Vitamin D has been reported to have a wide range of benefits. However, a recent case study indicates that excessive use of vitamin D can cause kidney damage in people who are not deficient in the vitamin.
The article was published online April 8 in the Canadian Medical Association Journal.
"The aim of this case study is to inform a wider audience that vitamin D at large doses [10,000 IU daily] in patients with normal serum vitamin D levels can lead to toxicity," first author Bourne Auguste, MD, University of Toronto, Ontario, Canada, told Medscape Medical News.
"The public should know that taking more vitamin D than is recommended does not necessarily lead to added benefit. Rather, it can lead to increased harm and specifically kidney failure," he added.
Because vitamin D has a wide therapeutic range, toxicity is rare, Auguste and colleagues note. However, as a fat-soluble vitamin, high doses of it taken for extended periods can lead to buildup.
"Many patients think of vitamin D as a simple supplement with no harm and perhaps historically overstated benefits," Auguste said. "Given that it is so readily available in various over-the-counter formulations and the perception that it has many benefits with no harm, other patients [besides the one in this case study] may be at risk for vitamin D toxicity and potentially kidney failure."
Vitamin D toxicity has a wide range of symptoms, which can delay diagnosis. Those symptoms include, among others, fatigue, high blood pressure, frequent urination, confusion, and itchiness. Early recognition of vitamin D toxicity may prevent chronic kidney damage.
"Vitamin D toxicity may go unrecognized for a long period of time, given the nonspecific symptoms patients may have on presentation. Patients may be taking over-the-counter supplements without full disclosure," Auguste explained.
Management includes careful review of prescription and over-the-counter medications, limiting exposure to sunlight, decreasing dietary and supplemental sources of vitamin D, and monitoring vitamin D levels in asymptomatic patients. Because it is fat soluble, it can take several months for levels to return to normal. In addition, after stopping vitamin D supplements, calcium levels may continue to increase before reversing.
"Clinicians should also consider adjunctive therapies beyond cessation of vitamin D and calcium supplements, such as hydroxychloroquine, glucocorticoids, and ketoconazole in those patients who are symptomatic to decrease the active form of vitamin D in the body," Auguste advised.
The reported case concerns a 54-year-old man who had recently returned from a trip to Southeast Asia, where he had spent an extended time sunbathing (6–8 hours per day for 2 weeks). Upon returning to Canada, a family physician found that his creatinine level was elevated (132 μmol/L from a baseline of 100 μmol/L). Four weeks later, despite discontinuing antihypertensive medication and diuretics, which could have caused dehydration and elevations in creatinine, the patient's creatinine level was even higher (376 μmol/L), and he was referred to a kidney specialist.