Vitamin D
It was only 40 years ago when scientists reasoned that vitamin D was necessary for bone health with no other aspects of proper physiologic function. It was correctly assumed that a lack of vitamin D led to the bone condition osteomalacia, or “softening” of the bones in adults and presented as rickets (bowing of the legs) in children. Like much of the Recommended Daily Allowances (RDA) of the day, amounts of vitamins were based on prevention of outward disease conditions, rather than on optimal health. The RDA in 1963 for vitamin D was 400 IU for children and half of that for adults–amounts shown to be just enough for prevention of osteomalacia and rickets. Only in the last several years has our understanding of the importance of vitamin D in other areas of health come to light. Vitamin D is made in our bodies after skin is exposed to sunlight. However, the latest medical dogma that sun exposure will cause skin cancer has caused many people to slather on the sunscreen when outdoors prior to receiving any sun exposure. This fact, along with busy work schedules that prevent us from emerging outdoors in the middle of the day, has created a widespread vitamin D deficiency linked to various forms of cancer, high blood pressure, poor blood sugar control and impaired immunity. Furthermore, as we age, we are less equipped to produce sufficient quantities of this vital nutrient. One study found that age-related declines in kidney function may require older people to ingest more Vitamin D3 to maintain the same blood levels as younger people. Important Facts Vitamin D has 2 main supplemental forms: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Ergocalciferol can be obtained from plant sources while cholecalciferol is the form primarily synthesized in the skin by absorbing light energy from UVB rays. Vitamin D3 is considered to be the more bioavailable form of the vitamin and is the preferred form when supplementing. Both vitamin D2 and D3 may be considered pro-hormones and do not have any intrinsic biological activity – they must undergo further metabolism in the liver and kidney before becoming the final active form 1,25 dihydroxycholecalciferol. The true name of vitamin D is calciferol. Under normal circumstances, vitamin D is manufactured in the body and is not required in the diet (given adequate sun exposure at the correct intensity); its mechanism of action and structure closely resemble that of a steroid hormone. Vitamin D is best known for regulating calcium and phosphorus concentrations in the serum. Vitamin D enhances the absorption of these 2 minerals in the small intestine; if dietary intake of calcium falls below adequate levels, calciferol (vitamin D) in conjunction with parathyroid hormone will mobilize calcium stores from the bones into the serum. Lifestyle Induced Vitamin D Deficiency Vitamin D occurs freely in relatively few foods. Based on this fact and the skin-synthesis model, one must assume that this natural process instilled within the body is the preferred way for humans to obtain vitamin D from sun-stimulated conversion in the skin. While the human body is incredibly efficient at creating vitamin D from sun exposure (it is estimated that full-body exposure for a few hours will create 10,000 IU), it also has excellent control in limiting the creation of potentially toxic amounts of the vitamin as prolonged exposure also results in photo-degradation of vitamin D produced in the skin. However, many factors have compounded the irrelevance of sun exposure as a source of vitamin D. Centuries ago, humans moved northward into cold, sun-limited climates, the majority of us spend most if not all of our days inside, and clothing covers 95% of our skin. Even (now fortified) dietary sources are proving inadequate to offset our lack of vitamin D production. One eight-ounce glass of milk contains only 100 IU vitamin D while other dairy products have little or none of this crucial vitamin added. Cereal has 40 – 100 IU in each serving. Salmon, sardines and mackerel contain roughly 200 – 360 IU vitamin D per 90 gram serving. This leaves strict vegetarians and lactose-intolerant people at a disadvantage, while the elderly (inefficient conversion), the obese and dark-skinned people (additional melanin) have additional challenges producing Vitamin D. Colon, Breast and Prostate Health Approximately 5,000 research papers have been written about vitamin D in the last 40 years; only recently have we begun to appreciate vitamin D’s influence on health. Epidemiologic studies are showing that cancer survival rates are lower when diagnosis occurs in months of lower vitamin D levels suggesting a protective role of the vitamin against cancer growth and development. Research into vitamin D is being conducted on approximately 17 different kinds of cancer, the main forms being breast, prostate and colon. Research is revealing that vitamin D may stop the initiation of cancer and that treatment outcomes may be influenced by vitamin D. A recent review article estimates that 50,000 to 70,000 Americans may die prematurely from cancers due to inadequate vitamin D intake. Vitamin D is thought to influence cancer outcomes through several mechanisms: it promotes cell differentiation, regulates programmed cellular death (apoptosis), limits metatastic spread of cancers and growth of tumor blood supplies (angiogenesis). Precancerous growths (adenomatous polyps) are a colon cancer precursor that are also associated with low vitamin D and calcium intake; a recent trial showed that these polyps tend to recur more frequently in people with lower vitamin D and calcium intakes. Another study showed that vitamin D level at the time of colorectal cancer diagnosis had an effect on survival; lower levels were associated with poorer cancer outcomes. Vitamin D intake of 1,000 IU or more each day correlated with a 50% reduced risk of developing colorectal cancer. Researchers also have studied the relationship between breast cancer, vitamin D and calcium intake. Women with more dense tissue revealed on mammography (which is a stronger risk factor for breast cancer) had lower intakes of vitamin D and calcium. Increased amounts of vitamin D and calcium apparently affect breast tissue composition. In this particular study, women with less dense mammography had a daily intake of only 100 IU vitamin D and 750mg (or more) of calcium. In the Nurses’ Health Study, investigators showed that over time, women with higher levels of vitamin D in their blood had a lower risk of breast cancer, and this association was stronger in women 60 years or older. In prostate cancer, vitamin D enhances the differentiation of new cells (poorly differentiated cells are a cancer harbinger) while it slows the ability of the cancer to proliferate, invade and spread. Another study showed that men without prostate cancer enjoyed more time in the sun and thus had a 50% decreased risk of prostate cancer compared to those who spent relatively little time in the sun. This was related to the observation that sun exposure increased synthesis of vitamin D, exerting the observed protective effect. In men with prostate cancer, the prostate-specific antigen (PSA -a prostate cancer marker in the blood) is followed as an indirect way to monitor cancer growth. Men who were supplemented with vitamin D had a 75% lengthened doubling time of their PSA, meaning that cancer growth was greatly slowed. Widespread Role in Health Studies show a link between vitamin D levels and benefits to bone health, multiple sclerosis, heart health in people with hypertension, and overall mortality. Vitamin D deficiency is also correlated with elevated blood pressure, and along with calcium, vitamin D can significantly lower systolic blood pressure. It is thought that these effects are carried out by vitamin D’s ability to influence the blood pressure-related hormone renin. C-reactive protein is an indirect measurement of general inflammation in the body and elevated levels can be associated with conditions such as heart disease. Vitamin D has been shown to have potent CRP-reducing effects. Another way vitamin D can influence health is through its blood-sugar-stabilizing effects. Diabetes occurs more frequently in people with lower vitamin D levels and vitamin D supplementation helps to reduce blood sugar and increase insulin sensitivity. Vitamin D may also have an effect on immune function. It is hypothesized that influenza is in part related to overall lower levels of vitamin D in the colder times of year, and this may predispose more people to the flu and other winter illnesses. Conclusion From this brief review of vitamin D, it is apparent that optimization of vitamin D levels is of paramount importance for a number of health conditions. Since sunscreen can interfere with the body’s ability to make vitamin D, supplementation can ensure that the body achieves its optimal level of wellness. References
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