Scientists say that working at night might make you fat and unsociable working hours slow the body's natural metabolism.
After closely monitoring people with disrupted sleep patterns, researchers discovered that working at night and sleeping during the day affects the body's natural rhythms and slows down the rate it burns energy.
According to Harvard Medical School scientists, the result, known as circadian misalignment, could lead to increased risks from obesity, diabetes and even heart disease.
Circadian misalignment refers to the body's own natural biological clock which regulates when we want to sleep, eat and wake, reports The Telegraph.
To reach the conclusion, researchers took 10 volunteers and subjected them in a laboratory to the equivalent of working various shift patterns during a 10-day period.
The volunteers were monitored for alterations in heart rate and body temperature which all implied a slowing of the metabolic rate.
They also showed changes to levels in certain hormones important to feelings of stress and well-being.
The disrupted patterns also caused three patients with no diabetes history to exhibit signs similar to people who are more susceptible to developing the condition.
After analysing, the researchers conclude that the combination of these effects may help explain the increased risk of obesity, high blood pressure and diabetes found in shift workers.