Description of vitamin D as the “sunshine vitamin” has led many to assume that the secosteroid is not likely to cause any serious harm (despite the fact that solar exposure can cause skin cancer). Yet vitamin D supplementation is increasingly being associated with a host of negative health outcomes including brain lesions, kidney stones, increased bone fractures and increased incidence of allergy and atopy. Despite these reports, many researchers still believe that vitamin D is a wonder drug. The majority of studies referenced to support these assumptions, however, rely largely on surrogate outcomes and speculation. Most also fail to provide a basis in human molecular biology for the apparent benefits observed in their analyses.
Some researchers assume that ancient man obtained high concentrations of vitamin D from the sun on the plains of Africa and conclude that modern humans should do the same. However, anthropologists have no definitive data on the sun exposure of early humans. Other studies discuss instances in which people who live at sunnier latitudes display a lower incidence of some inflammatory diseases. Nonetheless, myriad other variables confound their analyses, and even a quick search of the literature reveals numerous, but less frequently cited, counterexamples. Others have argued for increased vitamin D supplementation on the basis that sunscreens block the production of vitamin D in the skin. However, several studies show that sunscreen does not even seem to significantly block vitamin D production.
In 2009, the US and Canadian governments commissioned the Tufts Evidence-based Practice Center to compile a report on vitamin D for the Institute of Medicine (IOM). In an effort to address the discrepancies observed in the vitamin D literature, this report assessed all studies relating to health outcomes and vitamin D and/or calcium intake. After an evidence-based analysis, the Tufts researchers were able to support a positive association only between vitamin D intake and bone health. In the case of all other chronic or inflammatory conditions analyzed, they found no evidence to support an association between vitamin D intake and improved health. The IOM committee therefore decided not to increase the Daily Recommended Intake of vitamin D and further noted that intake of the secosteroid is associated with adverse health outcomes.
Given that the IOM report was released, the results of randomized controlled trials evaluating the use of vitamin D in a variety of inflammatory conditions continue to demonstrate little benefit, and even harm, from vitamin D supplementation. Well-designed studies recently determined that supplemental vitamin D does not significantly improve cardiovascular disease risk factors, isolated systolic hypertension, tuberculosis and upper respiratory infections. Several studies have called into question the one positive association between vitamin D intake and bone health that the IOM committee was able to support in 2010. In 2013, McAlindon et al. published the results of a randomized placebo-controlled trial showing that vitamin D3 supplementation for a period of two years did not reduce knee pain or loss of cartilage volume in patients with symptomatic knee osteoarthritis. Another such study found increased risk of fracture among elderly women taking vitamin D. A second systematic review found that vitamin D supplementation failed to improve bone health in women with breast cancer.