Does sleep predict next-day napping or does napping influence same-day nocturnal sleep? Results of a population-based ecological momentary assessment study.

The temporal relationship between nocturnal sleep and daytime napping has only been assessed in small non-representative samples, and suggests that nocturnal sleep and napping are interdependent, although mixed results exist. In this study, we investigated the temporal relationship between nocturnal sleep and napping (and vice versa). A population-based sample of middle-aged adults (N = 683, mean age 60.7 [SD 9.5]) completed seven days of ecological momentary assessment reporting sleep and nap characteristics. Multilevel random-effects models were used to assess the temporal relationship between sleep duration and quality, and nap occurrence and duration (and vice versa). In sum, 64% of the study population took at least one nap over the course of seven days. Poor subjective sleep quality and shorter sleep duration increased the likelihood and duration of next-day napping. No effect of nap occurrence or duration was found on same-day nocturnal sleep duration and quality. However, when considering the timing of nap, afternoon naps, but not morning or evening naps, decreased same-day nocturnal sleep duration. Naps seem to compensate for poor subjective sleep quality, and to some extent for short sleep duration. As only afternoon naps reduced same-day nocturnal sleep duration, timing of the daytime nap seems to matter with respect to same-day nocturnal sleep duration