IT’S widely thought that eight hours is the magic number when it comes to getting enough sleep.
But now scientists have found that you could lower your risk of heart disease with fewer hours in bed.
People whose kip was restricted to five hours had higher blood pressure and heart rates — even if they made up for it on the weekend, US researchers found.
You should aim to sleep above that amount every day to help avoid the deadly condition in the long-term, they suggested.
Dr Anne-Marie Chang, of Penn State University, said: “There’s a lot of evidence suggesting that this lack of sleep is associated with cardiovascular disease in the long term.
“Our research reveals a potential mechanism for this relationship.
“Enough successive hits to your cardiovascular health while you’re young could make your heart more prone to cardiovascular disease in the future.”
Around 7.6million Brits live with a heart or circulatory disease, according to the British Heart Foundation.
High blood pressure can increase your risk of heart disease because it damages your arteries by making them less elastic, decreasing the flow of blood and oxygen to your heart.
The NHS recommends adults get seven to nine hours sleep, while children need nine to 13.
Previous research has shown your blood pressure falls while you’re asleep — and missing out on sleep keeps it higher for longer.
The latest study, published in Psychosomatic Medicine, looked at how this builds up over successive days, as well as the effects of sleep on heart rate.
Researchers took blood pressure and heart rate measurements from 15 healthy men aged 20 to 35 every two hours for 11 days.
For the first three nights, they were allowed to sleep for 10 hours to return to baseline sleep levels.
They were then restricted to five hours per night for five nights, followed by two recovery nights, when they were allowed to sleep 10 hours again.
Heart rate increased nearly one beat per minute with each successive day on average.
The average baseline heart rate was 69 BPM, while the average heart rate by the end of the study on the second day of recovery was nearly 78 BPM.
Systolic blood pressure also increased by about 0.5 millimeters of mercury per day.
The average baseline systolic blood pressure was 116 mmHg and was nearly 119.5 mmHg by the end of the recovery period.
Lead author David Reichenberger said: “Both heart rate and systolic blood pressure increased with each successive day and did not return to baseline levels by the end of the recovery period.
“So, despite having additional opportunity to rest, by the end of the weekend of the study, their cardiovascular systems still had not recovered.”