Inaccurate labeling and composition of dietary supplements led two patients to take massive overdoses of vitamin D—and in neither case was it easy to identify the source of the patient's vitamin D intoxication.

Both patients were taking supplements made in the U.S.

Dr. Lisa G. Newman, senior author of a report published online September 14th in the Journal of Clinical Endocrinology & Metabolism, told Reuters Health by email, "Physicians must consider Vitamin D intoxication in the differential diagnosis of hypercalcemia, and may need to ask patients repeatedly to elicit the proper history as patients often don't think of vitamins as medications or potentially toxic substances."

Dr. Newman of Beth Israel Medical Center in New York and colleagues first describe a 58-year-old man with no significant medical history who had been complaining for several weeks of fatigue, excessive thirst, polyuria, and poor mentation. By the time the authors saw him, he was obtunded, with a serum calcium level of 15.0 mg/dL, a creatinine level of 1.78 mg/dL, and mild anemia.

Initially, he denied using any medications. After repeated questioning he said he'd been taking multiple dietary supplements for two months, which had been prescribed for him by physicians.

Ultraviolet spectrophotometry and high-performance liquid chromatography revealed that one supplement contained 186,400 IU of vitamin D3, instead of the 1600 IU that was the stated dose on the label. On top of that, the instructions mistakenly recommended 10 capsules a day, instead of one.

In other words, the patient took more than 1.8 million IU of vitamin D3 daily for two months, more than a thousand times what the manufacturer had led the patient to believe he was ingesting.

Calcium levels normalized with IV treatment including normal saline, furosemide, and calcitonin.

The second patient, a 40-year-old man presented with nausea, vomiting, and a serum calcium of 13.2 mg/dL. He complained of excessive thirst, polyuria, and muscle aches.

After several inquiries he admitted to taking multiple dietary supplements for one month. One of these purportedly supplied 1000 IU of vitamin D3 but in fact contained 970,000 IU. This patient too ended up with a dose about 1000 times higher than the label indicated.

Calcium levels normalized with IV hydration alone. The patient was discharged on oral hydration, a low-calcium diet, and no vitamin D-containing dietary supplements.

It took approximately a year for 25-hydroxy vitamin D levels to normalize. Once they fell below 400 ng/mL, both patients became normocalcemic and asymptomatic without long-term sequelae.

"Vitamin D deficiency is relatively common, is associated with osteoporosis, and may be linked to an increased risk of common cancers, cardiovascular disease, and diabetes," Dr. Newman said in her email. "Consequently, sales of vitamin D have risen dramatically and therefore it has become even more urgent that good manufacturing practices are followed in the preparation of these products to avoid unnecessary toxicities."

J Clin Endocrinol Metab 2011. Abstract

David Douglas • Reuters Health Information © 2011