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Vitamin D toxicity is extremely rare, says a new study.

Supplementation of the vitamin/hormone has been increasing in the last few years, but there's been little consensus on whether overdosing on vitamin D is possible. Existing evidence for vitamin D toxicity, primarily hypercalcemia, has been based almost exclusively on case reports.

But after looking at 25(OH)D levels in more than 20,000 individuals, researchers found that though levels of vitamin D higher than 50 ng/mL were far more common in 2011 than in 2002, there was not an increase in acute clinical toxicity.

In fact, only one patient presented with clinical toxicity, with levels of 364 ng/mL, according to the study, which was published in the May edition of .

But there may still be downsides to high levels of supplementation, according to lead author Daniel Dudenkov, MD, of the Mayo Clinic, and colleagues.

"Even if 25(OH)D values above 50 ng/mL, or even above 100 ng/mL, are unlikely to cause acute toxicity, achieving 25(OH)D values of 50 ng/mL has not been found to be beneficial, especially for the general population," they wrote. "On the contrary, several studies have found an association between 25(OH)D concentrations above 30 to 60 ng/mL and an increased risk of all-cause mortality, cardiovascular disease, cancers, and falls and fractures."

Data for the current analysis were taken from the Rochester Epidemiology Project in Minnesota, where the participants were overwhelmingly white (90% in 2002, and 86% in 2010) and had limited exposure to the sun during winter months. Vitamin D levels were measured in a laboratory, but researchers weren't able to determine if high levels were due to supplements prescribed by doctors or from participants taking supplements on their own.

Of the individuals in the study, 1,714 (8.4%) had vitamin D levels above 50 ng/mL; 123 (0.6%) and 37 (0.2%) had levels above 80 and 100 ng/mL, respectively.

Levels weren't related to the risk of hypercalcemia. In a review of the medical records, four people were found to have hypercalcemia with levels of 50 ng/mL or higher, but only one case involved clinical toxicity.

, at Boston University, wrote in an that there are widespread concerns from physicians around the world that too much vitamin D can increase the risk for kidney stones and cardiovascular complications.

"The concept that vitamin D is one of the most toxic fat-soluble vitamins has been instilled in the psyche of health regulators and the medical community," he wrote.

But such concerns are unfounded, he argued.

"The evidence is clear that vitamin D toxicity is one of the rarest medical conditions and is typically due to intentional or inadvertent intake of extremely high doses of vitamin D (usually in the range of >50,000-100,000 IU/d for months to years)," Holick wrote.

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