Shift work is linked to an increased risk of developing Type 2 diabetes, according to new research from China. An estimated 25.8 million people in the United States and 108 million people in China now have Type 2, with a predicted total of 380 million people expected to have the condition worldwide by 2025.
Previous research has linked shift work to a variety of health problems, including cardiovascular disease, digestive disorders, and certain cancers, as well as to both reduced glucose tolerance and an increased risk of Type 2 diabetes in women. The results regarding diabetes, however, have been inconsistent.
To further evaluate the relationship between shift work and Type 2, investigators from the Huazhong University of Science and Technology and the Jiangxi Science and Technology Normal University conducted a meta-analysis (analysis of data from several clinical trials) of 12 international studies involving 226,500 people, 14,600 of whom had diabetes.
Pooling the results from all of the studies, the researchers found that any period of shift work was linked with a 9% increase in Type 2 diabetes risk compared to working normal office hours. According to Robert Glatter, MD, of Lenox Hill Hospital, one likely explanation for the increased risk is the disruption of typical eating and sleeping patterns. Eating late at night, he suggests, may increase the likelihood of the calories being stored as fat, upping a person’s chances of obesity and, therefore, Type 2 diabetes.
Further analysis to look at the effects of variables such as gender, study design, study location, job, shift schedule, body-mass index (a measure of weight relative to height), family history of diabetes, and physical activity levels found that the risk rose to 37% for men. Although the researchers could not explain this heightened risk in men, they note that repeated disruption of the body clock may interfere with the male hormone testosterone, low levels of which have been implicated in insulin resistance and diabetes.
However, other factors may also be at play. In an interview with Forbes, Alan Manevitz, MD, a clinical psychiatrist at Lenox Hill Hospital, notes that “[The] study authors implicate the disruption of the male hormone testosterone as one potential trigger of insulin resistance and diabetes in study participants, but a wide array of other body chemicals are also skewed when normal sleep patterns are disrupted, including leptin and growth hormone.”
The highest risk from shift work was discovered in men and women with rotating shifts (in which work hours switch between varying portions of the 24-hour cycle), who were found to have a 42% increased risk of developing Type 2 diabetes. Rotating shifts, the researchers suggest, may make it more difficult to adjust to a regular sleep-wake cycle, potentially impacting the quality or quantity of sleep and leading to insulin resistance.
Although the study was large, the investigators note that it was observational and therefore cannot establish direct cause and effect.
For more information, read the article “Shift work associated with increased risk of type 2 diabetes” or see the study’s abstract in the journal Occupational & Environmental Medicine. And to learn more about possible causes of Type 2 diabetes, read “Type 2 Diabetes: Are We Closer to Knowing ‘Why?’” by Wayne Clark.