Are High-Dose Vitamin D Supplements Bad for You?

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Is more better when it comes to vitamin D supplementation for healthy adults? The answer appears to be no, according to a recent study in JAMA. This study, which involved patients without vitamin D deficiency or osteoporosis, found that high-dose vitamin D supplementation for 3 years was linked to slight decreases in bone density, with the largest decrease found among patients taking 10,000 IU per day group.

vitamin D capsules spill out of a brown bottleVitamin D capsules spill out of a bottle and leave many questioning if taking more is better. Photo Source:

“The takeaway message is that, for healthy adults who are vitamin D sufficient while taking 400 IU daily, there is no further bone benefit to be derived by increasing the vitamin D dose,” co-principal investigators Steven Boyd, PhD, and David Hanley, MD, FRCPC, told SpineUniverse. In this study, 400 IU vitamin D per day for 3 years maintained a vitamin D levels in the blood well above recommended levels, they said.

About the Vitamin D Study

The randomized controlled study included 287 healthy volunteers ages 55 to 70 years, who had normal vitamin D levels at the start of the trial. The participants took either 400, 4000, or 10,000 IU of vitamin D for 3 years. Bone mineral density (BMD) was measured in a forearm bone (radius) and bone in the lower leg (tibia) using an advanced imaging system known as high resolution peripheral quantitative computed tomography (commonly called XtremeCT).

Participants who took 4000 or 10,000 IU/day for 3 years showed significantly greater decreases in total bone mineral density at the radius compared with those who took 400 IU/day (−2.4% and –3.5% versus –1.2%, respectively; P<.001). Total tibial BMD was significantly lower only with the 10,000 IU/day dose compared with the 400 IU/day dose (−1.7% versus –0.4%; P<.001).

Higher doses of vitamin D were also linked to hypercalciuria, which is higher than normal levels of calcium in the urine that can potentially lead to kidney stones or contribute to impaired kidney function, the researchers noted. When calcium intake was reduced, hypercalciuria went away in most patients.

The findings were surprising given that the investigators hypothesized that increased vitamin D supplementation would lead to increased bone strength. They designed the study because some experts have advocated for higher doses of vitamin D supplementation for optimal bone health as well as other benefits including reducing the risk for autoimmune disorders (such as multiple sclerosis) and some cancers.

What About People With Vitamin D Deficiency or Osteoporosis?

“Our study was not designed to determine whether vitamin D was beneficial for people with osteoporosis or who had vitamin D deficiency,” the investigators said. “In fact, it is clear that maintaining adequate vitamin D levels is very important for skeletal health. Rather, our goal was to understand whether otherwise healthy adults (non-osteoporotic [meaning without osteoporosis], adequate vitamin D levels) benefited by taking vitamin D supplementation over and above the recommendations by national health organizations.”

“…It is important to also note that we found no significant effect on bone strength,” the investigators said. “Also, there was no difference between the groups with respect to dual x-ray absorptiometry (DXA) bone density. Therefore, in our study participants with normal bone density, it is unlikely the bone loss we measured would lead to increased fracture risk.”

Concluding Comments from the Vitamin D Study

While the amount of bone loss that occurred over the three-year study in the higher dose groups is not likely to cause a fracture, the findings do show that vitamin D doses of 400 to 2000 IU daily are adequate for bone health in most healthy patients who do not have a vitamin D deficiency or osteoporosis. Doses of 4,000 IU or higher are not recommended for the majority of individuals, the researchers said.

Editorial Comment
This purpose of this article is to report findings from a research study about high-dose vitamin D as published in the Journal of the American Medical Association (JAMA). It is not intended to single out vitamin D and ignore other supplements known to benefit bone health. We encourage you to talk with your doctor or healthcare provider about vitamins and other supplements that may help improve and maintain all aspects of your personal health.

Funding was provided by Pure North S’Energy Foundation.

Dr. Boyd reported other (co-owner of software company that performs finite element analysis; the software was used to analyze the data in this study, but it was provided at no cost and no compensation was received for this work) from Numerics88 Solutions and other (for panel participation honorarium) from Amgen outside the submitted work.

Dr. Hanley reported receipt of grants and personal fees (for speaker honorarium) from Amgen and grants from Eli Lilly outside the submitted work.

Updated on: 09/19/19
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Supplement the Smart Way for Spinal Bone Health
Steven Boyd, PhD
Professor, Department of Radiology
Director, McCaig Institute for Bone and Joint Health
Cumming School of Medicine
University of Calgary
David A. Hanley, MD, FRCPC
Departments of Medicine, Oncology, and Community Health Sciences
University of Calgary
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