Recent changes in how shift work is scheduled may help reduce the health risks faced by people who worked certain shifts in the past, a new study suggests.

"Recent research has suggested shift work could increase the risk of cancer, although the biological mechanism responsible for this observation is still unknown," the study's lead author, Anne Grundy, a doctoral student in the Queen's University department of community health and epidemiology in Ontario, said in a university news release. "Our study indicates that the now common rotating shift pattern of day-day-night-night may not disrupt circadian rhythm or melatonin production significantly."

The researchers studied 123 Kingston General Hospital shift workers who wore light-intensity meters to monitor their melatonin levels. Melatonin, a hormone with anti-carcinogenic qualities, linked to the light-dark cycle. Melatonin levels typically peak between midnight and 4 a.m., which could increase the cancer risk for shift workers who are exposed to light throughout the night.

However, the study determined that recent changes in how shifts are scheduled may help reduce the health risks for these workers. A reduction in the nighttime lighting intensity at Kingston General Hospital, where the study took place, lead to peak melatonin levels in night-shift workers that were similar to those who worked during the day. In cases where the night workers were exposed to more light, however, the workers' overall change in melatonin levels decreased slightly -- a statistically significant finding, according to the the study's authors.

"We've already seen a shift away from the older patterns of two weeks of days, two weeks of nights and a short time off, to more humane patterns of day-day-night-night then five days off, so it's possible that an intervention to combat the health risks of shift work has already occurred."

"However, the overall change in melatonin levels that we found may still be a concern," she added. "We look forward to seeing other studies that either confirm our findings or that examine the impact of specific risk factors like extreme shift patterns and higher intensities of light at night."

The study was published online in Cancer Epidemiology, Biomarkers & Prevention.