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Vitamin D experts reviewed 290 observational studies and 172 randomized, controlled trials to assess the effect of vitamin D blood levels and supplementation on health and disease in adults. Bone health was excluded from the review because it is well-established that adequate vitamin D is necessary for proper calcium absorption, mineral balance, and healthy bones.
The majority of observational studies linked low vitamin D levels with higher risks of a host of conditions: heart disease, elevated cholesterol, inflammation, diabetes and insulin resistance, overweight and obesity, multiple sclerosis, mood disorders, declining brain (cognitive) and physical function, infectious diseases, and death (all-cause mortality). These findings were not replicated in most of the randomized trials, in which participants supplemented with 2,000 IU or more of vitamin D per day to protect against future illness.
Further, even among people with vitamin D blood levels the National Institutes of Health defines as, “generally considered inadequate for bone and overall health in healthy individuals” (under 50 nmol/L (20 ng/mL), supplementing with 2,000 IU or more of vitamin D per day did not improve markers of health or reduce disease risk.
One group did benefit from vitamin D supplements: the elderly, particularly older women. In this group, supplementing with 800 IU or more of vitamin D daily reduced all-cause risk of death.
The review suggests low vitamin D levels are a consequence of disease rather than a cause. Lead author Dr. Philippe Autier further explained that although serious diseases such as cancer may reduce vitamin D levels, that doesn’t mean raising levels with supplements would prevent disease development.
Other health experts caution that the review is not a reason to stop taking vitamin D. Dr. Nigel Belshaw of Britain's Institute of Food Research pointed out the review, “does not suggest that taking vitamin D supplements cannot be useful in some cases for some purposes. Neither does it rule out a health advantage of increasing vitamin D levels in the blood for those who are deficient.”
Keep the following in mind when fitting vitamin D into your long term health and wellness plan:
(Lancet Diabetes Endocrinol 2013, online ahead of print; available at: http://dx.doi.org/10.1016/S2213-8587(13)70165-7)