BALTIMORE—Night work may impair glucose tolerance, which is associated with lower postprandial, early-phase insulin levels, according to research presented at the 27th Annual Meeting of the Associated Professional Sleep Societies.
“These findings support a causal role of night work in the increased type 2 diabetes risk among shift workers,” reported Christopher Morris, PhD, a postdoctoral research fellow at the Division of Sleep Medicine, Brigham & Women’s Hospital, and at the Harvard Medical School in Boston.
Dr. Morris and colleagues evaluated 13 healthy, nonobese adults (eight men; age range, 20 to 49) without a significant history of shift work. All subjects completed two, eight-day, in-laboratory protocols in random order—one that included day work and the other simulated night work, in which the sleep/wake and fasting/feeding cycles were inverted by 12 hours. Each condition included four baseline days, followed by either day or night shifts.
Participants were on an isocaloric diet, which was identical between conditions. The diet included standardized mixed meals on days one and three of day and night work to allow for assessment of serum glucose and insulin responses. Subjects began eating the meal at 8 am (day work) or 8 pm (night work) and had to finish eating within 20 minutes. A blood sample was taken before the meal, and then every 10 minutes for 90 minutes, followed by every 30 minutes for 90 minutes.
The researchers reported results relating to mixed meal consumption on day one of day and night work. Fasting glucose levels were similar for day and night work (85 mg/dL). However, during night work, peak glucose levels were 16% higher compared with during day work (193 vs 166 mg/dL, respectively). “There was a significant interaction of time since meal, with slower decline of glucose levels during night work,” stated the investigators.
Fasting insulin levels were 15% lower during night work than during day work (4.3 vs 5.1 uIU/mL, respectively), and peak insulin levels were 13% lower during night work compared with at day work (86 vs 99 uIU/mL, respectively).
The researchers also observed a significant interaction of time since meal for insulin. During night work, subjects had 33% to 41% lower insulin levels at minutes 20 and 30, but the levels were 40% to 50% higher at minutes 80 and 90, possibly due to higher glucose values during night work, according to the study authors.
“It is surprising that just a single night shift can significantly impair glucose tolerance and increase insulin levels,” said Dr. Morris. “These findings are important, because they demonstrate, under highly controlled lab conditions, that acute exposure to night work impairs glucose tolerance. Chronic, impaired glucose tolerance is likely to lead to type 2 diabetes.”
—Colby Stong
Editor
Suggested Reading
Axelsson J, Puttonen S. Night shift work increases the risk for type 2 diabetes. Evid Based Med. 2012;17(6):193-194.
Pan A, Schernhammer ES, Sun Q, Hu FB. Rotating night shift work and risk of type 2 diabetes: two prospective cohort studies in women. PLoS Med