Dietary Supplement Causes Widespread Selenium Poisoning

Fran Lowry

September 18, 2010

February 8, 2010 — A dietary supplement containing toxic levels of selenium 200 times greater than the concentration listed on the label caused a widespread outbreak of acute selenium poisoning, affecting 201 people from 10 states, investigators report today in the February 8 issue of the Archives of Internal Medicine.

"Selenium is a naturally occurring mineral required for good health. It is obtained from food, and the recommended dietary allowance is 55 μg/d for persons 14 years or older, with a tolerable upper intake limit of 400 μg/d," write Jennifer K. MacFarquhar, RN, MPH, from the Centers for Disease Control and Prevention, Atlanta, Georgia, and colleagues. "The amount of selenium available in a diverse diet with meat, grains, vegetables, and nuts is typically sufficient to negate the necessity for supplementation."

Symptoms of selenium poisoning include nausea; vomiting; nail discoloration, brittleness, and loss; hair loss; fatigue; irritability; and foul breath odor.

The authors began to investigate an outbreak of acute selenium poisoning after reports of cases of toxicity started to surface in March 2008. They defined a case as the onset of symptoms of selenium toxicity within 2 weeks of ingesting a dietary supplement that was manufactured by a company (designated as "Company A") and purchased after January 1, 2008.

The search for cases was conducted nationally. The investigators administered a questionnaire to 227 affected persons from 9 states, including Florida, Georgia, Kentucky, Michigan, North Carolina, Pennsylvania, Tennessee, Texas, and Virginia. They administered a follow-up questionnaire 90 days after the first interview in Florida, Georgia, Michigan, North Carolina, and Tennessee.

The source of the outbreak was identified as a liquid dietary supplement. It was marketed as being suitable for the "entire family" to provide a balance of nutrients to "maintain energy and sustain health" and was labeled as containing 200 μg of selenium per fluid ounce in the form of sodium selenite, an inorganic form of selenium.

Selenium Concentration Was 200 Times Labeled Concentration

When the US Food and Drug Administration (FDA) tested the supplement, it found the selenium concentration to be 40,800 μg/ounce — approximately 200 times the labeled concentration.

The authors report that 201 cases of selenium poisoning were identified, 1 of which required hospitalization. The median estimated dose of selenium consumed was 41,749 μg/day.

The symptoms most frequently reported were diarrhea (78%), fatigue (75%), hair loss (72%), joint pain (70%), nail discoloration or brittleness (61%), and nausea (58%). Symptoms that persisted for 90 days or longer included fingernail discoloration and loss in 52% of cases, fatigue (35%), and hair loss (29%).

In 8 patients, the mean initial serum selenium concentration was 751 μg/L (reference range, ≤125 μg/L), and the mean initial urine selenium concentration in 7 patients was 166 μg/24 hours (reference range, ≤55 μg/24 hours).

Although 201 cases were identified, the actual number of affected persons was likely greater, the authors note. Because selenium toxicity is so rare, and because the wide array of associated symptoms can be nonspecific, making the diagnosis can be difficult.

When interviewed, patients stated that they had not suspected the supplement had made them ill and never mentioned the fact they were taking it to their physicians. Some increased the dose to try to ameliorate their symptoms. "This highlights the importance of patients informing their health care providers about all dietary supplements, herbal remedies, and over-the-counter medications, in addition to prescription medications," the authors write.

The investigation was limited by potential recall bias among patients and a limited number of clinical specimens available for laboratory testing. There were also substantial barriers to sharing proprietary or personally identifiable information among investigating agencies. Information from individuals calling MedWatch was not shared directly with health departments. Instead, the FDA staff had to ask the callers to contact the health department themselves, the authors comment.

"Had the manufacturers been held to standards used in the pharmaceutical industry, this outbreak may have been prevented," the authors conclude. "Gaps in existing regulations present a significant public health risk, and attention should be directed at correcting them to prevent recurring outbreaks such as this."

Reevaluation of Dietary Supplement Health and Education Act Needed

In an invited commentary, Bimal H. Ashar, MD, MBA, from Johns Hopkins School of Medicine, Baltimore, Maryland, writes that the time has come for lawmakers to reevaluate the Dietary Supplement Health and Education Act, passed in 1994, which allows manufacturers to market their products without submitting proof of efficacy or safety to the FDA.

Dr. Ashar notes that congressional support for the act centered on 4 main points: that it would allow consumers access to safe dietary supplements, that it would improve their health, that it would empower consumers to make choices about their preventive health, and that it would stimulate growth of the supplement industry.

However, patients have no way of distinguishing safe supplements from those that may be harmful, and the FDA is "ill equipped to expeditiously monitor, assess, and take action on potentially unsafe supplements," he writes.

The evidence that dietary supplements treat or prevent disease is lacking, but reports of adverse events continue to surface, Dr. Ashar said. "The fact that most patients do not experience adverse events from their supplement use should not be solely sufficient to justify their promotion without premarket evaluation."

Ms. MacFarquhar and Dr. Ashar have disclosed no relevant financial relationships.

Arch Intern Med. 2010;170:256-261, 262-263.


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.