provides about two-thirds of the vitamin A necessary for human nutrition.
Vitamin A values in animal foods vary according to the vitamin A value of the food the animal that produced them consumed. Liver from older animals and from animals eating green grass are higher in vitamin A than the livers of younger animals eating dry, bleached foods; the butterfat in milk is usually yellower and higher in vitamin A when the cows are grazing on green pastures.
Fish liver oils are richer natural sources of vitamin A. Fish eat smaller fish or crustaceans, which, in turn, have fed on marine plants that contain provitamin A. Foods such as yellow fruits and vegetables supply vitamin A in the form of vitamin A, vitamin A esters and carotenes.
Passwater: What are some of the main functions of vitamin A, and how does it help protect us?
Murray: A deficiency of vitamin A injures the epithelial cells throughout the body, causing them to become dry and flat, and they slough off when the vitamin is lacking. Xerophthalmia, or dry eyes, due to a vitamin A deficiency, was observed in Japan in 1904, and in children in Denmark in 1917.
Vitamin A is necessary for proper vision, and the retina of the eye contains a pigment—visual purple—which is composed of vitamin A and protein. Without visual purple, vision in subdued light is impaired following exposure to bright light, resulting in night blindness. This affects some people driving at night and when entering a darkened theater.
Up to 100,000 children in developing countries develop blindness due to xerophthalmia each year. Many adults are also affected. Vitamin A is also related to cataracts, macular degeneration, retinitis pigmentosa and other eye conditions.
As outlined in my book, vitamin A deficiency is associated with a host of debilitating illnesses, such as cystic fibrosis, heart disease, alterations in immunity, psoriasis, acne vulgaris, eczema, wound healing, Crohn’s disease and many others.
Passwater: What about the safety of vitamin A and beta-carotene?
Murray: Vitamin A—like vitamins D, E and K—is fat-soluble and stored in the liver, where it becomes a reliable reservoir to guard against possible deficiencies. Pregnant women should have their vitamin A intake—from foods and supplements—monitored by their doctor so as not to harm the fetus. This is of little concern to the mother, but, obviously, the liver of a fetus is very small.
Children should also have their vitamin A levels checked. But, doctors are using 100,000 IU and more to save the lives of many children.
In spite of vitamin A’s alleged toxicity, there are few fatalities in the literature. I recall a misguided man in England, who subsisted on nothing but carrot juice for an extended period. He eventually turned a bright orange from the carotene before kicking the bucket.
The potential risk of vitamin A toxicity is based on the ingestion of excessive amounts of preformed vitamin A in the form of retinol or retinol esters, but not from provitamin forms such as beta-carotene or other provitamin carotenoids, according to John N. Hathcock, Ph.D.
Extensive data show that 50 mg of supplemental beta-carotene every other day—equivalent to 25 mg/day—can be taken for more than a decade without harm, Dr. Hathcock said. Skin coloration is harmless and self-correcting with intake reduction.
A research team at the USDA Human Nutrition Research Center on Aging at Tufts University in Boston, headed by Elizabeth J. Johnson, Ph.D., said that long-term supplementation with vitamin A in doses commonly found in multivitamin supplements does not increase the risk of hypervitaminosis A.
The RDA for vitamin A ranges up to 5,000 IU/day, however, a study at the University of New Mexico School of Medicine in Albuquerque found that doses much larger over an extended period apparently have no harmful effects.
Doses as high as 300,000 IU for up to two years appear to be safer than previously thought, according to a research team at the Istituto Nazionale Tumori in Milan, Italy. They added that pharmacological doses of vitamin A for the treatment of lung cancer can be used with reasonable safety for up to two years.
As previously mentioned, pregnant women need to have their vitamin A intake monitored. Consumption of 25,000–50,000 IU—equivalent to 7,500–15,000 mcg RE—of preformed retinol equivalents daily for several months or more by women of child-bearing age can produce adverse effects, such as liver toxicity and possible birth defects.
Pregnant women who are concerned about vitamin A toxicity should take beta-carotene instead, which does not lead to hypervitaminosis A or birth defects, reported Nestor W. Flodin, Ph.D., of the University of South Alabama College of Medicine in Mobile.
Prolonged use of large amounts of vitamin A—exceeding 50,000 IU as retinol—can result in skin rashes, hair loss and other skin problems, but these are reversed when the vitamin is withdrawn.
Passwater: Our readers thank you for taking the time to chat with us once again and bring us up to date on vitamin A and how it is miraculously saving hundreds of thousands of lives. Your new book has even much more fascinating information. Thank you again for giving me the privilege of writing its foreword. May you write many more! WF
1. World Health Organization, Global Prevalence of Vitamin A Deficiency in Populations at Risk 1995–2005, WHO Global Database on Vitamin A Deficiency.
2. R.E. Black, et al., “Maternal and Child Undernutrition: Global and Regional Exposures and Health Consequences,” Lancet 371 (9608), 243–260 (2008).
3. National Institute of Health, Office of Dietary Supplements, “Vitamin A,” www.dietary-supplements.info.nih.gov/factsheets/vitamina.asp, accessed Nov. 27, 2012.
© 2013 Whole Foods Magazine and Richard A. Passwater, Ph.D.
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