Seasonal effects on cortisol secretion in normal aging, mild cognitive impairment and Alzheimer's disease.

Previous studies found higher cortisol levels in Alzheimer's disease (AD) compared to normal elderly controls (NCs). However, studies on individuals with mild cognitive impairment (MCI), who are at risk to progress to AD, are contentious. In this study, we examined whether seasonal variations in cortisol secretion in NCs, MCI individuals and AD patients might mask group differences in cortisol secretion. We found significant seasonal differences in salivary cortisol levels in all three groups. Moreover, by testing everyone in the same seasons, we found lower salivary cortisol levels in NCs compared to MCI individuals and AD patients. This suggests that controlling for the season of sampling may help elucidate subtle effects of normal and pathological aging on basal cortisol secretion.