Objectives: 

Circadian rhythms are involved in many physiological and behavioral processes. Several epidemiological studies provided evidence of a nycthemeral rhythm of sexual activity in young stable couples. However, previous studies used small sample sizes and all were preformed in the EEUU. The present study sought to verify this circadian rhythmicity in a regular sized sample of young European adults and to identify environmental factors responsible for the rhythm of their sexual activity

Materials: 

100 university students has been interviewed (50 men and 50 women, unrelated between them) aged between 20 and 25 years, all with a regular partner. Subjects were asked three main questions: 1) the most frequent time for sexual activity, 2) the reasons by which they decided their time for sex and 3) when they felt more eager for sex.

Results: 

No differences were found between men and women in sexual activity time, showing a significant peak around 11-12 pm. The activity was correlated with the time of higher sexual desire, but also with possibility and opportunity. Regarding the desire, males peaked around 08-09 am and 11-12 p.m., while women showed a single peak around 11-12 pm.

Conclusions: 

In conclusion, although it is currently affirmed that human adults seem to find opportunities for sex at any time, most sexual activity occurs around bedtime, in agreement with other similar studies. The sexual desire between men could respond to an endogenous 8h ultradian rhythm although no significant peak was observed at 16 pm. This rhythm was masked by a strong environmental influence, mainly due to the availability of time and place. On the other hand, females could show a single robust circadian pattern also masked by possibility and opportunity.