Disrupted gene activity may be the reason jet lag kicks our butts so badly according to research from a British university. They found that both jet lag and working nightshifts affected the activity of more than 1,500 genes.

The Surrey University study looked at the levels of gene expression, in which a gene’s information is used to create either a protein or RNA, one of the most fundamental steps in the body’s operation.

The study involved 22 people staying in an indoor facility where the lighting cycle was set to simulate a 28-hour rather than 24-hour day. The subjects spent three (real) days in the facility, after which they were effectively 12 hours out of sync.

Reporting on the study, The Guardian noted that the researchers measured activity levels for 1,396 genes which normally vary throughout the day in a regular cycle. The rhythms of all but around 40 were disrupted at the end of the study.

Perhaps even more strikingly, the researchers also found that another 180 genes that normally have a constant activity level unaffected by the time of day had developed cycles over the test.

The report of the study, publishing in the Proceedings of the National Academy of Sciences, noted that although it’s possible the changing gene expression levels have negative health consequences, the study didn’t set out to prove such a link. It did note parallels to the aging process: as people get older, the variation of gene expression across the cycle becomes less pronounced.

The Guardian also explained that some drugs are designed to work at a particular time of day and that this could be disrupted by jetlag or keeping unusual time patterns. It also pointed out this could be a particular issue for patients in intensive care who aren’t exercising or eating to a regular schedule and may not be exposed to natural sunlight cycles.