The role of eating behavior in reducing the risk of type 2 diabetes among nighttime shift workers

Does daytime eating prevent glucose intolerance and internal circadian misalignment in night shift workers?

Several studies have suggested that rotating night shift work ((defined as working at least three nights/month in addition to 19 days and evenings in that month) is associated with an increased risk of obesity and metabolic syndrome, both of which are related to type 2 diabetes (T2D). In addition, previous work on animal models suggested that “mixed messages” received by metabolic organs result from synchronization conflict between central circadian pacemaker and fasting/eating cycle and can disrupt metabolic processes.

The association between rotating night shift and T2D was primarily based on data obtained from Nurses’ Health Study I (NHS I) established in 1976. It included 121,704 women, and the Nurses’ Health Study II (NHS II) was established in 1989 and included 116,677 women without diabetes, cardiovascular disease, and cancer at baseline. All participants were asked to report how long they had worked rotating night shifts. The incidence of T2D was confirmed by a validated supplementary over 18-20 years. The study showed a significantly increased risk of T2D in women who reported extended periods of rotating night shifts.

A recent study by Chellappa et al., on the other hand, explored the mechanisms underlying the effects of meal timing on circadian misalignment among nightshift workers on impaired glucose tolerance. 19 health volunteers [12 men, 7 women, age 26.5 ± 4.1 years; body mass index (BMI), 22.7 ± 2.1 kg/m2; hemoglobin A1c (HbA1c) range, 4.9 to 5.4%] were subjected to a 14-day controlled circadian laboratory protocol. First, a baseline routine simulating day work was established under stable behavioral and environmental conditions. The subjects were then subjected to a forced desynchrony to simulate night work, and participants were out of sync by the end of day 4. Participants were subsequently divided into two groups, the Nighttime meal control (NMC) group (n = 10), with the participants consuming meals during both the daytime and nighttime and the daytime intervention (DMI) group (n = 9) where meal consumption occurred only during the daytime. All participants had a 40-hour post-misalignment constant routine (CR) to evaluate the effects of simulated night work on central circadian rhythms (cire body temperature) and peripheral endogenous circadian rhythms (by a sampling of hourly levels of blood glucose and insulin).

The results obtained from the meal timing intervention after simulated night work in both the Nighttime meal control (NMC) group or the Daytime meal intervention (DMI) group did not show a significant effect on the endogenous circadian core body temperature (CBT) Rhythms, resting energy expenditure, endogenous circadian insulin rhythms. Meal timing intervention showed a significant impact on the endogenous circadian glucose rhythm, however (pFDR = 0.001), and the 3-hour postprandial glucose significantly increased by 19.4% [95% CI, 4.7 to 34.2% (18.4 mg/dl; 95% CI, 4.8 to 31.8 mg/dl). No significant changes were observed relative to baseline in the DMI group [95% CI, −13.9 to 10.1% (−15.6 to 12.8 mg/dl). Additionally, no significant impact of simulated night work on the 3-hour postprandial 3-hour glucose profile or insulin relative to baseline was observed after the dinner test meal [95% CI, −8.5 to 0.4% (−6 to 0.1 μU/ml)]. However, postprandial early-phase insulin was significantly modified after the breakfast test meal (pFDR = 0.008). In the NMC group, simulated night work, there was a decrease of postprandial early-phase insulin after the breakfast test meal of −52.9% [95% CI, −98.6 to −7.1% (−23.5 μU/ml; 95% CI, −42.8 to −4.2 μU/ml); but not in the DMI group [95% CI, −39.8 to 3.4% (−24.1 to 1.3 μU/ml).

The study concluded that daytime meal intervention in humans could lead to internal circadian alignment during the feed-fast cycle controlled by the central circadian pacemaker and is independent of exposure to circadian misalignment of the sleep/wake cycle. Loss of balance between the fasting/eating cycle and the central circadian pacemaker may explain the increased metabolic risk among shift workers and underline the significance of meal timing to mitigate the effect of the internal circadian misalignment on glucose intolerance among shift workers.

Practice Pearls:

• There is a positive association between the degree of internal circadian misalignment and impaired glucose tolerance during simulated night work.
• Daytime meal intake by nighttime shift workers is associated with internal circadian alignment and, hence, better glucose tolerance and pancreatic β cell function.
• Endogenous circadian glucose rhythms remained under baseline even during simulated night work conditions when food was restricted to the daytime.

References:

Chellappa, Sarah L., et al. “Daytime Eating Prevents Internal Circadian Misalignment and Glucose Intolerance in Night Work.” Science Advances, vol. 7, no. 49, 2021, https://doi.org/10.1126/sciadv.abg9910. 

Pan, An et al. “Rotating night shift work and risk of type 2 diabetes: two prospective cohort studies in women.” PLoS medicine vol. 8,12 (2011): e1001141. doi:10.1371/journal.pmed.1001141

Elmoataz Elmamoun

PharmD Candidate, 2022, South College School of Pharmacy