Study warns too much vitamin D may actually *decrease* bone density

CALGARY, Alberta — Everybody needs some vitamin D to help absorb calcium and build healthy, strong bones, but are people overdoing it with vitamin D supplements? That’s the question posed by University of Calgary researchers who say too much vitamin D can actually be detrimental to bone health.

Just 10-15 minutes spent in the sun while wearing a bathing suit is enough for our bodies to produce all the vitamin D we will need for the day. However, many people who live in areas with sparse access to sunlight in the winter months, such as Canada, end up taking vitamin D supplements every day to get their daily dose.

While it’s generally not a bad idea to take vitamin D supplements, there are often conflicting guidelines for just how much vitamin D a person should be ingesting on a daily basis. Furthermore, researchers theorized that some Canadians may be taking up to 20 times the amount of vitamin D their body needs because they are dealing with any one of a variety of medical conditions that might be related to a lack of vitamin D.

All of these factors lead the research team to pose the question: How much vitamin D is too much?

“Although vitamin D may be involved in regulating many of the body’s systems, it is the skeleton that is most clearly affected by vitamin D deficiency,” says Dr. David Hanley, one of the principal investigators of the study, in a media release. “Current Health Canada recommendations were set to prevent the bone diseases caused by vitamin D deficiency for the vast majority of healthy Canadians. But it has been more difficult to clearly establish the optimal dose of vitamin D. When we designed this study, there remained a question whether there’s more benefit in taking a higher dose.”

After conducting a three-year study, researchers concluded that there are no health benefits to taking high doses of vitamin D. A total of 300 volunteers between the ages of 55-70 were analyzed, and the research team’s hypothesis was that higher doses of vitamin D would result in stronger and denser bones among participants. The volunteers were split into three groups; one group received 400 IU (international units) of vitamin D per day, the second group received 4,000 IU per day, and the third group received 10,000 IU per day.

For reference, Health Canada recommends Canadian adults under the age of 70 only intake around 600 IU of vitamin D per day, while Osteoporosis Canada recommends that Canadian adults at risk of developing osteoporosis take up to 2,000 IU per day.

Each volunteer had their bone strength and density measured using traditional dual x-rays (DXA), as well as with a new state-of-the-art computed tomography device called an XtremeCT. This new device allowed researchers to examine participants’ bones in greater detail than could have been imagined even a few years ago. Each volunteer was scanned at the beginning of the study, and then again after 6, 12, 24, and 36 months. Vitamin D and calcium levels were also measured via blood and urine samples collected throughout the study.

Researchers took the data collected from the traditional dual x-rays and the XtremeCT device and calculated two different versions of each participant’s bone mineral density (BMD). BMD is the amount of calcium and other minerals found in a particular bone segment.

It’s normal for humans to lose some bone density as we age, and according to the traditional dual x-rays’ findings all three dosage groups displayed a gradual decrease in BMD over the course of the three years. However, the more advanced Xtreme CT device picked up much more pronounced differences in BMD loss among the three dosage groups.

According to the XtremeCT readings, volunteers in the 400 IU group lost 1.4% of their BMD over three years, the 4,000 IU group lost 2.6%, and the 10,000 IU group lost 3.6%. These results were in direct contrast to what researchers expected to find; higher doses of vitamin D seemed to cause a decrease in bone density, not an increase.

“We weren’t surprised that using DXA we found no difference among the treatment arms, whereas with XtremeCT, the latest in bone imaging technology, we were able to find dose-dependent changes over the three years. However, we were surprised to find that instead of bone gain with higher doses, the group with the highest dose lost bone the fastest,” says professor Steve Boyd, one of the study’s principal investigators. “That amount of bone loss with 10,000 IU daily is not enough to risk a fracture over a three-year period, but our findings suggest that for healthy adults, vitamin D doses at levels recommended by Osteoporosis Canada (400-2000 IU daily) are adequate for bone health.”

Researchers also noted that volunteers within the 4,000 and 10,000 IU groups exhibited an elevated risk of developing hypercalciuria, or high levels of calcium in one’s urine. Hypercalciuria is often associated with the development of kidney stones.

“What we can see in this study is that large doses of vitamin D don’t come with a benefit to the skeleton,” concludes co-author Dr. Emma Billington. “For healthy adults, 400 IU daily is a reasonable dose. Doses of 4,000 IU or higher are not recommended for the majority of individuals.”

The study is published in the Journal of the American Medical Association.

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About the Author

John Anderer

Born blue in the face, John has been writing professionally for over a decade and covering the latest scientific research for StudyFinds since 2019. His work has been featured by Business Insider, Eat This Not That!, MSN, Ladders, and Yahoo!

Studies and abstracts can be confusing and awkwardly worded. He prides himself on making such content easy to read, understand, and apply to one’s everyday life.

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