People with subclinical hyperthyroidism are at 34% greater risk of experiencing a fracture compared with those with normal thyroid function, new research shows.
The finding, from a study of nearly 11,000 middle-aged men and women followed for a median of 2 decades, “highlights a potential role for more aggressive screening and monitoring of patients with subclinical hyperthyroidism to prevent bone mineral disease,” the researchers wrote.
Primary care physicians “should be more aware of the risks for fracture among persons with subclinical hyperthyroidism in the ambulatory setting,” Natalie R. Daya, a PhD student in epidemiology at Johns Hopkins Bloomberg School of Public Health, Baltimore, and first author of the study, told this news organization.
Ms. Daya and her colleagues published their findings in JAMA Network Open.
Building on earlier findings
The results agree with previous work, including a meta-analysis of 13 prospective cohort studies of 70,289 primarily White individuals with an average age of 64 years, which found that subclinical hyperthyroidism was associated with a modestly increased risk for fractures, the researchers noted.
“Our study extends these findings to a younger, community-based cohort that included both Black and White participants, included extensive adjustment for potential confounders, and had a longer follow-up period (median follow-up of 21 years vs. 12 years),” they wrote.
The study included 10,946 participants in the Atherosclerosis Risk in Communities Study who were recruited in Washington County, Maryland; Forsyth County, North Carolina; Jackson, Mississippi; and the suburbs of Minneapolis.
Baseline thyroid function was measured in blood samples collected during the second visit, which occurred between 1990 and 1992. No participants in the new analysis took thyroid medications or had a history of hospitalization for fractures at baseline, and all identified as Black or White. The mean age was 57 years, 24% were Black, and 54.3% were female.
Subclinical hyperthyroidism was defined as a thyrotropin level less than 0.56 mIU/L; subclinical hypothyroidism as a thyrotropin level greater than 5.1 mIU/L; and normal thyroid function as a thyrotropin level between 0.56 and 5.1 mIU/L, with normal free thyroxine levels of 0.85-1.4 ng/dL.
The vast majority (93%) of participants had normal thyroid function, 2.6% had subclinical hyperthyroidism, and 4.4% had subclinical hypothyroidism, according to the researchers.
Median follow-up was 21 years. The researchers identified 3,556 incident fractures, detected with hospitalization discharge codes through 2019 and inpatient and Medicare claims data through 2018, for a rate of 167.1 per 10,000 person-years.
Adjusted hazard ratios for fracture were 1.34 (95% confidence interval [CI], 1.09-1.65) for people with subclinical hyperthyroidism and 0.90 (95% CI, 0.77-1.05) for those with subclinical hypothyroidism, compared with those with normal thyroid function.
Most fractures occurred in either the hip (14.1%) or spine (13.8%), according to the researchers.
Limitations included a lack of thyroid function data during the follow-up period and lack of data on bone mineral density, the researchers wrote.