More Vitamin D is not Always Better: U of T Patient Case Study

An unusual case study by clinicians and researchers at the University of Toronto and University Health Network has shown that excessive amounts of vitamin D can lead to kidney failure.

The study describes a 54-year-old man with no prior fractures or documented vitamin D deficiency, whose naturopath had prescribed him a high dose of vitamin D.

The patient, unable to find the specific brand prescribed by the naturopath, substituted another one with a higher concentration of Vitamin D. Over two years, he took up to 12 drops daily, or 12,000 units of vitamin D. He now has kidney failure, due to high blood levels of calcium that led to deposits of calcium in the kidney.

The patient’s kidney function is 34 per cent, compared to normal function at more than 60 per cent.  

“Patients should recognize that vitamin D is a medication, and can be associated with risks, particularly when taken at large doses,” says Dr. Bourne Auguste, a master’s student at U of T’s Institute of Health Policy, Management and Evaluation in the Dalla Lana School of Public Health and a clinical fellow in the home dialysis program at the Toronto General Hospital (TGH), University Health Network. “More is not better in this example.” 

The researchers detail the case in today’s edition of the Canadian Medical Association Journal (CMAJ). Auguste was lead author on the paper, working with two clinician researchers based at TGH and U of T: Joanne Bargman, a professor of medicine, and Carmen Avila-Casado, a professor of laboratory medicine and pathobiology. 

According to Osteoporosis Canada, doses up to 2,000 units daily are safe. They recommend vitamin D doses from 800 to 2,000 units daily for older adults and those at high risk for osteoporosis. 

Vitamin D toxicity is rare, but symptoms can include high blood pressure, confusion and kidney stones. Auguste also points out that not everyone needs vitamin D supplements, and that low-risk patients should speak to their physicians about why they are considering taking it.  

With files from CMAJ and TGH.