It's still not clear why some people develop shingles and others don't but researchers have discovered that asthma may have something to do with increasing risks of herpes zoster.

For a study published in the Journal of Allergy and Clinical Immunology, researchers from the Mayo Clinic Children's Research Center analyzed medical records from patients possibly with shingles in Minnesota's Olmsted County. They were able to identify 371 cases, which they then compared to 742 control cases.

Out of the 371 cases of shingles, 87 had asthma, whereas the control group had 114 with the breathing disorder. According to the researchers, adults with asthma were 70 percent likelier to develop shingles compared to those without.

Young Juhn, M.D., lead author for the study, said that asthma is one of five most troublesome chronic diseases in the United States. It affects up to 17 percent of the population and its effects on immune dysfunction or infection risk very well extend beyond airways.

Accounting for asthma and other atopic conditions, the researchers also pointed out that asthma and atopic dermatitis have been found to be connected independently to increased risks for shingles. Herpes zoster occurred in 12 percent of participants with atopic dermatitis (45 out of the 371 from the shingles group) while just 8 percent (58 out of 742) of the control subjects developed the disease.

Researchers still don't know which underlying mechanisms are at play here but they suggest that it may have to do with the immune functions in the airways and skin being impaired in patients with either asthma or atopic dermatitis. Because adaptive immunity is suppressed when asthma is present, it may pose a bigger risk that the varicella zoster virus will be reactivated.

"As asthma is an unrecognized risk factor for zoster in adults, consideration should be given to immunizing adults aged 50 years and older with asthma or atopic dermatitis," said Juhn.

Every year, almost 1 million cases of shingles occur, with a third of all adults in the U.S. affected by the time they hit 80 years old. Zoster vaccination has been associated with lower shingles risk.

Other authors for the study include: Euijung Ryu, Ph.D., Brian Lahr, M.S., Peter Wollan, Ph.D., Barbara Yawn, M.D., Chung-Il Wi, M.D., Eun Na Kim, M.D., Duk Won Bang, M.D., Ph.D. and Hyo Jin Kwon, M.D.

Photo: National Institute of Allergy and Infectious Diseases | Flickr