Getting the right mix of indoor lighting throughout the day — with bright lighting during most of the daytime, and dim lighting in the evening — may increase the overall amount of energy used by the body and promote relaxation at night, according to a new study published in the journal Diabetologia.
Scientists have long known that sleep quality is linked to various measures of diabetes risk and blood glucose control. Studies have found that a short sleep duration is linked to a higher risk of developing type 2 diabetes, and that sleeping better is linked to a lower risk for both type 2 and other health problems like high blood pressure. In people who already have diabetes, sleep quality is linked to blood glucose levels after meals, and in the long term, sleep disturbances are associated with a higher risk of dying. At the same time, treating sleep disorders is linked to improved outcomes in type 2 diabetes, so much that sleep quality may be considered an essential element of diabetes management.
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The latest study didn’t look at sleep quality, but instead at a related factor in the daily sleep-wake cycle — how much light you’re exposed to throughout the day. The study authors noted that in modern society, artificial light is available at nearly all times — with potentially damaging effects on the body’s natural light-based biological mechanisms, which regulate hormones related to sleep as well as other functions like energy expenditure (calories burned) and blood glucose levels. Most people, the researchers noted, expose themselves to artificial lighting after dark, which may damage sleep quality and other biological functions.
The goal of the study, the researchers wrote, was to compare certain biological responses to an optimal lighting cycle — bright during most of the day, but dim in the evening — versus a suboptimal lighting cycle that was too dim during the day or too bright after dark. The study’s participants were 14 overweight adults with insulin resistance, who each completed two different 40-hour laboratory-based study sessions. During one cycle, participants experienced an optimal 24-hour lighting protocol with bright light from 8:00 am until 6:00 pm, then dim light until 11:00 pm. During the other cycle, they experienced a mismatched 24-hour lighting protocol with dim light during the day and bright light in the evening. During both periods, participants had their energy expenditure and body temperature measured, and had blood samples taken frequently.
Optimal lighting linked to more calories burned, improved melatonin levels
The researchers found that during the optimal lighting cycle, participants had lower blood glucose levels before their evening meal at 6:00 pm, but had lower blood glucose levels after this meal during the mismatched lighting cycle. Compared with a “baseline” night that preceded the 24-hour cycle with regulated lighting, the optimal lighting cycle resulted in no change in energy expenditure, while the mismatched lighting cycle resulted in fewer calories being burned during sleep. The mismatched lighting cycle also resulted in less melatonin being produced in the evening — a natural hormone that helps the body relax and get ready to sleep. Taken together, these results suggest that inadequate light exposure during the day — or too much light exposure at night — could contribute to weight gain and poor sleep quality.
The researchers noted that this was a very small study with a short duration, but that the results justify further studies to look at how lighting affects energy expenditure, blood glucose levels, and sleep quality in more people over longer periods of time.
Want to learn more about sleeping well with diabetes? Read “Getting the Sleep You Need,” “Eating for Better Sleep” and “Quality of Sleep: A Tool for Diabetes Management.”
