title: The evidence for seasonal variations of testosterone in men.
abstract: Ample evidence exists to support the concept of diurnal variations in testosterone levels; however, substantiation for seasonal fluctuations is sparse and inconsistent. Since circadian disparities exist, laboratory screening for hypogonadism has traditionally been conducted using serum testosterone levels obtained in the early morning. Should circannual variability of testosterone be confirmed, it would make the monitoring of testosterone levels more difficult while forcing the development of seasonal reference standards to allow for comparison. Moreover, decisions to begin treatment and adjustment of practice patterns would likely follow. This review thoroughly explores all of the available evidence concerning seasonal variations in testosterone levels. The impacts of melatonin, vitamin D, sleep-wake cycles, light exposure, physical activity, BMI, and waist circumference are also discussed. Current research suggests that while some evidence exists to support the notion of seasonal testosterone variations, the discussed inconsistencies preclude the incorporation of this concept into current clinical standards.
authors.affiliation: Scott Department of Urology, Baylor College of Medicine, Houston, TX, United States. Electronic address: rpsmith@bcm.edu.
authors.forename: Ryan P
authors.initials: RP
authors.lastname: Smith
authors.affiliation: Scott Department of Urology, Baylor College of Medicine, Houston, TX, United States.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Coward
authors.affiliation: Scott Department of Urology, Baylor College of Medicine, Houston, TX, United States.
authors.forename: Jason R
authors.initials: JR
authors.lastname: Kovac
authors.affiliation: Scott Department of Urology, Baylor College of Medicine, Houston, TX, United States. Electronic address: larryl@bcm.edu.
authors.forename: Larry I
authors.initials: LI
authors.lastname: Lipshultz
mesh_terms: D015992:Body Mass Index; D002940:Circadian Rhythm / Q000502:physiology; D006801:Humans; D007006:Hypogonadism / Q000097:blood / Q000175:diagnosis; D008297:Male; D008550:Melatonin / Q000097:blood; D009043:Motor Activity / Q000502:physiology; D012621:Seasons; D012890:Sleep / Q000502:physiology; D013472:Sunlight; D013739:Testosterone / Q000097:blood*; D014807:Vitamin D / Q000097:blood
chemical_list: D014807:Vitamin D; D013739:Testosterone; D008550:Melatonin
keywords: Hypogonadism; Melatonin; Seasonal variation; Testosterone; Vitamin D