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vitamin d

March 8, 2022 - Vitamin D has become all the rage over the last ten years. Many providers now routinely check levels, and in 2018, 37% of adults 60 years and over reported taking a daily vitamin D supplement. While people may feel like they're being healthy taking large doses of vitamins, there is little evidence from clinical trials that vitamin D supplements do anything. Not to mention, experts can't even agree on what a normal vitamin D blood level should be. Most labs now say that levels greater than 30 ng/ml are "optimal," but there is zero evidence to back up this claim, and bone health benefits plateau around 12 - 16 ng/ml.

Proponents of vitamin D claim that it is a panacea that supports all aspects of health. These claims fly in the face of a mounting number of randomized controlled trials that have found no benefit of vitamin D supplements in everything from cancer prevention to asthma. Even osteoporosis trials have failed to find a positive effect; this is surprising given vitamin D's role in calcium absorption.

A large study (N=21,315) published in Lancet Diabetes Endocrinol looked at the effects of monthly vitamin D supplementation on overall mortality. Adults 60 years and older in Australia were randomized to vitamin D3 60,000 IU once monthly or placebo for 5 years. After a median of 5.7 years, there was no significant difference in overall mortality between the two groups (vitamin D - 5.3% | placebo - 5.1%). An exploratory analysis that excluded the first 2 years of follow-up actually found an increased risk of mortality in the vitamin D group (HR 1·24 [95% CI 1·01-1·54]; p=0·05). Vitamin D levels were checked during the study in a subgroup of patients (N=3943), and the average level was 30.8 ng/ml in the placebo group and 46 ng/ml in the vitamin D group. [PubMed abstract]

Large studies that use overall mortality as the primary outcome are the most compelling because mortality is completely objective and immune to bias. The study above should give patients and providers pause when it comes to vitamin D and its purported benefits.

It's not uncommon to see a major news network report on an observational study that has found some positive association between vitamin D and a favorable outcome. These types of studies are susceptible to confounding and should be taken with a grain of salt. It may be that healthier people are outside more, so their skin makes more vitamin D, or that health-conscious people are more likely to take vitamins.

Patients often ask me what type of supplements they should be taking. My answer has always been the same - I read all the studies, and I don't take anything.


Vitamin D review

Calcium homeostasis