In a rare case, a 54-year-old man, after returning from a trip to Southeast Asia where he spent much of his holiday sunbathing, was diagnosed with kidney damage after he took high doses of vitamin D for years.

After referral to a kidney specialist and further testing, it was discovered that the man had been prescribed high doses of vitamin D by a naturopath, who recommended a dose of 8 drops every day, according to a study published in the Canadian Medical Association Journal. Over two-and-a-half-years, the patient, who did not have a history of bone loss or vitamin D deficiency, took 8-12 drops of vitamin D daily, totalling 8,000-12,000 IU.

As a result, he had very high levels of calcium in the blood which left him with significant kidney damage. The recommended daily allowance of vitamin D is 400-1000 IU, with 800-2000 IU recommended for adults at high-risk of osteoporosis and for older adults. "Although vitamin D toxicity is rare owing to a large therapeutic range, its widespread availability in various over-the-counter formulations may pose a substantial risk to uninformed patients," said Bourne Auguste from the University of Toronto.

Clinicians must be aware of the risks of vitamin D use to limit complications related to hypercalcemia. Calcium levels may get worse before getting better in patients even after cessation of supplements, as vitamin D is fat soluble. "Our experience informs us that patients and clinicians should be better informed about the risks regarding the unfettered use of vitamin D," suggested the researchers.