Vitamin D Today, in the Past and in the Future
How did we ever get to this point, where so many intelligent, educated people ingest vitamin D supplements, hoping to prevent cancer, cardiovascular disease, diabetes and other diseases, despite lacking evidence that vitamin D will provide this benefit?
One factor in the substantial growth of vitamin D supplementation has been news coverage of vitamin D-related stories. The media thrives (or dies) on ratings, which translate into money. Controversy helps boost ratings. The past decade has been full of controversy about vitamin D, so it has been in the news frequently. The brevity of reporting inevitably omits some information and meaningful explanations, and scientific evidence may be blurred when passionate voices promote vitamin D in the news. People like simple, sensational stories and the thought that a D-vitamin could offer serious long-term disease prevention is widely appealing.
Misunderstanding of vitamin D began with its discovery, when this steroid-hormone was called a vitamin. Often considered a nutrient with only beneficial effects, D is the only vitamin that our bodies can manufacture, in a process triggered by something as ubiquitous as daylight. A couple of decades ago, vitamin D was not an everyday over-the-counter product. Sources of vitamin D available to consumers then: cod liver oil, infant vitamin drops and multiple vitamins, stand in stark contrast to today's plethora of vitamin D products and fortified foods. Despite these developments, we consistently encounter warnings about widespread low vitamin D.
It is not unusual for people to misconstrue reports correlating low vitamin D with sick people to be the same thing as low vitamin D causing or contributing to disease, which is like thinking fever causes disease. Many people are surprised to learn that no clinical trials have shown that vitamin supplementation protects people against cancer, other diseases or extends life. The National Cancer Institute does not recommend for or against the use of vitamin D supplements to reduce the risk of colorectal or any other type of cancer. The Jan. 2015 issue of the British Medical Journal included this advice: "Do not recommend vitamin D supplements to prevent chronic disease because clear evidence of benefit does not currently exist and adverse effects cannot be excluded."
Despite early excitement from observational studies, clinical trials have not borne convincing evidence for vitamin D benefits beyond bone health. New randomized trials are underway, and more will be conducted to study any effects of vitamin D supplementation on cancer and other health outcomes. A recent JAMA paper noted that "clinical enthusiasm for supplemental vitamin D has outpaced available evidence." The paper warned that widespread vitamin D supplementation threatens to jeopardize the ability of researchers to conduct valid randomized clinical trials. Future trials will be informative only if the results are not diluted by enrolled participants using vitamin D supplementation.
There remains a lack of a consensus for an optimal laboratory measure of 25-dihydroxyvitamin D, resulting is a wide range of what is considered normal. Last month, Labcorp once again raised their "normal range" for 1,25-dihydroxyvitamin D from 10-75 pg/mL to 19.9-79.3 pg/mL. With the Mayo Clinic website stating 80ng/mL is "the lowest reported level associated with toxicity in patients without primary hyperparathyroidism and with normal renal function", establishing valid target normal ranges for both D-metabolites obviously remains a challenge that can affect patient health.
We will continue in our efforts to educate people who are ill about the reality of vitamin D supplements and the immediate health effects they may experience from using them. It will be a mistake with lasting implications if widespread vitamin D supplementation keeps science from finally establishing whether there actually is any benefit from vitamin D supplementation, even in the general population.
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