The researchers studied 683 Caucasian men, comparing 437-day workers to 246 rotating shift workers. Day and night work periods began at 6 a.m. and 6 p.m.
The research, which is published in the journal Sleep, and led by Carlos Pirola, notes that all subjects stuck to the same schedule throughout the study.
As part of the study, serotonin levels of the shift workers were measured through blood tests. It was seen that these levels were much lower than the levels of workers on regular day schedules.
Shift workers were also found to have greater hip-to-waist ratios, higher cholesterol and insulin levels, increased blood pressure and higher triglyceride levels.
According to scientists, low levels of serotonin are associated with conditions such as anger, depression and anxiety.
Previous studies have found rotating and nightshift work affect the cardiovascular and metabolic systems. These also suggest that shift work may be directly responsible for increased body fat and higher blood pressure levels, say the authors.
As serotonin governs sleep patterns, among other body functions, the authors believe that shift work also leads to so-called shift work sleep disorder. People with the disorder tend to remain awake when they should be sleeping. But during waking hours, they may be severely tired.
Shift workers in the study typically slept one to four hours less than average, and experienced a poor quality of sleep.
Sound sleep is invaluable as lack of high-quality sleep can sabotage job performance, make people less alert and put them at risk of an injury on the job, the researchers said.