Vitamin A

Also known as "retinol", vitamin A was the first vitamin to be identified and understood. It is essential for growth, bone development, night vision, reproduction, protection of the thymus gland, healthy skin, and for the regulation of epithelial cell differentiation. It also strengthens the mucous membranes in the body, which are our first line of defense against air-borne substances, some of which can cause cancer. Last but not least, vitamin A is a very strong antioxidant. Vitamin A is found in many common foods, including carrots, cantaloupes, pumpkins, sweet potatoes, organ meats such as liver and kidney, spinach, mangos, milk, cod liver oil and butter.

Moss describes the results of several studies that confirm vitamin A's anti-cancer properties. As far back as 1926 we get the first indication that vitamin A helps prevent cancer. A Japanese scientist found that lab animals fed a vitamin A-deprived diet had a higher probability of developing cancer. Further studies two years later showed that this finding applied to people as well. In 1963, vitamin A was found to prevent leukoplakia, which is a condition of the mouth that often precedes cancer. Dr. Umberto Saffiotti, while he was dean of vitamin A studies in America, showed that vitamin A protects mice against several forms of cancer. In 1971, Dr. Raymond Shamberger of the Cleveland Clinic found that vitamin A could reduce the probability of developing skin cancer by 76 percent. In 1975, Norwegian researchers showed that lung cancer risk was greater in men that took lower amounts of vitamin A.

In the early 1980s, Richard Peto, a respected Oxford researcher, claimed that vegetables high in vitamin A reduced cancer risk. He claimed that there was a 40percent reduction in cancer risk for people with above-average consumption of vitamin A versus people that are deficient in the vitamin. A study by scientists at NCI of 2,500 men over 50 years old demonstrated that higher blood levels of vitamin A reduce the risk of prostate cancer. Moss also relates several studies that have shown that people with cancer tend to have lower vitamin A levels, again supporting the theory that vitamin A is important in cancer prevention and treatment.

More recently, studies have shown that vitamin A prevents different kinds of cancer. A study in 1986 at the M.D. Anderson Cancer Center at the University of Texas at Houston found that vitamin A can treat leukoplakia and reverse the dysplasia associated with it. In addition, a 1995 study at the School of Public Health of the University of Minnesota found that vitamin A helps prevent stomach cancer. In a 2002 study at the University of California, San Francisco, Dr. Ervin Epstein, Jr. and his colleagues discovered that mice that were predisposed to develop a common form of skin cancer developed 85percent less and smaller tumors when they had been applied a cream containing a vitamin A derivative than mice that had been applied a cream without the derivative. Dr. Epstein believes that the reason for the results is that the vitamin A compound keeps the cancer cells from continuing to proliferate.

Vitamin A is fat-soluble, which means that it is stored in the liver, kidneys and body fat. This can lead to overdosing on vitamin A since excesses are not easily eliminated from the body. Vitamin A can be quite toxic if taken in high doses over long periods of time. Notwithstanding, it is a very important vitamin of which everyone should make sure they get enough. The dose we recommend in Section III is strong enough to be preventive yet low enough that it is not toxic.

Folic acid

Also known as folate, folic acid is a B vitamin that has an important role in DNA synthesis, in the production of red blood cells and in the maintenance of the nervous system. It is found mostly in green, leafy vegetables, but is also available in oranges, chickpeas, beans, lentils, cantaloupes, watermelon and avocados. It has been shown to prevent certain cancers, birth defects in children, certain cancers in children, and possibly Parkinson's disease.

It has long been known that not getting enough fruits and vegetables in the diet increases the risk of developing colon cancer. Although it was thought that it was the fiber in fruits and vegetables that prevented colon cancer, it is now believed that it is also related to the folic acid content of these foods. Researchers at the Institute of Clinical Science at Royal Victoria Hospital in Belfast found that folate supplementation reduces precancerous cell mutations in the colon that usually lead to cancer in high-risk groups. The people in the study had a history of precancerous growths. This abnormal cellular activity decreased dramatically during the folate supplementation, but returned to its previously high levels when the supplementation stopped. This shows that folic acid can actually stop cellular changes that lead to cancer even after they start occurring.

A 2002 study at Brigham and Women's Hospital and Harvard Medical School demonstrated that folic acid reduces colon cancer risk significantly, especially in cases where there is a family history of this cancer. Researchers found that daily consumption of 400 micrograms (versus those that consumed 200 micrograms or less) reduced the risk by 19 percent in cases with no direct family history, but that the risk was reduced by over 50 percent in those with a direct family history ("direct" meaning a first-degree relative). There is no reason to believe that this preventive effect of folic acid would not occur in men as well.

It has also been found that high doses of folic acid prevent stomach cancer in beagles. Although this does not mean that it has the same effect in people, it would not be a surprising result given that substances that help prevent certain digestive tract cancers usually prevent others. Scientists believe that a lack of folic acid permits the activation of substances that stimulate the growth of tumors in the stomach lining. This is something that still has to be studied in human beings.

Studies have shown that supplementation with high doses of folic acid and vitamin B12 can revert precancerous cells in the lungs. Folic acid levels are reduced in the skin as a result of exposure to the sun's rays, and some scientists believe that it is this depletion of folic acid that raises skin cancer risk.

Researchers also found that childhood acute lymphoblastic leukaemia (ALL) risk was dramatically reduced when mothers took folic acid and iron supplements. Of these two substances, folic acid seems to be the one that most reduces the risk. Childhood leukaemia begins with a genetic change while the baby is still in the womb. Folic acid is also known to reduce the risk of neural tube defects during pregnancy. ALL is the most common type of cancer in children, so women who want to reduce their children's cancer risk should get enough folic acid, before and during pregnancy.

Folic acid levels are reduced in women taking hormones such as estrogens and progestins, which are found in birth-control pills and are also used in hormone replacement therapy. It is believed that this lowering of folic acid is the reason for the increase of breast cancer risk for women taking these hormones. Alcohol consumption also lowers folic acid levels, which is probably one of the reasons that alcohol has been linked to breast cancer.

Low folic acid levels also lead to HPV (Human Papilloma Virus) and cervical neoplasms. HPV usually precedes cervical cancer and is the most common sexually-transmitted disease in the world. Some women are born with a folate gene mutation that has been associated with cervical and endometrial neoplasms. Studies have shown that high-dose folic acid supplementation reduces the number of precancerous cells in women with cervical dysplasia (a precancerous condition). HPV is believed to naturally-exist in the female genital mucosa, but that it only becomes active when the immune system is weak or when folic acid levels are low, so maintaining high folic acid levels should be a priority for all women.

For all these reasons, folic acid is the most important supplement for women. All women should take it. The US Department of Health recommends that pregnant women or those that might become pregnant take folic acid supplements, and the US Public Health Service recommends that all women of child-baring age take folic acid supplements. The elderly should also take folic acid as they generally have lower levels of it. It also can't hurt men to take it as it seems to protect the digestive tract and the prostate.

Vitamin D

Vitamin D is actually considered a hormone because the body synthesizes it from precursor substances found in the skin. This fat-soluble vitamin-hormone is essential for bone strength and density because it increases calcium absorption. In this same fashion, it helps prevent osteoporosis. It has also been strongly associated with decreased risks of cancer, heart disease and multiple sclerosis.

Lower cancer death rates (ovarian, colon, breast, lung and prostate) have been associated with exposure to the sun's UV rays (sunlight), and the reason is believed to be the vitamin D that is generated by the body from exposure to sunlight. Laboratory tests have shown that vitamin D is an angiogenesis inhibitor. Angiogenesis is the process of blood vessel formation through which tumors receive their nourishment; hence, vitamin D helps limit tumors' ability to grow. It is also an apoptosis promoter, thus ensuring that cancer cells will die. Vitamin D stimulates the differentiation of cells and therefore inhibits their proliferation (which would limit the multiplication of cancer cells).

An 8-year study undertaken at the University of California, San Diego found that vitamin D reduces colon cancer risk by up to 80 percent. Another important study also found a significant reduction in colon cancer risk. It seems that vitamin D helps the colon eliminate a toxic acid that promotes the disease. Researchers have found the vitamin D compounds also inhibit the growth of breast cancer cells.

Harvard researchers found that men with the highest levels of vitamin D in their blood had a 45 percent lower probability of developing prostate cancer, especially of the aggressive forms of the cancer. A different study found that vitamin D helps control the growth of prostate cancer cells. Yet another important study found that men who have greater direct exposure to sunlight have significantly lower rates of prostate cancer. The results of these studies are supported by the fact that we produce less vitamin D as we get older and that older men are usually the ones that get prostate cancer. The same applies to black males – they are the ones with the greatest risk and they are the ones that produce the least vitamin D because of the melanin in their skin.

Vitamin D in a way is a double-edged sword. Human beings manufacture vitamin D, but we need sunlight exposure in order to do so. However, we cannot recommend that people expose themselves to the sun as much as possible because, as we know, excessive exposure to the sun can cause skin cancer. Notwithstanding, it is estimated that vitamin D can prevent many more cancer deaths than skin cancer causes, so in the greater balance of things it seems that some regular sunlight exposure might provide a greater benefit than the added skin cancer risk it might generate. This theory is supported by the fact that several types of cancer occur more frequently and kill more people in the Northeastern states of the United States versus the Southwestern states (almost twice as many), and there is no explanation for this phenomenon other than the amount of solar radiation received.

However, some people, such as those with very fair skin and many moles, should probably limit their sun exposure because of the potentially added melanoma risk it carries for them. This aside, it seems that most people will generally improve their health and reduce their risk of developing some form of cancer with moderate, regular exposure to UV rays and/or with vitamin D supplementation. For more information on this controversial topic, see Chapter 14.

Studies have shown that vitamin D also protects against autoimmune diseases such as insulin-dependent diabetes mellitus, multiple sclerosis and rheumatoid arthritis. Researchers have also found that it reduces the levels of cholesterol in the blood, which is supported by the fact that people's cholesterol levels drop in the summer, when less sunlight is available for conversion to vitamin D. Conditions that limit vitamin D synthesis have been linked to high blood pressure risk as well.

Although most doctors and nutritionists believe that the safe upper limit for vitamin D is 2,000 IU per day, at least one study has shown that the safe upper limit, which coincides with the maximum amount of vitamin D that the body can generate from sun exposure, is actually five times as much, or 10,000 IU per day. By no means do we recommend going anywhere near that dose, but we do recommend higher amounts than what most dietary supplements contain.

Although regular exposure to sunlight is the way most of us get our vitamin D, there are other sources. The main dietary sources include vitamin D-fortified milk and dairy products (preferably organic), liver, egg yolk, fatty fish, and cod liver oil. Since most people will find it difficult to get enough exposure to the sunlight to generate the vitamin D levels that they should ideally have and some people should not expose themselves to the sun at all, and since there is little vitamin D in the foods that contain it, supplements should be considered by everyone.

Vitamin B12

Vitamin B12 is essential for the manufacture of amino acids and DNA. Its importance in cancer prevention comes from its close link to folic acid. Both seem to work together, and higher folic acid levels require higher intake of vitamin B12. An important study has shown that vitamin B12, taken in conjunction with folic acid, reduces the number of precancerous cells in bronchial passages of smokers. This vitamin is important for preventing osteoporosis and low bone mineral density in both men and women, since a Tufts University study demonstrated a link between lower levels of B12 and low bone mineral density (LOOK FOR REFERENCE). If you are a vegetarian or are taking a temporary break from animal foods, you will probably become deficient in this important vitamin because it is found mostly in animal products.

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