According to Barbara Lewin, a sports nutritionist who works with Olympians and endurance athletes, vitamin D, along with other nutrients, can reduce your risk of stress fractures by optimizing bone density, fighting inflammation, improving muscle strength, and even reducing allergy symptoms.
But as the saying goes, you really can have too much of a good thing: According to recent research published in the Journal of the American Medical Association in 2019, consuming more than the recommended amount of vitamin D – 600 IU (international units) per day – could actually decrease your bone density.
In the study, 311 people (aged 55 to 70) consumed either 400, 4 000, or 10 000 IU of vitamin D in supplement form once a day over a three-year period. They also had their wrist and ankle bone strength and bone density measured at six, 12, 24, and 36 months, and their vitamin D and calcium levels measured at three, six, 12, 18, 24, 30, and 36 months.
Over three years, bone mineral density (BMD) decreased by 1.4 per cent in the group that consumed 400 IU per day, 2.6 per cent in the group that consumed 4 000 IU per day, and 3.6 per cent in the group that consumed 10 000 IU per day. (It’s worth noting that every group saw a slight decrease in bone mineral density; because as we get older, our bones naturally start to decline in density.)
This means that getting more than the recommended amount of vitamin D per day doesn’t do anything to strengthen your bones. Instead, it may lead to weaker bones. According to Steven Boyd, Ph.D., study co-author and director of the McCaig Institute for Bone and Joint Health at the University of Calgary, the reason for the bone-density loss might have to do with the fact that high doses of vitamin D were associated with an increase in a blood marker of bone breakdown and suppression of parathyroid hormone (PTH).
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