A group from the US Centers for Disease Control (CDC) has reported an outbreak of selenium poisoning due to an incorrectly manufactured dietary supplement product.

Selenium is an essential micronutrient, and a balanced diet generally supplies sufficient amounts for good health: the US recommended intake is 55 microgm/day with an upper limit of 400 microgm/day. It is toxic in acute or chronic excess, with symptoms including nausea; vomiting; nail discoloration, brittleness, and loss; hair loss; fatigue; irritability; and bad breath (likened to garlic breath). Acute poisoning is rare but is reported. In this case, a US chiropractor noted an outbreak of symptoms common to several of his patients and worsening when they increased consumption of a supplement purchased from his practice. This was noted to the local public health department, and an investigation was started; in parallel, a national investigation had been started as a result of similar reports elsewhere.

All the affected patients had used the same liquid selenium supplement. This contained a range of vitamins, minerals, amino acids, essential fatty acids, Spirulina, coenzyme Q10, and antioxidants. It was stated to contain 200 microgm of selenium in the recommended dose (30ml). On testing, it was found to contain up to 40,800 microgm/30ml; it also contained chromium at 17 times the amount stated on the label, although this was below the dose likely to cause toxicity.

Of 227 consumers eventually identified as having used the product, 201 (89%) met the case definition for selenium poisoning. One needed hospitalisation, but there were no fatalities. Where data were available, the median daily dose consumed was 41,585 microgm/day, for a median of 29 days. Symptoms most frequently reported were diarrhoea (78%), fatigue (72%), hair loss (70%), joint pain (67%); hair loss ranged from 10% to 100% (median 50%) with 1 patient reporting loss of all body hair. Where follow-up data were available, symptoms persisted for up to 90 days in significant proportions of people.

Investigation indicated that the product was manufactured for the final distributor using raw materials supplied by a third company. The increased selenium in the final product was found to be due to human error at the raw material supplier. The companies involved were not subject to the manufacturing standards used in the pharmaceutical industry, although these standards are being extended to this sector.

The authors conclude that toxic levels of selenium in a dietary supplement resulted in a widespread outbreak of selenium poisoning. This was exacerbated by the behaviour of many consumers, who did not consider that the supplement may have been responsible for their symptoms, and in some cases increased their dose in attempt to treat them. The manufacturing error responsible would probably have been picked up and the outbreak prevented had the manufacturer been subject to the manufacturing standards used in the pharmaceutical industry.