Having too much vitamin D can increase the risk of adverse events such as fractures, falls, and the formation of kidney stones, physicians reported on Friday at the American Academy of Dermatology annual meeting in San Diego.
Health concerns associated with having vitamin D insufficiency or deficiency have captured many headlines in popular media and some medical circles, said Martin A. Weinstock, M.D., Ph.D., a specialist in dermatoepidemiology at Brown University.
"However, there's been much less attention devoted to possible harms resulting from too much vitamin D. That's an issue because people are taking all sorts of vitamin D supplements, which for the most part is fine, but they can overdo it," he said.
The Institute of Medicine recommends intake levels of 400, 600, and 800 international units (IU) daily for infants, healthy adults, and people over age 70, respectively. Vitamin D can be synthesized in the skin after UV exposure, or it can come from diet (naturally or through vitamin D fortification) or from relatively inexpensive supplements, he said. The Institute of Medicine advises people over age nine years old against taking more than 4,000 IU daily.
"There's lots of hype about how vitamin D can help for all sorts of diseases, but by and large those claims are unproven," Dr. Weinstock said.
Vitamin D's only proven benefit is in promoting musculoskeletal health, but now that has come into question.
Two randomized, controlled trials that investigated doses of 300,000 IU and 500,000 IU vitamin D for up to four years showed no reduction in fractures and falls. In fact, both of these studies showed an increased risk of fractures (49 percent in the 300,000 IU study) versus placebo. The 500,000 IU study also showed a 15 percent higher risk of falls, occurring mostly in the first three months post-dose.
A year-long clinical trial that investigated monthly doses of 60,000 IU in patients over 70 years old showed an increased risk of falls as well. Additionally, the 36,000-patient Women's Health Initiative trial randomized women in their 50s, 60s, and 70s to 400 IU of vitamin D and 1 g of calcium daily or placebo. Investigators observed a 17 percent higher risk of calcium kidney stones in patients who got the vitamin D and calcium supplementation.
"The bottom line: Vitamin D is an essential vitamin. People need to have adequate amounts. If they're low, they can supplement to get up to an appropriate amount,” he said.
Dr. Weinstock has been a consultant for AbbVie and Celgene.
F036 - Controversies in Vitamin D. “Adverse impacts of vitamin D.” Martin A. Weinstock, M.D., Ph.D. 5 p.m., Friday, Feb. 16, 2018. American Academy of Dermatology 2018 annual meeting, San Diego.
Jia-Guo Zhao, MD; Xian-Tie Zeng, MD; Jia Wang, MD; et al. "Association Between Calcium or Vitamin D Supplementation and Fracture Incidence in Community-Dwelling Older Adults a Systematic Review and Meta-analysis," JAMA, Dec. 26, 2017. DOI:10.1001/jama.2017.19344
Smith H, Anderson F, Raphael H, Maslin P, Crozier S, Cooper C. Effect of annual intramuscular vitamin D on fracture risk in elderly men and women – a population-based, randomized, double-blind, placebo-controlled trial. Rheumatology (Oxford). 2007;46(12):1852-7.