Hypothyroidism and risk of mild cognitive impairment in elderly persons: a population-based study.

IMPORTANCE An association of clinical and subclinical hypothyroidism with mild cognitive impairment (MCI) has not been established. OBJECTIVE To evaluate the association of clinical and subclinical hypothyroidism with MCI in a large population-based cohort. DESIGN, SETTING, AND PARTICIPANTS A cross-sectional, population-based study was conducted in Olmsted County, Minnesota. Randomly selected participants were aged 70 to 89 years on October 1, 2004, and were without documented prevalent dementia [CORRECTED]. A total of 2050 participants were evaluated and underwent in-person interview, neurologic evaluation, and neuropsychological testing to assess performance in memory, attention/executive function, and visuospatial and language domains. Participants were categorized by consensus as being cognitively normal, having MCI, or having dementia according to published criteria. Clinical and subclinical hypothyroidism were ascertained from a medical records linkage system. MAIN OUTCOMES AND MEASURES Association of clinical and subclinical hypothyroidism with MCI. RESULTS Among 1904 eligible participants, the frequency of MCI was 16% in 1450 individuals with normal thyroid function, 17% in 313 persons with clinical hypothyroidism, and 18% in 141 individuals with subclinical hypothyroidism. After adjusting for covariates (age, educational level, sex, apolipoprotein E ε4, depression, diabetes mellitus, hypertension, stroke, body mass index, and coronary artery disease) we found no significant association between clinical or subclinical hypothyroidism and MCI (odds ratio [OR], 0.99 [95% CI, 0.66-1.48] and 0.88 [0.38-2.03], respectively). No effect of sex interaction was seen on these effects. In stratified analysis, the odds of MCI with clinical and subclinical hypothyroidism among men was 1.02 (95% CI, 0.57-1.82) and 1.29 (0.68-2.44) and, among women, was 1.04 (0.66-1.66) and 0.86 (0.37-2.02), respectively. CONCLUSIONS AND RELEVANCE In this population-based cohort of elderly people, neither clinical nor subclinical hypothyroidism was associated with MCI. Our findings need to be validated in a separate setting using the published criteria for MCI and confirmed in a longitudinal study.