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How Well Does Vitamin D Help Fight Osteoporosis?

Instead of helping fight osteoporosis, high dose vitamin D supplements resulted in lower bone mineral density in leg and arm bones.

Vitamin D has a reputation for building strong bones, so you might expect that taking supplements would help fight osteoporosis. Unfortunately, a study published in JAMA suggests that might be unrealistic (JAMA, Aug. 27, 2019).

Will High-Dose Vitamin D Fight Osteoporosis?

Canadian scientists conducted a randomized controlled trial that lasted three years and included 311 people between 55 and 70 years old. During the study, people took daily vitamin D3 supplements at three different doses. Some took the former RDA of 400 IU while others got 10 times that, 4,000 IU. Finally, one-third of the volunteers took vitamin D at the upper limit considered tolerable of 10,000 IU.

None of the participants had osteoporosis when the trial began. The researchers measured bone mineral density at the beginning and end of the study. Previous studies of vitamin D supplements to fight osteoporosis have been disappointing. As a result, the investigators wondered whether higher doses would be more effective. 

Do Higher Doses Work Better?

The volunteers taking 400 IU vitamin D3 maintained their blood levels of 25-hydroxyvitamin D. Those on higher doses ended the study with higher levels of this measure of vitamin D in the body.

One might expect people taking higher doses of vitamin D3 to develop greater bone mineral density. However, that isn’t what actually happened. Instead, those taking the high dose vitamin D saw a decline in this measurement. Bone mineral density of the leg bone called the tibia dropped among people taking 10,000 IU daily. Those taking 4,000 IU daily saw lower bone mineral density in the radius, an arm bone near the wrist. When the investigators measured bone strength, they found no differences between groups.

Researchers have blamed vitamin D deficiency for falls that result in broken bones. However, this study showed no between-group differences in falls. One person taking high-dose vitamin D developed calcium in the urine, a potential adverse reaction to excess vitamin D in the body.

The investigators concluded:

“These findings do not support a benefit of high-dose vitamin D supplementation for bone health; further research would be needed to determine whether it is harmful.”

We have written previously about the failure of vitamin D supplements to fight osteoporosis effectively. You can learn more from our eGuide to Vitamin D Deficiency.

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About the Author
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies..
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