Shift work – and the various light exposures that go with it – can place some people at a greater risk of weight gain and obesity. But the impact of various light exposures inherent in shift work appear to affect the metabolism of each person differently, reported Edward L. Melanson, PhD, and his coinvestigators.

“Such individual differences were not explained by sex, age, weight, fat mass, or fat free mass,” Dr. Melanson and his coinvestigators wrote. “Thus, understanding mechanisms underlying such individual differences in waking and sleep energy metabolism and how they may or may not contribute to health outcomes … requires additional research.”

The investigators’ conclusions are based on the results of two studies. Both studies used whole-room, indirect calorimetry to measure energy expenditure. The participants, all of whom were free of medications and illicit drugs, maintained a consistent 8-hour sleep schedule before the study took place, and consumed a specified diet throughout the study. Meal tests were used to assess the participants’ glucose metabolism responses, a protocol cited as one of the study’s limitations.

The first study, comprising 15 healthy young adults, looked for changes in energy expenditure and glucose metabolism in response to different lighting conditions, such as full-spectrum bright light or blue-enriched bright light. In that study, no effects were found on patients’ metabolism. The other study, comprising 14 healthy young adults, used a simulated shift work protocol and found a decrease in 24-hour energy expenditure in certain individuals in response to circadian misalignment. “This finding may help identify individuals who may be at a higher risk of unwanted weight gain and obesity during shift work,” the investigators wrote.

Read the full report in Neurobiology of Sleep and Circadian Rhythms.

SOURCE: Melanson EL et al. Neurobiol Sleep Circadian Rhythms. 2017 Dec 29. doi: 10.1016/j.nbscr.2017.12.002 .