Too Much Vitamin D Could Be As Bad For You As Too Little

A new study is the first of its kind to show that there’s a very narrow window for healthy vitamin D levels. Find out what they are. (Photo: Getty Images)

We’ve heard a lot about the benefits of vitamin D for issues like bone health and nutrient absorption, and even weight loss, but there might be a hidden risk for those who frequent the supplement aisle for high doses of this superstar nutrient.

New research from the University of Copenhagen has found an association between cardiovascular deaths and both too-low and too-high levels of vitamin D in the blood.

Scientists and doctors have long determined that too-low levels of vitamin D can be harmful to overall health — and often recommend supplements, since vitamin D is generally obtained from sun exposure and isn’t readily available in the food supply. According to study author Peter Schwarz, MD, a professor in the Department of Clinical Medicine at the University of Copenhagen, the relationship between cardiovascular deaths and too-high Vitamin D levels is a new finding that’s worth our attention.

“We found this inverse J-shaped curve of mortality —which was surprising, as we expected that vitamin D should reach much higher levels to cause damage,” he tells Yahoo Health.

For the many who are told in their yearly checkup that their vitamin D levels are low and to take supplements indefinitely, this could be important news.

The study, published in the Journal of Clinical Endocrinology and Metabolism, tracked participants in the COPD-Study, which included data on follow-ups of 250,000 people over a wide range of ages from a period between 2004 to 2011. More than 16,000 of the participants were registered in the Danish Registry of Causes of Death, where researchers were able to determine mortality.

Related: Overweight? You Might Need More Vitamin D

Mortality risk from a cardiovascular event or stroke seemed to jump roughly twofold when vitamin D levels fell below 50 nmol/L and increase by a 1 to 3 ratio when levels rose to over 100 nmol/L. Somewhere between 50 and 100 nmol/L seemed to be the optimum level, with roughly 70 nmol/L being the sweet spot.

To put those numbers into perspective, if you wanted to raise your Vitamin D levels from 40 nmol/L to 50 nmol/L, you’d have to take a 1,000 IU supplement each day for several months to achieve your desired level of D. 

Since this is such a new discovery, Schwarz says he’d like to see other groups worldwide conduct research on various populations to help confirm the optimal upper level of vitamin D in the body. And he cautions against drawing too many conclusions. “This is an association between vitamin D and mortality by cardiovascular disease, stroke and heart attack and not causal explanation.” 

In the meantime, doctors and consumers should be mindful of their supplementation.

If you have low levels of vitamin D, supplementation is not a problem to raise them up — but it’s generally not meant to be taken continually, for a long time period. “Based on our study we should recommend supplementation to a level between 50 and 100 nmol/L, but if the level [in the body] is higher, one must reduce supplementation,” Schwarz says. “Extensive supplementation with different vitamin D products cannot be recommended.”

Related: Clear Link Found Between Vitamin D Deficiency And Alzheimer’s Disease

That said, Schwarz insists it’s a long-term high level of D in the body that’s problematic — not a short-term increase in D, or taking a strong supplement for a short time. 

Talk to your doctor about getting your vitamin D levels checked.

He can recommend the supplement strength and duration that’s right for you. The Institute of Medicine recommends roughly 400 IU per day of D (see the chart for all the stats), and check out the Vitamin D Council for more on supplementation and getting D from natural sources.

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