VITAMIN D NUTRIENT REVIEW
This essential vitamin is really an essential hormone.
by Bill Sardi
From time to time news reports surface about a “cancer cluster” among workers in a building. Often the workers have been assigned to dark basement offices or sealed clean-rooms where they must wear spacesuit–like garb. After an indoor environmental examination, investigators often are unable to correlate any factor in the building with the cancer cases. But what if, rather than a cancer-causing agent, the cancer cases are attributable to a missing protective factor?
Given a growing body of evidence linking cancer with vitamin D deficiency, a question surfaces: Are indoor workers getting sufficient sunlight to make enough vitamin D to protect them from cancer?
Vitamin D is formed in the skin of animals and humans by the action of short-wave ultraviolet light, the so-called fast-tanning sun rays. Precursors of vitamin D in the skin are converted into cholecalciferol, a weak form of vitamin D3, which is then transported to the liver and kidneys where enzymes convert it to 1,25-dihydroxycholecalciferol, the more potent form of vitamin D3.
Fat-soluble vitamin D supplements are available in two forms. Vitamin D3 is believed to exhibit the most potent cancer-inhibiting properties and is the preferred form of the vitamin. More than 10 substances belong to a group of steroid compounds that exhibit vitamin D activity. Vitamin D2 (ergocalciferol), derived from plants and yeast, is a form of the vitamin commonly added to milk and some nutritional supplements. The first vitamin D to be discovered was a crude mixture called vitamin D1; it is not available as a supplement.
Although vitamin D isn’t found in quantity in very many foods, it is acquired from foods such as egg yolks, butter, cod liver oil and from cold-water fish such as salmon, herring and mackerel.
Evidence of vitamin D's protective effect against cancer is compelling. For more than 50 years, documentation in the medical literature suggests regular sun exposure is associated with substantial decreases in death rates from certain cancers and a decrease in overall cancer death rates. Recent research suggests this is a causal relationship that acts through the body's vitamin D metabolic pathways. For instance, some evidence points to a prostate, breast and colon cancer belt in the United States, which lies in northern latitudes under more cloud cover than other regions during the year. Rates for these cancers are two to three times higher than in sunnier areas.
Dark-skinned people require more sun exposure to make vitamin D. The thickness of the skin layer called the stratum corneum affects the absorption of UV radiation. Black human skin is thicker than white skin and thus transmits only about 40 percent of the UV rays for vitamin D production. Darkly pigmented individuals who live in sunny equatorial climates experience a higher mortality rate (not incidence) from breast and prostate cancer when they move to geographic areas that are deprived of sunlight exposure in winter months. The rate of increase varies, and researchers hesitate to quote figures because many migrant black populations are likely to also have poor nutrition and deficient health care that confound statistics somewhat.
Although excessive sun exposure may give rise to skin cancer, researchers as early as 1936 were aware that skin cancer patients have reduced rates of other cancers. One researcher estimates moderate sunning would prevent 30,000 annual cancer deaths in the United States.
Vitamin D may also go beyond cancer prevention and provide tumor therapy. Much ado has been made of pharmaceutical angiogenesis inhibitors—agents that help inhibit the growth of new, undesirable blood vessels that tumors require for nutrient supply and growth. Laboratory tests have shown vitamin D to be a potent angiogenesis inhibitor.
Vitamin D also works at another stage of cancer development. Tumor cells are young, immortal cells that never grow up, mature and die off. Because vitamin D derivatives have been shown to promote normal cell growth and maturation, drug companies today are attempting to engineer patentable forms of vitamin D for anti-cancer therapy.
D Is for Strong Bones
Up until now, vitamin D has been better known for its ability to promote bone strength by increasing calcium absorption. Supplemental vitamin D has been shown to reduce hip fracture risk among elderly women when combined with supplemental calcium. In one study of 3,270 healthy women, mean age 84, 1,634 received 1.2 g calcium and 800 international units (IU) vitamin D3, while the other 1,636 received placebo. During the 18-month study, the supplemented group experienced 43 percent fewer hip fractures, 32 percent fewer nonvertebral fractures, and a 2.7 percent increase in bone density of the proximal femur [upper thigh] vs. the 4.6 percent bone density decrease seen in the placebo group.
Other studies bear out vitamin D's importance to bone health, to the point where it's now widely known that vitamin D deficiency is associated with hip fractures, and that supplementation helps. Unfortunately, not everyone is getting enough vitamin D. A recent study showed that 37 percent of adult hospital patients were deficient in vitamin D upon admission. Two-thirds of these patients did not consume enough vitamin D from dietary sources. Surprisingly, 46 percent of those who took daily multivitamins (most of which provide 400 IU) were also in a state of deficiency. Experts now suggest people take 600 IU vitamin D daily, and up to 800 IU a day for elderly patients, because as people age they do not produce vitamin D from sun exposure as easily as they did when younger.
How Much Vitamin D?
The U.S. Recommended Dietary Allowance (RDA) of vitamin D is 200 IU. Yet, studies have shown that 200 IU per day has no effect on bone status. Reinhold Vieth, Ph.D., of the University of Toronto, published a landmark review of vitamin D in the May 1999 American Journal of Clinical Nutrition. Vieth says adults may need, at a minimum, five times the RDA, or 1,000 IU daily, to adequately prevent bone fractures, protect against some cancers and derive other broad-ranging health benefits.
Vieth says the 1989 RDA of 200 IU is antiquated, and the newer 600 IU Daily Reference Intake (DRI) dose for adults older than 70 is still not adequate. Even the 2,000 IU upper tolerable intake, the official safety limit, does not deliver the amounts of vitamin D that may be optimal, Vieth says. On a sunny summer day, total body sun exposure produces approximately 10,000 IU vitamin D. As a result, concerns about toxic overdose with dietary supplements that exceed 800 IU are poorly founded, Vieth says. His review indicates a person would have to consume almost 67 times more vitamin D than the current 600 IU recommended intake for older adults to experience symptoms of overdosage. Vieth believes people need 4,000 to 10,000 IU vitamin D daily and that toxic side effects are not a concern until a 40,000 IU per day dose.
Harvard researchers agree with Vieth. They suggest that older adults, sick adults, and “perhaps all adults” need 800 to 1,000 IU daily. They indicate that daily doses of 2,400 IU—four times the recommended intake—can be consumed safely.
Those who do follow the suggestion to consume more vitamin D may want to watch for toxicity symptoms of headache, nausea, dizziness, vomiting, loss of appetite and dry mouth—though these are not usually seen outside of underlying health conditions such as kidney or parathyroid hormone dysfunction.
Vitamin D is not prevalent in foods. A study conducted at the Bone Research Laboratory at Boston University School of Medicine revealed that fortified milk may not be a reliable source of vitamin D. Only 29 percent of commercial milk samples tested were within 80 to 120 percent of the amount stated on the label. Vitamin D milk fortification procedures vary widely from dairy to dairy. Some dairies place their vitamin D preparations in refrigerated storage, and others do not, which may affect the vitamin D content of the final product.
Since vitamin D is produced naturally within the body, technically it is a hormone. Vitamin D precursors require cholesterol for conversion into the hormone-vitamin. Without adequate sun exposure, vitamin D precursors turn to cholesterol instead of the vitamin.
If You're Not Getting Enough Sun, Consider a Supplement
Sunshine is still the most economical and beneficial way to improve circulating vitamin D levels. Sunning before 10 a.m. and after 3 p.m. avoids the sun's harshest UV radiation. People who are homebound or who live in areas of winter cloud cover and northern latitudes where the sun is so low in the winter sky that the atmosphere absorbs all the UV radiation needed to convert vitamin D should consider naturally compounded vitamin D3 (cholecalciferol) supplements.
Bill Sardi is a health journalist and consumer advocate in Diamond Bar, Calif. His recent publications include The Iron Time Bomb (Purity Pub., 1999) and All About Eyes Naturally (Avery Publishing Group, 2000).
Reprinted with permission of Bill Sardi, www.knowledgeofhealth.com