The rise and inevitable fall of Vitamin D [View all]

[HuckleB]

https://www.sciencebasedmedicine.org/the-rise-and-inevitable-fall-of-vitamin-d/#more-42613

"It’s been difficult to avoid the buzz about vitamin D over the past few years. While it has a long history of use in the medical treatment of osteoporosis, a large number of observational studies have linked low vitamin D levels to a range of illnesses. The hypothesis that there is widespread deficiency in the population has led to interest in measuring vitamin D blood levels. Demand for testing has jumped as many physicians have incorporated testing into routine care. This is not just due to alternative medicine purveyors that promote vitamin D as a panacea. Much of this demand and interest has been driven by health professionals like physicians and pharmacists who have looked at what is often weak, preliminary and sometimes inconclusive data, and concluded that the benefits of vitamin D outweigh the risks. After all, it’s a vitamin, right? How much harm can vitamin D cause?

There’s no lack of research on vitamin D. Unfortunately, much of that research has been observational, which can find interesting correlations, but can’t demonstrate cause and effect. While there have been some high-quality, large prospective trials using vitamin D as a therapy, there are also a huge number of smaller, poor-quality trials, many of which have produced positive results that haven’t been replicated in larger studies. The net effect has been lots of positive press, but some persistent questions that may not be as widely understood. A new paper from Michael Allan and colleagues set out to summarize the evidence base for vitamin D across multiple uses. It was published in the Journal of General and Internal Medicine, and is entitled “Vitamin D: A Narrative Review Examining the Evidence for Ten Beliefs.” And scanning the list, most of the common claims and beliefs are there: osteoporosis, falls, colds and the flu, cancer, etc. As a narrative review, it is important to note that this type of paper has a high risk of bias. The authors do state that they preferentially sought out systematic reviews and meta-analyses (which, when well conducted, can produce very objective information) but when wrapped in a narrative commentary, the risk of bias increases. This doesn’t mean the findings are incorrect, but that the conclusions emerging from a narrative review (compared to a well-conducted systematic review) will be less robust and quantifiable. While the paper is behind a paywall, I will touch on each of the myths and the evidence they cite, because the paper neatly summarizes the overall evidence base for many of the claims made for vitamin D that I and other contributors have discussed in past posts.

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#10: No role for routine vitamin D testing

There’s a lack of evidence to demonstrate that routine vitamin D testing is necessary. The Choosing Wisely campaign recommended against routine testing as the results of the test are not likely to change the medical advice you’ll receive, which includes basic lifestyle advice (stop smoking, control your weight, be active, and to focus on getting your vitamin D from food and the sun). Despite the recommendations against testing, it has become widespread: In 2011, US Medicare spent $224 million on vitamin D tests for seniors.

Conclusion: More hype than hope

Despite the correlation of low vitamin D levels with an array of medical conditions, the evidence for supplementation remains unconvincing for most uses. Given the modest benefit, low cost, and relative lack of side effects, vitamin D, when used with calcium, retains a role in the prevention of fractures, along with the possibility it may modestly reduce falls and mortality. As for testing, you might need one if you have osteoporosis, or have any medical condition that affects your ability to obtain or use vitamin D. In the broader population, there’s no clear need for testing at all. This area, like a lot of nutritional research, is plagued with lots of low-quality evidence that is more than likely to steer us in the wrong direction. Until better evidence emerges, taking a cautious approach to vitamin D seems sound. Supplementation at modest doses is safe. If you do decide to supplement, remember that more isn’t better, and keep your dose low enough to avoid potential harms."

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The author, a pharmacologist, assesses the state of the science for several claims regarding Vitamin D supplementation.

Good info!