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Introduction: The light/dark cycle of the environment is synchronized with the metabolism. However, in modern society, artificial light is available 24/7, and many people are often exposed to bright light during periods that should be darker. This illumination pattern has a negative effect on metabolism. This study shows that indoor lighting conditions close to the natural light/dark cycle can help improve blood sugar control and increase postprandial energy expenditure.
Recently, maastricht University Medical Center in the Netherlands conducted a study to compare the metabolic response of individuals at risk of metabolic diseases under natural light/dark cycles and suboptimal lighting conditions. The study was published in the journal Diabetlogia.
Research design
The researchers conducted a randomized controlled crossover trial of 14 overweight adults between the ages of 40 and 75 who met one of the four criteria for insulin resistance. Also, participants who slept around 11 p.m. and slept for 7 to 9 hours were included. Participants stay in the metabolic room for two 40 hours each starting at 6 p.m. on day 1 and ending at noon on day 3.
➤ In the first session (simulating the laws of nature), participants were in bright light from 8 am to 6 pm and in dim light from 6 pm to 11 pm.
➤ The second phase (contrary to the laws of nature), with an interval of at least 4 days, participants were in dim light from 8 am to 6 pm and bright lights from 6 pm to 11 pm.
Subjects wore an activity recorder to measure sleep patterns before and during the trial. Energy expenditure, sleep metabolic rate, and matrix oxidation are calculated based on oxygen consumption and carbon dioxide production. A wireless sensor is used to measure the skin temperature. Fasting blood samples were taken at 7:45 a.m. on Day 2 and 3 at 5:45 p.m. on Day 2, respectively, and postprandial blood samples were taken every 30 hours after breakfast and every 30 minutes after dinner on Day 2 (Figure 1).
Figure 1 Study protocol
Bright daytime lighting lowers blood sugar
Participants in the second phase had greater elevations in triglycerides (P=0.029) after breakfast the next day than participants in the first phase (Figure 2 d). Participants in the first phase had lower blood glucose (5 mmol/L vs.5.2 mmol/L; P=0.02) than participants in the second phase (Figure 2b).
Fig. 2 Plasma changes after a meal
Bright daytime lighting improves energy consumption
Energy expenditure: The energy expenditure of the second and third days does not differ significantly in different lighting modes. In the post-dinner phase of breakfast the next day, there was no difference in energy expenditure. After dinner, participants in the first phase had more postprandial energy expenditure than participants in the second phase. (Figure 3a)
Sleep metabolic rate (SMR): The nighttime SMR of the phase II participants was lower than that of the phase I participants (Figure 3b). The respiratory exchange ratio did not differ under different conditions at any time interval.
Figure 3 Energy Consumption and SMR
conclusion
Bright daytime-dim night conditions mostly yield favorable results compared to dim day-bright night conditions: lower preprandial blood glucose levels and more postprandial energy expenditure.
Author: Rain Text
Review: Tian Zi Ge
bibliography:
[1] Harmsen JF, Wefers J, Doligkeit D. et al. The influence of bright and dim light on substrate metabolism, energy expenditure and thermoregulation in insulin-resistant individuals depends on time of day. Diabetologia (2022).