Just three nights of poor sleep might harm your heart – new study

We’ve long known that a lack of sleep is bad for the heart – but scientists are now starting to understand exactly how it causes harm.

In a new study from Uppsala University in Sweden, researchers found that just three nights of restricted sleep – around four hours a night – triggered changes in the blood linked to a higher risk of heart disease.

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The researchers looked at inflammatory proteins in the blood. These are molecules the body produces when it is under stress or fighting off illness. When these proteins stay high for a long time, they can damage blood vessels and raise the risk of problems like heart failure, coronary heart disease and atrial fibrillation (irregular heartbeat).

The study involved 16 healthy young men who spent several days in a lab, where everything from their meals to their activity levels and light exposure was carefully controlled.

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The participants followed two routines: three nights of normal sleep (8.5 hours) and three night of sleep restriction (4.25 hours). After each sleep phase, the men completed a short, high-intensity cycling workout, and their blood was tested 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. And while exercise usually boosts healthy proteins such as interleukin-6 and BDNF (which support brain and heart health), these responses were weaker after poor sleep.

Even young adults

Strikingly, the changes happened even in young, healthy adults, and after only a few nights of bad sleep. That’s worrying given how common it is for adults to experience poor sleep from time to time – and around one in four people work shifts that disrupt sleep patterns.

The researchers also discovered that the time of day blood was taken mattered: protein levels varied between morning and evening, and even more so when sleep was restricted. This suggests that sleep affects not only what’s in your blood, but when those changes are most visible.

Although modern life often encourages us to trade sleep for productivity, socialising or screen time, studies like this remind us that the body keeps score – quietly, chemically and without compromise.