Sexual orientation and the sleep-wake cycle: a preliminary investigation.

The sleep-wake cycle as a function of sexual orientation was investigated. Male and female, heterosexual and homosexual subjects completed a sexual-orientation questionnaire and four sets of recording sheets of activities for a 16-day period. Mean sleep duration was calculated from the record sheets using waking-up and going-to-sleep times. It was predicted that homosexual males and females would awake earlier, go to sleep later, and thus have shorter sleep duration compared to heterosexuals. This was supported by the results. Although a sexual orientation by sex interaction just failed to reach significance, additional analyses of the results indicated that differences in sleep duration between heterosexuals and homosexuals were markedly related to sex. The possibility that these results reflect dimorphic features of the human supra-chiasmatic nucleus (SCN) is discussed.