This is due to the fact that one well known function of vitamin D is to enhance the efficiency of calcium absorption from the intestine. Besides this action, though, vitamin D is key to several other functions in the body, from muscular performance to immune system function, from kidney function to cardiovascular health to fertility.
Vitamin D promotes insulin secretion (preventing diabetes), inhibits adaptive immunity but promotes innate immunity (protecting from autoimmune diseases and infections), inhibits cell proliferation and enhances cell self-death (protecting from cancer), alters cardiac contractility, stimulates sex hormones production. Vitamin D has a n important effect on reproduction in both women and men: it might influence production of sex hormones (estradiol and progesterone) in women and men, and it is positively associated with semen quality.
Notwithstanding its importance, many people (an estimated 1 billion) are vitamin D deficient (D3 level less than 20 29 ng/ml), i.e. they do not even have the minimal amount of it for correct functioning of these body systems. This is recognized as one of the most common medical conditions in children and adults. Doctors are starting to accept vit D’s important role and prescribe it, although mainly to prevent osteoporosis in post-menopause women.
But its need of supplementation does not end here.
It is calculated that approximately 90% of all vitamin D needed has to be formed in the skin under the effect of ultraviolet radiation UV B. This might be one reason for it being so low in so many people: strict sun protection, predicated in the past 30 years or so to supposedly prevent skin cancers, causes vitamin D-deficiency.
Use of sunscreens: not only do synthetic sunscreens effectively block the healing benefits of the sun, by blocking UVB rays, but they also become absorbed into the skin where they create several potential health problems. Moreover, synthetic sunscreens create a false sense of security by disabling the skin's early reaction for overexposure, the sunburn, which creates other health problems. When sunburn, the skin gets damaged by sun rays through creation of free radicals, which are responsible, among other things, for premature ageing and some cancers. That is why it is a good idea to counter these free radicals with antioxidants in the diet.
The synthesis of vitamin D in the skin is a function of skin pigmentation (at darker skin corresponds a lower synthesis) and of the solar angle, which depends on latitude, season, and time of day. Melanin absorbs 99.9% of the UVB photons into heat that is easily dissipated, which effectively avoids radiation damage that contributes to cell damage. The remaining photons are used for the transformation of 7-dehydrocholesterol found in the skin to the previtamin D3.
This 0.1% of photons use is extremely rapid and robust. The obtained forms of pre-vitamin D (D3) is biologically inactive and require activation in the liver and kidneys.
It is believed that, besides the recent lower sun exposure, also protein losses, gastrointestinal malabsorption (so common in our times) and defective skin synthesis might contribute to the elevated number of people with suboptimal level of such vitamin.
Insufficient dietary intake might be another cause: vitamin D is found in eggs and oily fish. Eggs have been (unjustly) receiving a bad name with the appearance of the cholesterol fright(1) of the past 20 years and oily fish do not get highly consumed by the general population, except probably among Inuit. Also, farmed salmon (the most commonly eaten one) has a mean content of vitamin D of approximately 25% of the mean content found in wild caught salmon. Vitamin D content in food is however minimal importance when compared to vitamin D production from the skin-sun reaction.
Association of vitamin D-deficiency has been found with various diseases including cancer (especially breast, ovarian, prostate, colorectal, multiple myeloma and Hodgkins lymphoma, pancreas, leukemia), heart failure, bone diseases, autoimmune diseases (Multiple Sclerosis, autoimmune thyroid diseases, Systemic Sclerosis, Systemic Lupus Erythematosus , Rheumatoid Arthritis, Chron’s disease), chronic kidney disease, infectious diseases, cardiovascular diseases and hypertension, type II diabetes, infertility, muscular diseases (myopathies, risk of falling, fibromyalgia), asthma and neurological disorders (cognitive performance, depression, Alzheimer’s, schizophrenia).
A series of studies have suggested that low vitamin D increases risk of cancer: in a recent study researchers from Northwestern University found that vitamin D deficiency can increase the risk of aggressive prostate cancer in some men by nearly 500 percent. Lung cancer patients have a better prognosis with vit D3 enhancement by high sun exposure.
Vitamin D supplementation can also increase survival of chronic kidney disease patients. In general, and this is what science reveals, higher vitamin D levels are associated with lower overall mortality.
We hope that this article educated on the beneficial effects of moderate sunlight for providing us the vitamin D requirement for good health. For people who are not exposed to sunlight, a supplement is recommended: at present, most experts agree that daily intake of 1000- to 5000 IU vitamin D in adults and 400 IU in children could reduce the incidence of vitamin D-deficiency-related diseases.
So finally, avoid getting sunburn, but do not avoid the sun: train your skin in spring with the morning to midday sun, exposing your body 15-20 minutes at first and then longer times, without sun protection. Use the coloring of the skin as a gauge for safety against overexposure.
(1) For a complete explanation on cholesterol and cardiovascular health and how to avoid the need of statins, order the series of seminars on Cholesterol on www.puravita.co.nz
References
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