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Vitamin D supplements are incredibly popular. But are they safe? A new study suggests that they are, finding that even high vitamin D blood levels do not generally result in vitamin D toxicity. Published in Mayo Clinic Proceedings, the study looked at data from 1,714 patients with vitamin D blood levels above 50 ng/ml, which is considered high; normal levels range from 20 to 50 ng/ml. The data came from the Rochester Epidemiology Project, a unique collaboration in Olmsted County, Minnesota (home of the Mayo Clinic) whereby researchers have access to almost all of the medical records for patients in the county. For the new study, vitamin D toxicity was assessed by looking at whether patients had hypercalcemia (a condition in which blood levels of calcium are above normal), which can lead to kidney stones and heart and brain impairment, among other things. Researchers also looked at the patients’ medical records for the patients’ age, sex, race, duration and dosage of vitamin D and calcium supplements, medical diagnoses, medications, and other factors to determine if any hypercalcemia could properly be attributed to vitamin D supplementation. Here’s what they discovered:

• For patients with vitamin D blood levels above 50 ng/ml, vitamin D levels were not significantly associated with blood calcium levels or risk of hypercalcemia.
• Only four cases were identified where vitamin D blood levels were associated with hypercalcemia, but only one of these cases resulted in clinical symptoms of acute toxicity (in a patient with extremely high vitamin D blood levels—364 ng/ml).
• At the same time, people who had blood levels of vitamin D above 50 ng/ml increased substantially between 2002 and 2011—the years the data was collected—and in particular, in women aged 65 years and older.

The findings of the new study are consistent with other research showing that vitamin D toxicity is rare, even in individuals with high vitamin D blood levels. Nevertheless, the researchers caution that few benefits have been demonstrated for levels above 50 ng/ml. In addition, it could be possible that very high vitamin D levels contribute to other health problems besides hypercalcemia, which is the only side effect researchers of the new study looked at. Therefore, it is still advisable that people taking vitamin D supplements follow the guidance of their doctor.

Source: Mayo Clinic Proceedings