Objective: We tested the hypothesis that exposure to room light in the late evening suppresses the onset of melatonin synthesis and shortens the duration of melatonin production.Design: In a retrospective analysis, we compared daily melatonin profiles in individuals living in room light (Ͻ200 lux) vs. dim light (Ͻ3 lux).Patients: Healthy volunteers (n ϭ 116, 18 -30 yr) were recruited from the general population to participate in one of two studies.Setting: Participants lived in a General Clinical Research Center for at least five consecutive days.Intervention: Individuals were exposed to room light or dim light in the 8 h preceding bedtime.Outcome Measures: Melatonin duration, onset and offset, suppression, and phase angle of entrainment were determined.Results: Compared with dim light, exposure to room light before bedtime suppressed melatonin, resulting in a later melatonin onset in 99.0% of individuals and shortening melatonin duration by about 90 min. Also, exposure to room light during the usual hours of sleep suppressed melatonin by greater than 50% in most (85%) trials.Conclusions: These findings indicate that room light exerts a profound suppressive effect on melatonin levels and shortens the body's internal representation of night duration. Hence, chronically exposing oneself to electrical lighting in the late evening disrupts melatonin signaling and could therefore potentially impact sleep, thermoregulation, blood pressure, and glucose homeostasis. Endocrinology & Metabolism, published December 30, 2010, 10.1210/jc.2010-2098 Context: Timing of menopause is largely influenced by genetic factors. Because menopause occurs when the follicle pool in the ovaries has become exhausted, genes involved in primordial follicle recruitment can be considered as candidate genes for timing of menopause.
This article appears in The Journal of Clinical
Genes Involved in Initial FollicleObjective: The aim was to study the association of 23 tagging single nucleotide polymorphisms in five genes (AMH, AMHR2, BMP15, FOXL2, and GDF9) involved in recruitment of the primary follicle pool, including the AMHR2 gene, which has recently been associated with age at menopause.Design: We conducted a cross-sectional association study. Setting and Participants: We studied a population-based sample of 3616 Dutch women with natural menopause.Main Outcome Measure: We measured age at natural menopause.Results: Both studied AMHR2 tagging single nucleotide polymorphisms (rs2002555 and rs11170547) in the AMHR2 gene were associated with age at natural menopause in interaction with parity. Parous rs2002555 G/G carriers had menopause 1 yr later compared with A/A carriers (P ϭ 0.01). For rs11170547, each minor allele (T) was associated with a 0.41-yr later onset of menopause in parous women (P ϭ 0.01). Additionally, rs6521896 in BMP15 was associated with later menopause ( ϭ 0.41; P ϭ 0.007). Variants in the AMH, FOXL2, and GDF9 genes were not associated with timing of menopause.Conclusions: The present study confirms an earlier finding that var...
