The interactive effects of nocturnal sleep and daytime naps in relation to serum C-reactive protein

Abstract

Background C-Reactive Protein (CRP) is a general marker of inflammation that has been differentially linked with sleep. Elevated CRP (i.e., high inflammation) has been associated with either short/insufficient sleep duration, long sleep duration, both, or neither. Daytime napping has also been tied to increased and decreased inflammation. We sought to unify these findings by examining the relationship between CRP and sleep duration in conjunction with napping in a healthy young adult cohort. Participants Young adults (mean age = 29.05 yrs, n = 2,147) from the National Longitudinal Study of Adolescent Health (Add Health) cohort, a nationally representative longitudinal sample. Methods/Results ANCOVA tests examined whether self-reported sleep duration (Short, Medium or Long) and nap frequency (none-few days/week; most days/week; every day) interacted in relation to CRP. Standard covariates (i.e., age, gender, race/ethnicity, body mass index, physical activity, depression, snoring, systolic blood pressure, clinical symptoms, household income) were used. There was a linear increase in CRP with increased napping (contrast estimate = .265, 95% CI [.045 to .485], p = .018). There was also an interaction between sleep duration and napping frequency in relation to CRP (F4,2128 = 2.90, p = .021). Inflammation differed between nap groups within the long and short sleep groups. Conclusions Our results suggest increased napping is an independent predictor of inflammation in young adults. These results also provide evidence for interactive effects of inflammation, nocturnal sleep, and daytime naps. Our findings confirm that excess sleep, insufficient sleep, frequent napping and infrequent napping can all be linked with elevated CRP, but these relationships depend on both nocturnal and daytime sleep patterns. These analyses will guide future work to more specifically examine sleep-inflammation processes and directionality.

Poor sleep moderates the relationship between daytime napping and inflammation in Black and White men

“…We did not find a main effect of napping with inflammation. However, consistent with previous work (21), results revealed that actigraphy-assessed aspects of sleep moderated the association between actigraphy-assessed napping and IL-6. More napping was associated with higher IL-6 among men who had short sleep duration, low sleep efficiency, or poor perceived sleep quality.…”

“…More napping was associated with higher IL-6 among men who had short sleep duration, low sleep efficiency, or poor perceived sleep quality. Together, our results and those of Mantua and Spencer (21) raise the possibility that short sleep may not be “corrected” by napping and it may be better to lengthen sleep duration.…”

“…In older adults, one study reported a positive association between self-reported daily napping and CRP, particularly among those who reported spending either the fewest or the most hours in bed at night (19); however, a second study reported no association between self-reported napping and circulating levels of IL-6 (20). In young adults (mean age = 29 years), evidence suggested a positive association between self-reported nap frequency across the past week and CRP, particularly among those who napped every day and slept short (< 5 hours) at night (21). Finally, in a sample of healthy high school students, more actigraphy-assessed proportion of days napped across a weeklong study period was associated with elevated serum IL-6 but not CRP; though, notably, almost all students in this study had short nocturnal sleep (22).…”

Napping: A public health issue. From epidemiological to laboratory studies

“…199 The mid-afternoon circadian dip could also be seen as an evolutionary opportunity to encourage a midday nap, leading to the possibility of reducing nighttime sleep. This raises the question as to whether the midday nap could be a sleep surrogate that could explain why some subjects who restrict their nocturnal sleep time and usually practice a daytime nap seem to not suffer much from the consequences of sleep debt 178 . Space study simulations, although they can hardly be extended to the general population, suggest that splitting sleep into several sequences (polyphasic sleep) does not strongly disrupt cognitive performance, sleepiness, or inflammatory responses to sleep deprivation.…”

“…177 The authors reported that for night sleep durations of between 5 and 9 hours, regardless of the napping frequency, CRP levels were relatively low. 178 However, when looking at the short sleep group (< 5 hours of night-time sleep), the subjects who reported napping every day had significantly higher CRP levels than the group that napped M A N U S C R I P T…”