In a new study from Uppsala University in Sweden, scientists found that just three nights of restricted sleep - about four hours a night - caused changes in the blood that are linked to a higher risk of heart disease. The researchers studied inflammatory proteins in the blood.

The results of the study are published in the journal BMC.

 These are molecules that the body produces when it is stressed or fighting disease. When levels of these proteins remain high for a long time, they can damage blood vessels and increase the risk of problems such as heart failure, coronary heart disease and atrial fibrillation (irregular heartbeat).

The study involved 16 healthy young men who spent several days in a laboratory where everything from food intake to physical activity levels and light levels were carefully monitored. The participants followed two regimens: three nights of regular sleep (8.5 hours) and three nights of restricted sleep (4.25 hours).

After each sleep phase, the men performed a short, high-intensity bike workout, and their blood was analyzed before and after. The researchers measured the content of nearly 90 different proteins in the blood samples. They found that lack of sleep caused a clear increase in inflammatory markers associated with heart disease. And while exercise typically increases levels of beneficial proteins such as interleukin-6 and BDNF (which keep the brain and heart healthy), these responses weakened after poor sleep.  Strikingly, the changes occurred even in young, healthy people, and after just a few nights of poor sleep.