Work the night shift? You may be at higher risk of obesity, study says

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New research published in the journal "Obesity Reviews" last week suggests night shift workers have a higher risk of obesity or of being overweight.

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The research includes a meta-analysis of 28 observational studies that reported on an association between shift work and obesity, body mass index (BMI) or weight change.

Studies also had to meet a variety of criteria, including reliable assessment of shift work, conclusions with 95 percent confidence intervals and observational study designs.

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Here’s what the researchers found:

  • Night shift work increases risk of obesity/overweight by 23 percent.
  • Night shift work increases risk of abdominal obesity, which is characterized by visceral fat accumulation in the abdomen and is commonly associated with abnormal metabolic profiles (like insulin resistance), by 35 percent.
  • Night shift workers between midnight and 5 a.m. showed a pooled estimate odds ratio of 1:32, meaning the odds of obesity/overweight is 1.32 higher for night shift workers compared to non-night shift workers.
  • Permanent night shift work showed a higher risk of obesity/overweight than rotating shifts, possibly due to daytime environmental hours interrupting proper sleep.
  • Highest risks were among 10-hour permanent night shifts or 12-hour rotating shifts compared with other night shift work.

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Why are night workers at risk?

Night workers are often exposed to light at night, which disrupts their circadian rhythm and suppresses the creation of melatonin.

According to the study authors, melatonin plays a big role in regulating hormones, such as insulin, cortisol and leptin.

Suppressing the melatonin can in turn lead to abnormal metabolic profiles, which, as previously mentioned, is associated with abdominal obesity.

Sleep deprivation is also a major mechanism that alters metabolic profiles and increases body weight, authors noted.

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Study limitations

Though the cross-sectional meta-analysis has merits, there are some limitations. For example, the review had a high degree of heterogeneity, meaning the populations spanned a multitude of demographics, had varied smoking and drinking habits and more.

Another study limitation is the lack of definition for night shift work — multiple studies used vague vocabulary.

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Researchers suggest future studies should focus on large-scale prospective cohort studies, because cross-sectional research such as this one cannot determine cause and effect.

The authors also call on administrators to modify working schedules to avoid prolonged exposure to long-term night shift work.

Read the full study and its methodology, limitations and conclusions at onlinelibrary.wiley.com.