Vitamin D supplements — but not sunshine-induced vitamin D — led to unnaturally high vitamin D blood levels in a Utah study claiming that vitamin D blood levels over 100 ng/ml (250 mol/L) increase the risk of atrial fibrillation in the heart.

The study — presented at the American Heart Association’s annual meeting — followed 132,000 Utah medical center patients. But the high vitamin D levels reported in the study were not created by sun-induced vitamin D production in the skin. The reason: The body naturally destroys excess vitamin D made in the skin as a protective mechanism, so vitamin D toxicity does not occur in people who make vitamin D naturally from sun exposure.

The body does not regulate oral intake of vitamin D the same way, which is why it is possible in some cases for people with very high vitamin D absorption rates to overdose in vitamin D taken as a supplement.

Outdoor workers and indoor tanning clients have vitamin D levels around 40-50 ng/ml on average — in the target range of the 40-60 ng/ml that vitamin D researchers now recommend. The American average today is around 23 ng/ml — deficient, according to the vitamin D research community. A generation ago — before sunscreens were used as a daily-use product — that average was around 32 ng/ml, according to government data.

Many studies now suggest that vitamin D levels above 40 ng/ml reduce the risk of heart failure, many forms of cancer, autoimmune diseases and other health-related problems.

To read more about the Utah study, click here.