Background: Dyslipidemia is an important global health problem, particularly in the elderly population. Traditionally, the high prevalence of dyslipidemia in elderly people is considered a "natural condition." Notably, subclinical hypothyroidism (SCH) is one of the most important risk factors for dyslipidemia. Few studies have assessed whether SCH plays a role in the increase in age-related dyslipidemia. This study aimed to explore the association between SCH and lipid profiles in different age groups.
Methods: This was a large-scale, population-based, case-control study. The population was derived from the REACTION study conducted across China. A total of 17,046 individuals (8827 cases and 8219 controls) aged 40 years or older were enrolled in the final analyses. The relationships between SCH and serum lipid parameters in each age group were evaluated after adjustment for thyroid hormones and common confounding factors.
Results: In the entire population, thyrotropin (TSH), the key indicator of SCH, was positively associated with cholesterol parameters (total cholesterol [TC] and low-density lipoprotein cholesterol [LDL-C]) through the sixth decade of life. After adjusting for common confounding factors and thyroid hormones, each 1 mIU/L increase in TSH was estimated to elevate the TC level by 0.0147 mmol/L and 0.0551 mmol/L, respectively, in individuals aged 40-49 years and 60-69 years. Similarly, with each 1 mIU/L increase in TSH, the LDL-C level tended to show gradually greater increases as age increased. In moderately old subjects (60-69 years), mild (TSH≤10 mIU/L) and significant (TSH>10 mIU/L) SCH increased the concentration of TC approximately 1.03- and 1.36-fold, and the concentration of LDL-C approximately 1.19- and 1.65-fold, respectively, when compared with younger subjects.
Conclusions: TSH exhibited a stronger effect on the TC and LDL-C level in moderately old subjects than in younger subjects. SCH might augment and worsen the effects of aging on serum lipid profiles.