Lack of seasonal variation in the births of patients with dementia of the Alzheimer type.

Seasonal variation in the birth rates of patients suffering from dementia of the Alzheimer type (DAT) was investigated in 150 patients, aged 42-88 years, and in 132 normal control subjects of comparable age and gender. No seasonal variation or cyclic trend could be demonstrated in the DAT patients compared with control subjects. The exclusion from the analysis of the patients with a positive family history did not change the results of the study, which further suggests that a seasonality in DAT birth rates is unlikely.