Are age and sex effects on sleep slow waves only a matter of electroencephalogram amplitude?

Abstract

Aging is associated with reduced slow wave (SW) density (number SW/min in non-rapid-eye-movement sleep) and amplitude. It has been proposed that an age-related decrease in SW density may be due to a reduction in EEG amplitude instead of a decline in the capacity to generate SW. Here, we propose a data-driven approach to adapt SW amplitude criteria to age and sex. We predicted that the adapted criteria would reduce age and sex differences in SW density and SW characteristics but would not abolish them. A total of 284 healthy younger and older adults participated in one night of sleep EEG recording. We defined age- and sex-adapted SW criteria in a first cohort of younger (n=97) and older (n=110) individuals using a signal-to-noise ratio approach. We then used these age- and sex-specific criteria in an independent second cohort (n=77, 38 younger and 39 older adults) to evaluate age and sex differences on SW density and SW characteristics. After adapting SW amplitude criteria, we showed maintenance of an age-related difference for SW density whereas the sex-related difference vanished. Indeed, older adults produced less SW compared to younger adults. Specifically, the adapted SW amplitude criteria increased the probability of occurrence of low amplitude SW (<80µV) for older men especially. Our results thereby confirm an age-related decline in SW generation rather than an artefact in the detection amplitude criteria. As for the SW characteristics, the age- and sex-adapted criteria display reproducible effects across the two independent cohorts suggesting a more reliable inventory of the SW.

Sleep Measurements in Women

“…27 With increasing age, studies show less delta activity in women compared with men, 27 although there is also contrasting evidence showing women having less deficits in SWS, exhibited by more total minutes in this stage, and less reduced SWS proportions, transition probabilities, and durations as compared with men. 28 As applying age-and sex-adapted SWS criteria to sleep scoring seems to counteract the effect of sex, 29 there is the possibility that age has a stronger effect on sleep variables than sex. 27,29 Measures of sleep apnea also show sex differences, with women exhibiting lower AHI and ODI, more partial occlusion, higher REM-AHI, and less supine AHI.…”

“…28 As applying age-and sex-adapted SWS criteria to sleep scoring seems to counteract the effect of sex, 29 there is the possibility that age has a stronger effect on sleep variables than sex. 27,29 Measures of sleep apnea also show sex differences, with women exhibiting lower AHI and ODI, more partial occlusion, higher REM-AHI, and less supine AHI. [21][22][23][24]27,97,98 Mechanistic explanations for the sleep and sleep apnea differences between sexes have been suggested, such as age, differences in circadian rhythm, and hormones 19 and for OSA, also other factors such as anatomy.…”

“…To date, there are also no differences in setup of recording or scoring depending on sex, 11,30 and in addition, it is not elucidated whether or not differences in physical characteristic (for instance skull characteristics 31 ) may contribute to differences in signals. Data from Rosinvil and colleagues showed that including sex and also age in their model predictions affected the recorded/analyzed signal (SWS) 29 and that from Yetton and colleagues 28 showed an apparent interaction between sex and age. At least when it comes to the scoring of sleep and sleep-related variables, this raises the important issue of whether or not different scoring criteria should be applied in different groups.…”

“…In contrast to previous studies showing sex differences, Rosinvil and colleagues showed that when applying the sex-and age-adapted SWS criteria, sex differences vanished, whereas age differences maintained. 29 The set up for PSG, PG, and actigraphy, respectively, does not specify any differences for women as opposed to men, and scoring criteria are not different between sexes. 11,30 To our knowledge, no studies have assessed whether setup should be different for men and women.…”

Circadian Rhythms, Sleep, Immunity, and Fragility in the Elderly: The Model of the Susceptibility to Infections

“…Indeed, women present sharper and steeper SW compared with men. The production of flatter slopes of SW rather than sudden SW slope (200 µV/s) is more frequently observed in older man compared with older women (10). During young adulthood, women reach both puberty and their peak eveningness more precociously compared with men.…”