Meta-Analysis Links Night Shift to Obesity Risk, Especially "Belly Fat"

Days after the Nobel Prize went to scientists who discovered the genes that control our body clock, a review of 28 studies shows what happens when you fight Mother Nature: the meta-analysis shows working the night shift increases the risk of obesity, which means nurses, police officers, firefighters, and warehouse staff need to take precautions to avoid abdominal obesity.

“Shift work has recently been identified as an important occupational hazard, with a growing body of evidence showing an association between shift work and adverse health effects such as metabolism abnormalities that include obesity,” authors from the Chinese University of Hong Kong, write in their paper, which appears online today in Obesity Reviews.

The study found the following:

• Overall, the risk of being overweight or obese from working the night shift is 23% higher.
• Shift workers had a 35% higher risk of developing abdominal obesity than other obesity types; abdominal obesity, or “belly fat,” is especially associated with heart disease.
• The analysis found that those who worked the night shift permanently were at 29% greater risk of abdominal obesity than those who worked rotating shifts.
• While modification of work schedules is the most obvious remedy, this may be a challenge, since shift work is increasing.

“Globally, nearly 700 million workers are engaged in a shift work pattern. Our study revealed that much of the obesity and overweight among shift workers is attributable to such a job nature,” said the study’s senior author, Lap Ah Tse, PhD, in a statement.

“Obesity has been evident to be positively associated with several adverse health outcomes, such as breast cancer, and cardiovascular diseases,” she said. Heart disease is the number one killer in the United States, followed by cancer. Diabetes, which is also strongly associated with obesity, is the seventh-leading cause of death.

Researchers who have conducted laboratory experiments involving study subjects who sleep during the day and are awake at night find that the reversal of circadian rhythm causes the metabolism to slow and the body to produce less insulin, giving it less ability to control blood glucose. While the effect may be slow, it translates into higher weight over time. Practically speaking, night shift workers may have less access to healthy food choices.

Reference

Sun M, Feng W, Wang F, et al. Meta-analysis on shift work and risks of specific obesity types [published online October 4, 2017]. Obes Rev. doi: 10.1111/obr.12621.