title: Individual variations in serum melatonin levels through time: implications for epidemiologic studies.
abstract: Melatonin, a marker for the circadian rhythm with serum levels peaking between 2AM and 5AM, is hypothesized to possess anti-cancer properties, making it a mechanistic candidate for the probable carcinogenic effect of circadian rhythm disruption. In order to weigh epidemiologic evidence on the association of melatonin with cancer, we must first understand the laboratory and biological sources of variability in melatonin levels measured in samples. Participants for this methodological study were men enrolled in the Prostate Lung Colorectal and Ovarian Cancer Screening Trial (PLCO). We measured serum melatonin levels over a five year period in 97 individuals to test if melatonin levels are steady over time. The Pearson correlation coefficient between two measures separated by 1 year was 0.87, while the correlation between two measures separated by 5 years was to 0.70. In an additional cross-sectional study of 292 individuals, we used Analysis of Variance to identify differences in melatonin levels between different lifestyle and environmental characteristics. Serum melatonin levels were slightly higher in samples collected from 130 individuals during the winter, (6.36±0.59 pg/ml) than in samples collected from 119 individuals during the summer (4.83±0.62 pg/ml). Serum melatonin levels were lowest in current smokers (3.02±1.25 pg/ml, p = 0.007) compared to never (6.66±0.66 pg/ml) and former (5.59±0.50 pg/ml) smokers whereas BMI did not significantly affect serum melatonin levels in this study. In conclusion, the high 5 year correlation of melatonin levels implies that single measurements may be used to detect population level associations between melatonin and risk of cancer. Furthermore, our results reiterate the need to record season of sample collection, and individual characteristics in order to maximize study power and prevent confounding.
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland, United States of America.
authors.forename: Leticia M
authors.initials: LM
authors.lastname: Nogueira
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland, United States of America.
authors.forename: Joshua N
authors.initials: JN
authors.lastname: Sampson
authors.affiliation: Cancer Prevention Institute of California, Fremont, California, United States of America.
authors.forename: Lisa W
authors.initials: LW
authors.lastname: Chu
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland, United States of America.
authors.forename: Kai
authors.initials: K
authors.lastname: Yu
authors.affiliation: Division of Urological Surgery, Washington University School of Medicine, St. Louis, Missouri, United States of America.
authors.forename: Gerald
authors.initials: G
authors.lastname: Andriole
authors.affiliation: Department of Environmental Health Sciences, University of Minnesota School of Public Health, Minneapolis, Minnesota, United States of America.
authors.forename: Timothy
authors.initials: T
authors.lastname: Church
authors.affiliation: Department of Obstetrics, Gynecology, and Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America.
authors.forename: Frank Z
authors.initials: FZ
authors.lastname: Stanczyk
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland, United States of America.
authors.forename: Jill
authors.initials: J
authors.lastname: Koshiol
authors.affiliation: Cancer Prevention Institute of California, Fremont, California, United States of America.
authors.forename: Ann W
authors.initials: AW
authors.lastname: Hsing
mesh_terms: D000368:Aged; D015992:Body Mass Index; D002940:Circadian Rhythm / Q000502:physiology*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008550:Melatonin / Q000037:antagonists & inhibitors / Q000097:blood*; D008875:Middle Aged; D009369:Neoplasms / Q000517:prevention & control; D017440:Photoperiod; D012307:Risk Factors; D012621:Seasons; D012907:Smoking / Q000009:adverse effects
chemical_list: D008550:Melatonin