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Vitamin D is essential for a myriad of bodily functions, including strengthening bones and muscles and facilitating proper nerve function. Most people don’t get enough vitamin D from sunlight and need to take supplements, but you can actually get too much of a good thing when it comes to D.
In a recent Canadian study, researchers measured bone density in participants who took 400, 4,000 or 10,000 IUs of vitamin D daily. Over the course of three years, bone mineral density actually decreased the most in the group taking the highest dosage, coming in at a 3.6 percent loss overall, as compared with the 400 IU group, which saw a decrease of 1.4 percent.
“Our results raise the possibility of harm with higher doses of vitamin D,” says David Hanley, M.D., endocrinologist at the University of Calgary and a lead researcher in the study. “In healthy adults who are not deficient, doses at or above 4,000 IU daily don’t provide any further benefit for bone health.”
Stay the course by taking the recommended 600 IUs daily, and choose supplements containing vitamin D3 (cholecalciferol) rather than D2 (ergocalciferol). D3 is what the body naturally makes in response to sunlight exposure, Hanley says.