Too Much Vitamin D Could Be Risky


Vitamin D is crucial for having strong bones and teeth. In addition, it performs other crucial bodily functions, including controlling immunological response and inflammation. The human body produces vitamin D in response to sun exposure. People can also increase their vitamin D intake by eating particular foods or taking supplements.

Health Canada advises a total daily consumption of 600 international units (IU) for people aged up to 70 years old and 800 IU after age 70 for normal, healthy persons. However, some people are probably taking up to 20 times more than the recommended daily dose in preventing or treating a variety of medical conditions that may be related to not having enough vitamin D. Other sources, such as Osteoporosis Canada, suggest adults at risk of developing osteoporosis, a condition characterized by bone loss, should take 400–2,000 IU of vitamin D. How much vitamin D is therefore adequate, and how much is too much?

The study conducted at the McCaig Institute for Bone and Joint Health at the Cumming School of Medicine aimed to answer this question by examining the dose-dependent effects of vitamin D supplementation on a person’s volumetric bone mineral density (BMD) and strength. The study discovered some important findings that we summarized in this article.

A Look Into The Effect of High-Dose Vitamin D Supplementation

The skeleton is the part of the body that is most obviously damaged by vitamin D insufficiency, said the researchers of the JAMA study, even though vitamin D may be involved in regulating many different bodily systems. For the vast majority of Canadians in good health, Health Canada created recommendations to prevent bone problems brought on by vitamin D insufficiency. However, the ideal vitamin D dosage has proven to be more elusive.

Hence, the researchers designed their study with one question: Is there more benefit in taking a higher dose?

They conducted a double-blind, randomized clinical experiment with 300 volunteers between the ages of 55 and 70 to find the answer to this issue and test their hypothesis that increasing vitamin D dosages would lead to a dose-related improvement in bone density and bone strength. Third of the trial subjects received 400 IU, the third received 4,000 IU, and the other third received 10,000 IU of vitamin D daily.

Using a brand-new, high-resolution computed tomography (CT) scan of the bone at the wrist and ankle termed an XtremeCT; volunteers had their bone density and bone strength assessed. The McCaig Institute’s new Centre for Mobility and Joint Health houses the world’s first XtremeCT, which enables researchers to examine bone microarchitecture in unprecedented depth.

A typical DXA (dual X-ray absorptiometry) bone density measurement was also made. After the beginning of the research, as well as at 6, 12, 24, and 36 months, participants underwent scans. Fasting blood samples were taken at the start of the study, at 3, 6, 12, 18, 24, 30, and 36 months, and annual urine samples to measure calcium and vitamin D levels.

By counting the quantity of calcium and other minerals in a specific section of bone, bone mineral density (BMD) can be calculated. The risk of bone fracture increases with decreasing bone density.

The Findings

According to their investigation, the researchers found that taking large amounts of vitamin D has no advantages. The DXA findings revealed a moderate decline in BMD throughout the trial, with no variations found across the three groups. Adults gradually lose BMD as they age. But the high-resolution XtremeCT assessment of BMD, which is more sensitive, revealed substantial variations in bone loss between the three treatment levels.

In the 400 IU group, total BMD fell by 1.4 percent over the three years, by 2.6 in the 4,000 IU group, and by 3.6 in the 10,000 IU group. Contrary to expectations, supplementing with vitamin D at levels higher than those advised by Health Canada or Osteoporosis Canada did not increase bone density or bone strength. Instead, the XtremeCT discovered a dose-related decline in bone density, with the 10,000 IU per day group experiencing the biggest decline. More research is necessary to discover if large doses may actually harm bone health.

Additionally, the group with the highest dose of vitamin D lost bone the quickest, contrary to the researchers’ expectations that larger doses would result in bone gain. 

The results suggest that vitamin D doses at levels recommended by Osteoporosis Canada (400-2000 IU daily) are adequate for bone health for healthy adults. However, the researchers added that the amount of bone loss caused by 10,000 IU daily is not enough to put a person at risk of fracture over three years.

A finding of the study also pointed to a potential safety issue with consuming large doses of vitamin D. Although there were incidents in all three study arms, the researchers discovered that participants assigned to receive higher doses of daily vitamin D supplementation (4000 IU and 10,000 IU) over three years were far more susceptible to developing hypercalciuria (elevated levels of calcium in the urine), compared to those receiving a lower daily dose. Although hypercalciuria is not uncommon in the general population, it is linked to a higher risk of kidney stones and could impede kidney function.

Note: Insert a small graphic representation of hypercalciuria at the side.

Eighty-seven individuals experienced hypercalciuria. Between the 400 IU (17%), 4000 IU (22%), and 10,000 IU (31%) research groups, the incidence varied dramatically. Calcium intake was decreased if participants in the research had hypercalciuria. Repeat testing usually results in hypercalciuria disappearing.

In conclusion, the study’s findings show that high doses of vitamin D do not benefit the skeleton. A reasonable dose for people in good health is 400 IU per day. For the majority of people, doses of 4,000 IU or more are not advised.

Journal Reference

Burt, L. A., Billington, E. O., Rose, M. S., Raymond, D. A., Hanley, D. A., & Boyd, S. K. (2019). Effect of high-dose vitamin D supplementation on volumetric bone density and bone strength. JAMA, 322(8), 736. 

Related Content
© 2023 KellySearch