People who get too much or too little sleep are more likely to show early signs of heart disease, a new study has found.

According to the findings, seven hours of good quality sleep appears to be the most beneficial for the heart.

Researchers in South Korea looked at more than 47,000 young and middle-aged adults. All completed detailed sleep questionnaires and underwent extensive heart tests.

The study found that adults who slept for less than five hours per day had 50% more calcium in their coronary arteries than those who slept for seven hours a day. Calcium in the coronary arteries is an early sign of heart disease.

Those who slept for nine hours or more a day had over 70% more calcium in their coronary arteries than those who slept for seven hours.

Meanwhile, those who said they had poor quality sleep had over 20% more calcium in their coronary arteries.

"We also observed a similar pattern when we measured arterial stiffness (another early sign of heart disease). Adults with poor sleep quality have stiffer arteries than those who sleep seven hours a day or had good sleep quality.

"Overall, we saw the lowest levels of vascular disease in adults sleeping seven hours a day and reporting good sleep quality," explained the study's co-lead author, Dr Yoosoo Chang, of the Center for Cohort Studies at Kangbuk Samsun Hospital.

The researchers highlighted the fact that ‘inadequate sleep is a common problem' and called on doctors to consider assessing their patients' quality of sleep when they are evaluating their heart health.

Details of these findings are published in the journal, Arteriosclerosis, Thrombosis and Vascular Biology.

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