Women in the study were 3 times more likely to be affected by rheumatoid arthritis (RA) and nearly 4 times more likely to develop hypothyroidism, compared with men.
The retrospective cohort study also found the risk to be even greater in women and patients aged 60 and older.
RA is known to be more prevalent in women than men, and past studies have continued to demonstrate the increased risk of developing hypothyroidism among people with RA. However, the role of comorbidities in hypothyroidism development has not been evaluated.
Using the Taiwan National Health Insurance Research Database, researchers collected data on 16,714 patients who received a RA diagnosis between 2000 and 2008, matching by sex, age, and index year to a control group of 66,856 individuals without RA. All patients were over age 20, with the mean age being 51.7 in the RA group and 51.4 in the control group.
Women included in the study were affected by RA 3 times more often compared with men, and made up approximately 75% of the total study population. The authors also noted that the RA group had more blue-collar workers and rural residents compared with the control group.
The authors found that hypothyroidism incidence was 1.74 times higher in patients with RA than patients without RA (adjusted hazard ratio [aHR], 1.67; 95% CI, 1.39-2.00). Based on sex, women with RA were 3.6 times more likely to develop hyperthyroidism compared with men, and women in the control group still had a higher incidence than men without RA.
“Therefore, the mechanism associating with hormonal abnormality for both RA and the development of hypothyroidism may be valid,” the authors said.
RA development has been linked to inflammation and proinflammatory cytokines, the latter of which are involved in the pathogenesis of RA and atherosclerosis—a thickening or hardening of the arteries caused by plaque buildup—and growing evidence has shown a higher prevalence of related comorbid disease.
“In our study, most baseline comorbidities were more prevalent in the RA cohort than in the controls, with the exception of DM [diabetes] and hyperlipidemia,” the authors wrote. “Factors associated with RA and associated comorbid diseases may underlie the association between RA and hypothyroidism.”
Hypothyroidism incidence also increased with age. In individuals with RA aged 20 to 39, incidence was 12.1 per 1000 person years, while incidence was 20 per 1000 person years in those aged 60 and older. Both age groups saw a higher incidence among those with RA compared with those without RA.
The researchers also measured how comorbidities were related to incidence. All comorbidities—hypertension, ischemic heart disease, stroke, diabetes, hyperlipidemia, and chronic kidney disease—were associated with an increased hyperthyroidism incidence in both groups, but significantly higher in the RA group. They found that stroke had the strongest association in the RA group (aHR, 3.85; 95% CI, 1.24-12.0).
The findings further support the association between autoimmune disease and the development of hypothyroidism, and the authors said closely monitoring RA patients and timely intervention could improve the prognosis of those who develop hypothyroidism.
“Further study may consider the treatment of using biological antirheumatic agents, comparing with nonsteroidal anti-inflammatory drugs and disease-modifying antirheumatic drug,” the authors said.
Huang CM, Sung FC, Chen HJ, Lin CC, Lin CL, Huang PH. Hypothyroidism risk associated with rheumatoid arthritis: A population-based retrospective cohort study. Medicine. Published online January 7, 2022. doi:10.1097/MD.0000000000028487