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The effects of season, daylight saving and time of sunrise on serum cortisol in a large population.
Chronobiol Int. 2014 Mar; 31(2):243-51.CI

Abstract

Cortisol is critical for maintenance of health and homeostasis and factors affecting cortisol levels are of clinical importance. There is conflicting information about the effects of season on morning cortisol and little information on the effects of sunlight on population cortisol assessment. The aim of this study was to assess whether changes in median serum cortisol occurred in a population in conjunction with changing seasons, daylight saving time (DST) or time of sunrise. We analysed serum cortisol results (n = 27,569) from a single large laboratory over a 13-year period. Subjects with confounding medications or medical conditions were excluded and data analysed in 15-minute intervals. We assessed the influence of traditional seasons, seasons determined by equinox/solstice, DST and time of sunrise on median cortisol. The median time of cortisol collection did not vary significantly between seasons. Using traditional seasons, median cortisol was lowest in summer (386 nmol/L) and spring (384 nmol/L) with higher cortisol in autumn (406 nmol/L) and winter (414 nmol/L). Median cortisol was lowest in the summer solstice quarter with significant comparative increases in the spring equinox quarter (3.1%), the autumn equinox quarter (4.5%) and the winter solstice quarter (8.6%). When cortisol was modelled against time, with adjustment for actual sunrise time on day of collection, for each hour delay in sunrise there was a 4.8% increase in median cortisol (95% CI: 3.9-5.7%). In modelling to explain the variation in cortisol over the morning, sunrise time was better than season in explaining seasonal effects. A subtle cyclic pattern in median cortisol also occurred throughout the months of the year. A 3-year trial of DST allowed comparison of cortisol in DST and non DST periods, when clock time differed by one hour. There was modest evidence of a difference in acrophase between DST and non DST cortisol (p = 0.038), with DST peak cortisol estimated to occur 58 minutes later than non-DST peak. In summary, we found that time of sunrise and time of cortisol collection were the most important factors influencing median cortisol. For each hour later that the sun rose there was an almost 5% increase in median cortisol. There was significant seasonal variability with lowest cortisol noted in summer coinciding with the earliest sunrise time. This is an important finding which is consistent with the understanding that light is the major zeitgeber in entrainment of the human circadian cortisol rhythm. Our data suggest this rhythm is resistant to the arbitrary changes in clock time with daylight saving.

Authors+Show Affiliations

Department of Clinical Biochemistry, PathWest Laboratory Medicine, Queen Elizabeth II Medical Centre , Nedlands, Western Australia , Australia .No affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Comparative Study
Journal Article

Language

eng

PubMed ID

24156521

Citation

Hadlow, Narelle C., et al. "The Effects of Season, Daylight Saving and Time of Sunrise On Serum Cortisol in a Large Population." Chronobiology International, vol. 31, no. 2, 2014, pp. 243-51.
Hadlow NC, Brown S, Wardrop R, et al. The effects of season, daylight saving and time of sunrise on serum cortisol in a large population. Chronobiol Int. 2014;31(2):243-51.
Hadlow, N. C., Brown, S., Wardrop, R., & Henley, D. (2014). The effects of season, daylight saving and time of sunrise on serum cortisol in a large population. Chronobiology International, 31(2), 243-51. https://doi.org/10.3109/07420528.2013.844162
Hadlow NC, et al. The Effects of Season, Daylight Saving and Time of Sunrise On Serum Cortisol in a Large Population. Chronobiol Int. 2014;31(2):243-51. PubMed PMID: 24156521.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - The effects of season, daylight saving and time of sunrise on serum cortisol in a large population. AU - Hadlow,Narelle C, AU - Brown,Suzanne, AU - Wardrop,Robert, AU - Henley,David, Y1 - 2013/10/24/ PY - 2013/10/26/entrez PY - 2013/10/26/pubmed PY - 2015/2/13/medline SP - 243 EP - 51 JF - Chronobiology international JO - Chronobiol Int VL - 31 IS - 2 N2 - Cortisol is critical for maintenance of health and homeostasis and factors affecting cortisol levels are of clinical importance. There is conflicting information about the effects of season on morning cortisol and little information on the effects of sunlight on population cortisol assessment. The aim of this study was to assess whether changes in median serum cortisol occurred in a population in conjunction with changing seasons, daylight saving time (DST) or time of sunrise. We analysed serum cortisol results (n = 27,569) from a single large laboratory over a 13-year period. Subjects with confounding medications or medical conditions were excluded and data analysed in 15-minute intervals. We assessed the influence of traditional seasons, seasons determined by equinox/solstice, DST and time of sunrise on median cortisol. The median time of cortisol collection did not vary significantly between seasons. Using traditional seasons, median cortisol was lowest in summer (386 nmol/L) and spring (384 nmol/L) with higher cortisol in autumn (406 nmol/L) and winter (414 nmol/L). Median cortisol was lowest in the summer solstice quarter with significant comparative increases in the spring equinox quarter (3.1%), the autumn equinox quarter (4.5%) and the winter solstice quarter (8.6%). When cortisol was modelled against time, with adjustment for actual sunrise time on day of collection, for each hour delay in sunrise there was a 4.8% increase in median cortisol (95% CI: 3.9-5.7%). In modelling to explain the variation in cortisol over the morning, sunrise time was better than season in explaining seasonal effects. A subtle cyclic pattern in median cortisol also occurred throughout the months of the year. A 3-year trial of DST allowed comparison of cortisol in DST and non DST periods, when clock time differed by one hour. There was modest evidence of a difference in acrophase between DST and non DST cortisol (p = 0.038), with DST peak cortisol estimated to occur 58 minutes later than non-DST peak. In summary, we found that time of sunrise and time of cortisol collection were the most important factors influencing median cortisol. For each hour later that the sun rose there was an almost 5% increase in median cortisol. There was significant seasonal variability with lowest cortisol noted in summer coinciding with the earliest sunrise time. This is an important finding which is consistent with the understanding that light is the major zeitgeber in entrainment of the human circadian cortisol rhythm. Our data suggest this rhythm is resistant to the arbitrary changes in clock time with daylight saving. SN - 1525-6073 UR - https://www.unboundmedicine.com/medline/citation/24156521/The_effects_of_season_daylight_saving_and_time_of_sunrise_on_serum_cortisol_in_a_large_population_ L2 - https://www.tandfonline.com/doi/full/10.3109/07420528.2013.844162 DB - PRIME DP - Unbound Medicine ER -