Asthma increases risk for hyperthyroidism, particularly after age 30

Patients with asthma had a higher risk for developing hyperthyroidism, especially those aged older than 30 years, according to a retrospective study published in The Journal of Allergy and Clinical Immunology: In Practice.

Previous studies have indicated that hyperthyroidism exacerbates asthma, but Shuo-Yan Gau, of Chung Shan Medical University in Taiwan, and colleagues designed their study to assess the influence of asthma on hyperthyroidism.

Researchers used 1997 to 2013 data from the Longitudinal Health Insurance Database 2000 in Taiwan to evaluate 22,591 patients with asthma and an equal number of matched controls.

Patients with asthma had a higher cumulative probability for hyperthyroidism compared with controls (adjusted HR = 1.31; 95% CI, 1.12-1.53). The incidence rate per 100,000 person-months for hyperthyroidism in patients with asthma was 16.95 (95% CI, 15.31-18.78) compared with 12.88 (95% CI, 11.44-14.5) among the controls.

The researchers also found that patients with asthma had a higher rate than the controls for visits to hospital departments — such as pediatrics, family medicine, general medicine and otolaryngology — related to an asthma diagnosis.

The multivariable model that included the amount of these hospital visits also showed an increased risk for hyperthyroidism in the asthma cohort, with an aHR of 1.22 (95% CI, 1.02-1.45).

The risk for hyperthyroidism increased among the patients with asthma who had a short follow-up time, such as less than 36 months (aHR = 1.59; 95% CI, 1.25-2.03), and for those aged older than 30 years compared with younger patients (age 30-44 years, aHR = 1.49; 95% CI, 1.05-2.11; age 45-64 years, aHR = 1.33; 95% CI, 1.04-1.71; age 65 years, aHR = 1.52; 95% CI, 1.06-2.18).

Based on sensitivity analyses that excluded incidents of hyperthyroidism events within 6, 12 and 18 months from baseline to control for bias due to reverse causation, all three models showed a significant risk for hyperthyroidism among the patients with asthma (19.9%-23.8%) compared with controls.

Gau and colleagues wrote that lifestyle could influence the increased risk for hyperthyroidism among the older population.

“For instance, exposure to air pollutants could influence thyroid function more often in the older population than in the younger population,” they wrote.

The researchers noted limitations in the study related to potential bias in the form of possible unknown confounders, reports of short-term risk, and complications with surveillance and diagnostic codes.

“Clinicians caring for patients with asthma should be aware of the increased risk of future development of hyperthyroidism in their patients,” Gau and colleagues concluded.