Is it time to stop taking vitamin D?

Is it time to stop taking vitamin D?

On Nutrition

When I was in grad school about a decade ago, there was a flurry of vitamin D research underway to test the theory that low blood levels of vitamin D contributed to, well, just about every chronic disease under the sun. In class, we talked about how some of these lines of investigation likely wouldn’t pan out. As it turns out, almost all those lines failed to pan out.

As potential links between vitamin D and one health condition after another broke, the link between vitamin D and bone health still seemed certain. Now, data from the vitamin D and Omega-3 Trial published July 28 in The New England Journal of Medicine knocks down even that last bit of nutritional “certainty” — participants randomly assigned to take 2,000 IU (international units) of vitamin D3 per day were no less likely to suffer a bone fracture than those taking a placebo pill.

Researchers followed the 25,871 VITAL participants — half were women and 20% were Black — for an average of 5.3 years. That was long enough to observe 769 new fractures in the vitamin D group, and 782 fractures in the placebo group. Yes, more fractures happened in the placebo group, but the difference was not statistically significant — in other words, the difference was small enough that it could simply be due to chance.

But was following participants for five years long enough? Susan Ott, a UW Medicine physician, professor and researcher who has studied vitamin D, osteoporosis and other bone diseases, said most similar studies have only followed participants for about two years. “This is one of the longest studies we have. I would say that after five years you have a good grasp on whether the fracture rate is better or worse,” she said. “I do think it was a well-done study, and one of the main conclusions is that we just don’t need these high doses of vitamin D.”

Bryan Kestenbaum, a nephrologist and epidemiologist at the UW Kidney Research Institute and a professor at the UW School of Medicine whose areas of research include vitamin D, said large randomized controlled trials like VITAL are expensive to run, but they can provide answers to scientific questions. In this case, do vitamin D supplements reduce fracture risk? “This study answered the question definitively,” he said. “They gave people a good dose, and they followed them for a sufficient amount of time.”

So, should you still take vitamin D?

An accompanying editorial recommended that providers stop testing vitamin D levels or recommending taking vitamin D supplements in the general population, and that “people should stop taking vitamin D supplements to prevent major diseases or extend life.”

Kestenbaum agrees, noting that the authors of the editorial are excellent vitamin D researchers. “Every study of this type is showing that there’s no benefit of taking vitamin D,” he said, adding that it this was true regardless of whether participants had already been taking vitamin D supplements before the study started. It also didn’t matter if their blood levels of vitamin D started out on lower or higher. “I think it’s proven.”

VITAL researchers previously found that vitamin D did not reduce the risk of developing cancer, having a heart attack or stroke, dying from cardiovascular disease, suffering a fall or experiencing depression. It also did not affect body fat. The vitamin D and Type 2 Diabetes randomized controlled trial found that after 2.5 years, taking 4,000 IU of vitamin D3 daily was no better than a placebo at preventing diabetes in high-risk adults.

Ott agrees there’s no reason for most people to be tested. However, she does think that in Seattle we may still need some supplemental vitamin D, but only in the 400-1,000 IU range. Our skin makes vitamin D when it’s exposed to sunlight, which those of us in northern climates get less of. “If you happen to have a bunch of 2,000 IU supplements, take them every few days,” she said.

Why was there so much hype in the first place?

“We’ve known for a long time that people who have definite vitamin D deficiency respond to vitamin D,” Kestenbaum said. “There are a lot of great biological reasons for vitamin D to do all of these things that we thought it would do.” However, he said many of the early observations that got researchers excited about vitamin D came from studying the effects on individual cells in a lab, or in animals. “Sometimes it turns out that what you see in the lab is not always how it plays out in humans.”

What about the big epidemiological — or community — studies that observed that people with lower vitamin D levels have worse health outcomes? “It could be that the lower levels are a marker of something metabolic that we don’t understand,” Kestenbaum said. In other words, the low vitamin D levels could be due to something else that’s also causing the worse health outcomes.

He likened the scientific enthusiasm about vitamin D to the excitement about developing a drug to raise levels of “good” HDL cholesterol (because high HDL levels are associated with lower risk of cardiovascular disease). But once these drugs were developed, they turned out to not be beneficial, and one drug caused significantly more heart attacks and deaths than was seen with a placebo.

Ott cautions that some of the big U.S. labs that process vitamin D tests say that “normal” levels are between 30-100 nanograms per deciliter, whereas the rest of the world says normal levels are between 20-50 ng/dL. There’s been a lot of controversy about that, including accusations of financial conflicts of interest. “It’s an expensive test and the labs are making a lot of money,” she said. “When vitamin D is low, everything they say about it is true. It’s just that the level of what’s low isn’t 20, it’s more like 10. If your levels are around 20-30, you’re probably going to be pretty safe.”


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