Diurnal cycles of salivary cortisol in older adults

Cortisol has a well-documented circadian pattern. However, recent studies have demonstrated that individual variation in diurnal cortisol patterns occurs in young adult populations. Since older adults experience altered sleep-wake cycles and changes in circadian rhythmicity, we may see even greater variations in diurnal cortisol patterns in older adults. This study examined salivary cortisol patterns in 48 community dwelling older adults. Participants (mean age 76+/-6) collected saliva every 2 h over a three-day period. Cortisol was assayed by using RIA. Cortisol cycles were defined as inconsistent, typical or flat based on the slopes of two sequential daily cortisol patterns. Demographic, physical, psychological and behavioral measures were tested for group differences using t-tests and chi-square analyses. Forty-eight percent of the sample had inconsistent cycles, 50% had typical cycles and 2% had flat cycles. This sample had a higher percentage of inconsistent cycles and fewer flat cycles than reported for young adults (p=0.008) (Psychoneuroendocrinology 22 (1997) 89). Those with inconsistent cycles were younger and reported higher caffeine and food intake than those with typical cycles. This study demonstrates that normal diurnal rhythms of cortisol can be maintained in older adults, while day-to-day variation may increase.