Day-to-day variability in nap duration predicts medical morbidity in older adults.

OBJECTIVE The objectives for the present study were to (a) examine within-person variability of nap duration and (b) assess how variability in nap duration is related to the number of health conditions in a sample of older adults. For highly variable behaviors such as sleep, it is important to consider fluctuations within the person instead of solely comparing averages of behaviors across persons. METHOD Data were drawn from a previous study examining sleep in 103 community-dwelling older adults. Subjective estimates of napping behavior were obtained from sleep diaries and objective estimates of napping behavior were obtained using actigraphy. Both measures were collected for 14 consecutive days. The sampled data were aggregated in terms of (a) average daily time spent napping and (b) average within-person fluctuations in daily nap duration. The health measure consisted of the number of self-reported health conditions. RESULTS Both the objective and subjective measures revealed that there was considerable day-to-day fluctuation in nap duration and that variability in nap duration, not mean duration, uniquely predicted the number of health conditions, b = .03, b* = .26, t(100) = 2.71, p = .01. CONCLUSIONS Duration of napping in older adults is a highly variable behavior, fluctuating as much within- as between-persons. Furthermore, variability in nap duration from day to day is predictive of greater medical morbidity, suggesting that clinicians should assess for inconsistencies in nap behavior in addition to duration, frequency, and timing.