The researchers say consideration should be given to immunizing adults aged 50 years and older with asthma against shingles.
There are an estimated 1 million cases of shingles every year in the US. Despite its prevalence - particularly among those aged 50-59 - it is unclear why some people develop the illness while others manage to escape it.
Shingles is caused by the varicella zoster virus - the same one that causes chickenpox. Anyone who has recovered from chickenpox may develop shingles - even children.
After a person recovers from chickenpox, the virus stays dormant in the body. While it is possible to have a second or even a third episode, typically people who have shingles only have one episode in their lifetime.
Asthma is a common long-term condition that inflames and narrows the airways, causing wheezing, coughing, chest tightness and breathlessness.
It is one of the five most burdensome chronic diseases in the US, affecting more than 25 million Americans, including 7 million children.
For their new population-based study, researchers from the Mayo Clinic in Rochester, MN, built on previous research they reported in 2013, in which they showed childhood asthma is linked to higher risk of developing shingles.
Effect of asthma on immunity 'may go beyond the airways'
Lead author Dr. Young Juhn, a pediatrician and asthma epidemiologist who heads a Mayo lab investigating the effect of asthma, allergic rhinitis and eczema on the risk of emerging or re-emerging infectious and chronic diseases, says:
"The effect of asthma on the risk of infection or immune dysfunction might very well go beyond the airways."
For their study, the Mayo team reviewed medical records from adults aged 50 and over living in Olmsted County, MN. They compared the frequency of asthma in 371 cases diagnosed with shingles against 742 matched cases without a history of shingles (controls).
The average age of the patients in the shingles group was 67 years. They were matched by birthday and sex to the controls. Of the 371 shingles patients, 87 (23%) had asthma, compared with 114 of the 742 (15%) controls.
Using a statistical method called logistic regression, the researchers calculated that adults with asthma appeared to have a 70% higher risk of developing shingles, compared with those without asthma.
They also found a link between atopic dermatitis and a higher risk of shingles, which occurred at a rate of 12% in patients with atopic dermatitis versus 8% of the controls.
While the team did not investigate the underlying mechanism that could link asthma or dermatitis with shingles, impaired immune function in the skin or airways is well documented in patients with these conditions.
They suspect that because asthma helps suppress immunity, it may increase the risk of reactivating the varicella zoster virus.
The researchers found no link between use of inhaled corticosteroids and raised risk of shingles, and they did not find a link between zoster vaccination and raised risk of shingles - rather, they found zoster vaccination was tied to a lower risk.
Dr. Juhn concludes:
"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 as a target group for zoster vaccination."