The association between Alzheimer's disease and thyroid disease in Rochester, Minnesota.

To determine whether an association exists between Alzheimer's disease (AD) and thyroid disease, we carried out two studies in the population of Rochester, Minnesota. We reviewed medical records of a cohort of 198 women with histologically confirmed Hashimoto's thyroiditis (1935 to 1974) for evidence of subsequent dementia, applying the criteria used for dementia in a previous determination of incidence and prevalence rates in this population. From a total of 4,197 person-years of follow-up, eight cases of AD were diagnosed, whereas the expected number was 5.8. The standardized morbidity ratio was 1.37, which failed to reach statistical significance. The second study was a retrospective case-control comparison that sought any relationship between AD and all thyroid disorders, using a previously identified (1960 to 1979) AD cohort (N = 646) and their age- and sex-matched controls. For myxedema there was a positive association for AD without significance, whereas in Graves' disease there was a significant negative association for AD.