It’s hardly a secret that constantly working the night shift can have all sorts of long-term consequences for your health, from an increased risk of heart disease and certain types of cancer to obesity. Less certain though is why and how that happens.

Now, a team of researchers from the Brigham and Women's Hospital (BWH) in Boston, MA claim that they’ve landed upon at least part of the answer, publishing their findings Monday in the Proceedings of the National Academy of Sciences. Studying a group of volunteers as they called the BWH sleep laboratory their temporary home for 16 days, the team closely looked at how the volunteers' bodies reacted when they rapidly inverted their normal sleep/wake and fasting/feeding cycles by a full 12 hours. This short-term disruption of their circadian rhythm, or circadian misalignment, in turn led to higher levels of risk factors known to promote cardiovascular disease, even after accounting for other factors like diet and family history.

"We were able to determine, under highly controlled laboratory conditions, the independent impact of circadian misalignment on cardiovascular disease risk factors — blood pressure and inflammatory markers," said senior author Dr. Frank Scheer, a neuroscientist in the Division of Sleep and Circadian Disorders at BWH, in a statement. "Our findings provide evidence for circadian misalignment as an underlying mechanism to explain why shift work is a risk factor for elevated blood pressure, hypertension, inflammation and cardiovascular disease."

The volunteers actually took part in two separate 8-day stays at the BWH sleep lab. For one stay, they slept as they normally would have, allowing the researchers to extensively keep track of their typical state of health. During the second, they again slept as usual for the first three nights, but from there, they switched to a 11 a.m. to 7 p.m bedtime — effectively mimicking the lifestyle of a night shift worker.

Compared to their normal health readings, the volunteers’ circadian misalignment was associated with higher blood pressure (both systolic and diastolic) for 24 hours afterward, less autonomic nervous system activity, and increased signs of inflammation. The typical lowering of blood pressure seen in sleep was also weakened when people slept during the day, indicating their bodies were less able to regulate blood pressure on the fly.

Though the study’s design enabled the authors to carefully tease out the health effects an misaligned body clock can have on certain people, the findings can’t definitively tell us how it affects people with already dysfunctional work schedules or preexisting health conditions.

"Our study evaluated ‘short-term’ circadian misalignment in healthy adults. The effect of circadian misalignments on cardiovascular function and inflammatory markers may be different in people with hypertension, and in shift workers," explained lead author Dr. Christopher J. Morris, associate physiologist in the Division of Sleep and Circadian Disorders at BWH.

Morris also noted that understanding how circadian misalignment wrecks havoc on the body is only part of the puzzle. "Further research is needed to investigate countermeasures for the adverse cardiovascular effects of circadian misalignment, such as the timing of eating and exercise."

Source: Morris C, Scheer F, et al. Proceedings of the National Academy of Sciences. 2016.