Prevalence and multimorbidity patterns of thyroid dysfunction in Chinese adults

The risk of thyroid dysfunction (TD) persists in the Chinese population. However, large-scale epidemiological studies investigating TD prevalence and its geographic disparities are limited. Previous studies have mostly focused on associations between TD and individual organ systems or single medical conditions. This nationwide, large-scale study utilized data from the Meinian Health Check-up database across all 31 provinces of the Chinese mainland. A total of 10,748,391 adults who had health check-ups between 2017 and 2023 and had complete thyroid function results for serum thyroid-stimulating hormone, free triiodothyronine, and free thyroxine were included. TD was categorized into four groups: overt hyperthyroidism (OHyper), subclinical hyperthyroidism (SHyper), overt hypothyroidism (OHypo), and subclinical hypothyroidism (SHypo). The weighted prevalence of TD was calculated, and its associations with 21 medical conditions across various organ systems were assessed. The weighted prevalences were 0.76% (95% CI, 0.73%-0.79%) for OHyper, 0.82% (0.79%-0.85%) SHyper, 0.58% (0.54%-0.61%) OHypo, and 8.27% (8.00%-8.54%) SHypo. TD was more prevalent in women, older adults (except for OHyper), and individuals who resided in cities with lower gross domestic product levels. Notable geographic disparities were observed, with SHyper prevalence higher in coastal regions and both OHypo and SHypo being more widely spread in inland regions. TD was associated with a broad spectrum of medical conditions. Specifically, hyperthyroidism was primarily linked to fast heart rate, abnormal liver enzymes, decreased high-density lipoprotein-cholesterol, and hyperglycemia. In contrast, hypothyroidism was more closely associated with abnormal liver enzymes, impaired renal function, dyslipidemia, obesity, and fatty liver. Sex-specific differences were exhibited for the association between subclinical TD and atherogenic markers (increased carotid intima-media thickness and presence of carotid plaques). SHypo is highly prevalent, and TD distribution shows considerable demographic, geographic, and socioeconomic variation. TD is more likely to coexist with systemic multimorbidity. These findings highlight the importance of continued TD surveillance and patient-centered, multidisciplinary management strategies at the health system level in China. This study serves as a valuable complement to nationally representative studies by using existing big data resources to enable rapid and cost-effective insights into TD distribution and its multimorbidity cluster.