Pharmacists Shouldn't Bother Recommending Soy Supplements for Asthma

While some patients may take soy supplements to manage their asthma, a new study suggests there is no solid evidence of improved lung function or clinical outcomes from the supplementation.

First author Lewis Smith, MD, professor of medicine at Northwestern University Feinberg School of Medicine, told Pharmacy Times how pharmacists can apply these findings when counseling asthma patients.

“Pharmacists can say that there is no evidence that taking soy isoflavone supplements will benefit patients with asthma, but there is also no evidence that they will cause any harm,” he said. “If individuals with asthma want to use these supplements for other reasons, there is no reason why they should not.”

The double-blind, placebo-controlled study published in JAMA examined adults and children aged 12 years or older from 19 pulmonary and allergy centers in the American Lung Association Asthma Clinical Research Centers network. All of the participants had poorly controlled asthma and were using controller medications.

The 386 participants were equally divided into 2 groups—half of them received a soy supplement with 100 mg of isoflavones, while the other half received placebo. The patients took 2 divided daily doses for 24 weeks, and at the end of trial period, 345 (89%) of them completed spirometry testing.

Both adherence and diet were analyzed to determine whether these factors could have an effect on the study. The patients reported taking at least 1 dose of the treatment on more than 90% of the follow-up days, and the researchers found no significant changes in diet or intake of vitamins A, C, D, and E in both study groups.

The investigators also saw no significant difference between measures of forced expiratory volume in 1 second (FEV1) when comparing those taking soy supplements to the placebo group. They also did not see significant improvements in the supplement patients’ symptom scores, number of episodes of poor asthma control, and changes in exhaled nitric oxide.

“These findings suggest that this supplement should not be used for patients with poorly controlled asthma,” the researchers concluded.

The researchers did see an increase in levels of plasma genistein, an isoflavone that has been shown to reduce inflammation, among those who received the supplement. The effects of genistein on inflammation may only exist in cell cultures, however, as it did not lead to improvements among the patients in this study.

“We found that the supplement, though able to increase blood levels of the key soy isoflavone genistein, did not improve lung function, symptoms, or measures of inflammation in these individuals,” Dr. Smith explained in a press release.