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Sex differences in circadian rhythms have been reported with some conflicting results. The timing of sleep and length of time in bed has not been considered, however, in previous such studies. The current study has three major aims: (1) replicate previous studies in a large sample of young adults for sex differences in sleep patterns and dim light melatonin onset (DLMO) phase; (2) in a subsample constrained by matching across sex for bedtime and time in bed, confirm sex differences in DLMO and phase angle of DLMO to bedtime; (3) explore sex differences in the influence of sleep timing and length of time in bed on phase angle. Three hundred and fifty-six (207 women) first year Brown University students ages 17.7–21.4 (mean=18.8, sd=.4) years were included in these analyses. Wake time was the only sleep variable that showed a sex difference. DLMO phase was earlier in women than men and phase angle wider in women than men Shorter time in bed was associated with wider phase angle in women and men. In men, however, a three way interaction indicated phase angles were influenced by both bedtime and time in bed, a complex interaction was not found for women. These analyses in a large sample of young adults on self-selected schedules confirm a sex difference in wake time, circadian phase, and the association between circadian phase and reported bedtime. A complex interaction with length of time in bed occurred for men but not women. We propose that these sex differences likely indicate fundamental differences in the biology of the sleep and circadian timing systems as well as in behavioral choices.

We observed how sailors manage their sleep and alertness before and during competition in a long-haul yacht race. Global performance of the teams was also recorded. We assessed eight sailors aged 21-30 years, split into four teams, who competed in the Tour de France à la Voile 2002 yacht race. Two phases of the race were examined: two legs in both the Atlantic Ocean and Mediterranean Sea. Sleep length, sleep debt, and sleepiness before competition and on board during the race were assessed using ambulatory polysomnography. Intermediate and final rankings were considered as a reflection of performance. A significant correlation was observed between the sleep debt before competition and the total sleep time on board during the Atlantic legs. The greater the sleep debt, the more sleepy the participants were. During the Mediterranean legs, almost all the sailors were deprived of sleep and slept during the daytime competitions. We observed that the final ranking in the race related to the sleep management strategy of the participants. In extreme competitive conditions, the effect of a good night's sleep before competition on performance is important. The strategy of the winners was to get sufficient sleep before each leg so as to be the most alert and efficient during the race.

Objectives We hypothesized that shorter sleep durations and greater variability in sleep patterns are associated with weight gain in the first semester of university. Methods Students (N=132) completed daily sleep diaries for 9-weeks, completed the MEQ (chronotype) and CES-D (depressed mood) at week9, and self-reported weight/height (weeks 1&9). Mean and variability scores were calculated for sleep duration (TST,TSTv), bedtime (BT,BTv), and wake time (WT,WTv). Results An initial hierarchical regression evaluated (block1) sex, ethnicity; (block2) depressed mood, chronotype; (block3) TST; (block4) BT, WT; and (block5; R2change=0.09, p=0.005) TSTv, BTv, WTv with weight change. A sex-by-TSTv interaction was found. A final model showed that ethnicity, TST, TSTv, and BTv accounted for 31% of the variance in weight change for males; TSTv was the most significant contributor (R2 change=0.21, p<0.001). Conclusions Daily variability in sleep duration contributes to males’ weight gain. Further investigation needs to examine sex-specific outcomes for sleep and weight.

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