P101. The influence of sex and age on melatonin suppression by warm-white light (K 2883 K)

Abstract

Introduction In the past, the suppression of the pineal hormone melatonin by light has been investigated in several studies, frequently using small samples and only male subjects. Whereas the nocturnal melatonin production is thought to decrease with age, our knowledge about the extent of the light-induced melatonin suppression depending on sex and age is only limited. Our study addressed this issue in more details. Methods Subjects for this study were pre-screened for the onset of melatonin production in the evening hours. In total, 94 healthy subjects between 18 and 73 years were enrolled (42 men/52 women). All of them had a regular sleep-wake schedule and were morning or intermediate types according to the Ostberg-Horne-Ostberg morningness-eveningness questionnaire (scores: 41–73). They completed 4 evening laboratory sessions (19:00–23:00 h) predominantly in a weekly interval. The light protocol for each session consisted of a 2-h dim light ( Results After 2 h of dim-light condition all enrolled study participants showed an increase in melatonin production versus baseline of different magnitude. One hour of warm-white light at 500 lx (0.264 W/m2) caused very variable suppression of melatonin which did not exceed about 64% in both sexes. The average melatonin suppression over all subjects was 30.2% with sex related differences in the frequency of strong suppression, being higher in men. The inter-individual variability in melatonin suppression by warm-weight light was not related to the age of study participants. We also proved the impact of physical activity. Men with low physical activity showed relatively small plasma melatonin concentrations after 2 h dim-light condition, but a high sensitivity to the warm-white light applicated. Conclusions The obvious individual variability in the sensitivity of melatonin production for artificial light in the evening with possible sex but not clear and simple age related differences could be a critical factor in our understanding of light effects. Levels of physical activity in the leisure time could be a masking factor which should be adequately controlled in similar studies.