Working night shifts as a teenager is not only exhausting; it also significantly increases the chance of developing multiple sclerosis later in life, according to a Swedish study.

“Our analysis revealed a significant association between working (night) shifts at a young age and occurrence of MS,” Anna Hedstroem, who headed the team of Karolinska Institute researchers, said in a statement.

For the study, published in the Annals of Neurology, the researchers combed through data from two Swedish population-based studies: One with all newly diagnosed MS cases since 2004, or 1,343 people and 2,900 control individuals without the disease, and another group of 5,129 people registered with pre-existing MS diagnoses and a 4,509-strong control group.

All of the study subjects were between 16 and 70 and were asked questions about their work life and whether they had ever worked odd hours.

The team compared the occurrence of MS among study subjects exposed to shift work – defined as working any time between the hours of 9 p.m. and 7 a.m. – at various ages against those who had never worked night shifts.

The result was astounding: in both groups the researchers found that those who had worked night shifts for longer periods of time before they turned 20 had twice the risk of developing MS compared to those who never worked shifts.

The researchers suggest that disrupting a person’s circadian rhythm, or daily rhythmic activity cycle, along with sleep loss could play a role in the development of MS.

“With shift work, your biological clock gets out of whack and you have poorer sleep quality (and) both these things have been shown to impact the immune system,” according to Dr Hedstroem.