Subclinical Hypothyroidism and Indices for Metabolic Syndrome in Japanese Women: One-Year Follow-Up Study

Abstract

Subclinical hypothyroidism (SCH) and metabolic syndrome (MetS) increase with age; however, their relationship remains unclear. Our objective was to investigate the relationship between SCH and indices of metabolic syndrome and follow up subjects for 1 year. Cross-sectional and longitudinal follow-up studies of cases were collected from Takasaki Hidaka Hospital between 2003 and 2007. Overall, 11 498 participants of health checkups were analyzed. The mean age was 48 ± 9 years. The relationship between SCH and indices of MetS were examined. Serum free T4 levels were lower in women than men in most of the age groups, and the prevalence of SCH, 6.3% in women vs 3.4% in men, increased with age, reaching 14.6% in 70-year-old women. Multivariate logistic-regression analyses revealed that waist circumference and the serum triglyceride and low-density lipoprotein-cholesterol levels were significantly higher in subjects with SCH than without among women. Reflecting these findings, the adjusted odds ratio of MetS in patients with SCH was higher than in the euthyroid subjects in women with an odds ratio of 2.7 (95% confidence interval 1.1-5.6; P = .017) but not in men. Furthermore, progression from euthyroid into SCH resulted in a significant increase in the serum triglyceride levels but not low-density lipoprotein-cholesterol in women. Japanese women exhibited a high prevalence of SCH associated with low free T4 levels. There was a strong association between SCH and several indices of metabolic syndrome in women. SCH may affect serum triglyceride levels and be a risk factor for metabolic syndrome.