Sleeping just four hours a night for three days raises stress-related proteins in the blood that can harm the heart, new research has found.
Scientists found that three nights of restricted sleep led to a rise in inflammatory proteins – molecules the body produces when it is under stress or fighting illness.
Persistently high levels of these can damage blood vessels and increase the risk of conditions such as heart failure, coronary heart disease and atrial fibrillation, a type of irregular heartbeat.
The study involved 16 healthy young men who spent several days in a lab, where their meals, activity levels and light exposure were carefully controlled.
Participants followed two routines: three nights of normal sleep (8.5 hours) and three nights of restricted sleep (4.25 hours).
After each phase, the men completed a short, high-intensity cycling workout, with blood tests taken before and after.
Researchers measured almost 90 different proteins in the blood samples. They found that sleep deprivation caused a clear rise in inflammatory markers linked to heart disease.
While exercise typically boosts helpful proteins such as interleukin-6 and BDNF – which support brain and heart health – these responses were weaker after poor sleep.
The researchers from Uppsala University said the changes occurred even in healthy young adults and after only a few nights of restricted rest.
They also found that the timing of blood collection made a difference. Protein levels varied between morning and evening, with greater fluctuations when sleep was restricted.
This suggests that lack of sleep affects not only the presence of certain blood markers but also when these changes are most visible.
The findings come as poor sleep remains widespread – especially among shift workers, who make up about one in four adults.
Experts warn that while it may seem harmless to sacrifice rest for work, socialising or screen time, the body quietly keeps track through changes in its chemistry.
