Endocrine responses to nocturnal eating--possible implications for night work.
BACKGROUND
Night work is becoming more common and shift workers display several metabolic disturbances. Aim To study the endocrine responses in relation to time of day during a 24-h period and how dietary macronutrient composition affects these responses.


METHODS
Seven males (26-43 y and 19.9-26.6 kg. m(-2)) were studied in a crossover design. Isocaloric diets described as high-carbohydrates (HC; 65 energy percent (E%) carbohydrates and 20E% fat) or high-fat (HF; 40E% carbohydrates and 45E% fat) were given. After a 6-day diet adjustment period, the subjects were kept awake for 24 h in a metabolic unit and were served an isocaloric meal (continuation of respective diet) every 4-h. Blood samples were taken throughout the 24-h period.


RESULTS
Insulin and leptin responses to meal intake differed with respect to time of day (p < 0.05). Time of day affected glucagon, thyroid stimulating hormone (TSH), free thyroxin (fT4), total triiodothyronine (tT3), cortisol, chromogranin A (CgA) and pancreatic polypeptide (PP) concentrations (p < 0.05). Meal intake decreased cortisol concentration after meals at 0800, 1200 and 0400 but not at 1600, 2000 and 0000 h. The PP's postprandial increase was greater during 0800-1600 h compared to 2000-0800 h. With the HC meals, lower glucagon and CgA concentrations (p < 0.05), and a tendency for lower tT3 concentrations (p = 0.053) were observed compared to the HF meals.


CONCLUSIONS
Insulin, PP, TSH, fT4, cortisol and leptin responses to meal intake differed with respect to time of day. The decreased evening/nocturnal responses of cortisol and PP to meal intake indicate that nocturnal eating and night work might have health implications.
Holmbäck
Ulf
U
Department of Medical Sciences, Clinical Chemistry, Uppsala University Hospital, 751 85 Uppsala, Sweden. ulf.holmback@medsci.uu.se
Forslund
Anders
A
Lowden
Arne
A
Forslund
Jeanette
J
Akerstedt
Torbjörn
T
Lennernäs
Maria
M
Hambraeus
Leif
L
Stridsberg
Mats
M
D000328:Adult; D000704:Analysis of Variance; D002940:Circadian Rhythm / Q000502:physiology*; D018592:Cross-Over Studies; D004040:Dietary Carbohydrates / Q000378:metabolism; D004041:Dietary Fats / Q000378:metabolism; D005247:Feeding Behavior / Q000502:physiology*; D006728:Hormones / Q000097:blood*; D006801:Humans; D008297:Male; D009490:Neurosecretory Systems / Q000502:physiology*; D013997:Time Factors; D014940:Work Schedule Tolerance / Q000502:physiology*
D004040:Dietary Carbohydrates; D004041:Dietary Fats; D006728:Hormones