Laird Harrison

March 03, 2014

SAN DIEGO — Eating phytoestrogens might significantly reduce the symptoms of asthma and allergies, a new study suggests.

If borne out by further research, the finding could lead to new dietary recommendations, probiotic treatments, or drugs, said lead investigator Jessica Savage, MD, from Harvard Medical School in Cambridge, Massachusetts.

She presented the study results during a news conference here at the American Academy of Allergy, Asthma & Immunology 2014.

"This is only a first step in showing an association, but it's just one more piece of evidence to support a healthy diet," Dr. Savage told Medscape Medical News.

Phytoestrogens are found in plants and act on some of the same receptors as estrogen. Previous research has shown that the compounds have anti-inflammatory and antioxidant effects.

Lignan phytoestrogens such as secoisolariciresinol are found in many foods, particularly flaxseeds. In vitro studies have shown that these chemicals can scavenge hydroxyl radicals and cause fatty acid peroxidation.

Isoflavone phytoestrogens such as daidzein and genistein, found mainly in soybeans, have shown signs of attenuating allergic airway inflammation in animals.

 
These results don't prove that eating more soy or flax will reduce your risk for allergies or asthma.
 

To look at the effects of phytoestrogens on human beings, Dr. Savage and her team used data from more than 7900 people who answered questions on the National Health and Nutrition Examination Survey (NHANES).

In patients with respiratory diseases and other medical conditions, the researchers looked for correlations between urinary levels of phytoestrogens and body measurements, smoking history, and spirometry results.

In a subset of 2218 people, they measured aeroallergen-specific and total serum immunoglobulin (Ig)E, a marker of inflammation. They also measured enterodiol, enterolactone, daidzein, genistein, O-desmethylangolensin (O-DMA), and equol, which are produced when intestinal bacteria metabolize phytoestrogens.

The researchers found that the more enterolactone and O-DMA in the urine, the less likely a subject was to have wheezed in the previous 12 months or to have been diagnosed with asthma.

In fact, for every natural log increase in urinary enterolactone, the odds of asthma decreased by 8% (95% confidence interval [CI], 3% - 13%). For every natural log increase in urinary O-DMA, there was a 7% decrease in the odds of wheeze (95% CI, 4% - 10%).

Patients in the tertile with the most enterolactone in the urine were 19% less likely to have asthma than those in the tertile with the least enterolactone.

Even after the researchers adjusted for the influence of other phytoestrogens, smoking, age, and sensitization to environmental allergens, they still found a correlation between increased phytoestrogens and decreased asthma and wheezing for these 2 compounds.

A correlation was also seen between increased levels of enterodiol and decreased wheezing.

With increased daidzein levels, the odds of atopy decreased. Patients in the tertile with the most daidzein in the urine were 29% less likely to have atopy than those in the lowest tertile (odds ratio [OR], 0.73; 95% CI, 0.57 - 0.96; P = .03 for trend).

Patients in the tertile with the most daidzein also had a decreased risk for total IgE above 100 kU/L (OR, 0.73; 95% CI, 0.57 - 0.94; P = .02 for trend).

As intriguing as these results might be, they don't prove that eating more soy or flax will reduce your risk for allergies or asthma, said Dr. Savage.

"This study suggests that it might be helpful, but what you really need is an interventional study where you expose people to a lot of flax or soy and measure their allergies and asthma," she said.

The researchers are currently teasing out the importance of intestinal organisms that produce the compounds measured in this study. "The precursors come from flax and soy, but if you don't have the microbiome, you won't be able to manufacture these chemicals," Dr. Savage explained.

Other research has shown that people who take antibiotics and eat phytoestrogens don't produce these metabolites, she said. That raises the possibility that probiotic treatments, in which specific organisms are introduced, might affect allergies and asthma.

Although it is too early to draw conclusions from the research, patients will not risk much if they try to reduce their asthma and allergy symptoms by eating more flax seeds and soy beans, said Todd Rambasek, MD, associate professor of allergy and immunology at the Ohio University Heritage College of Osteopathic Medicine in Athens.

"It's like putting a cold compress on your sprained ankle," he told Medscape Medical News. "Even if there is not a lot of evidence, it's probably not going to hurt your ankle."

This study was funded by the AAAAI, Food Allergy Research & Education, the National Institutes of Health, and the Vinik Family. Dr. Savage and Dr. Rambasek have disclosed no relevant financial relationships.

American Academy of Allergy, Asthma & Immunology (AAAAI) 2014: Abstract 566. Presented March 1, 2014.

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