People suffering from insomnia may have an increased risk of heart attack and stroke, new research has warned.

"Sleep is important for biological recovery and takes around a third of our lifetime, but in modern society more and more people complain of insomnia," said Qiao He from China Medical University.

"Researchers have found associations between insomnia and poor health outcomes. But the links between insomnia and heart disease or stroke have been inconsistent," said He.

The meta-analysis assessed the association between insomnia symptoms and incidence or death from cardiovascular disease (acute myocardial infarction, coronary heart disease, heart failure), stroke, or a combination of events.

"Insomnia symptoms included difficulty initiating sleep, difficulty maintaining sleep, early-morning awakening, and non-restorative sleep," said He.

Researchers analysed 15 studies with a total of 160,867 participants. During a median follow-up of three to 29.6 years, there were 11,702 adverse events.

There were significant associations between difficulty initiating sleep, difficulty maintaining sleep, and non-restorative sleep and the risk of heart disease and stroke, with increased relative risks of 1.27, 1.11, and 1.18, respectively, compared to those not experiencing these insomnia symptoms.

There was no association between early-morning awakening and adverse events.

"We found that difficulty initiating sleep, difficulty maintaining sleep, or non-restorative sleep were associated with 27 per cent, 11 per cent, and 18 per cent higher risks of cardiovascular and stroke events, respectively," He said.

"The underlying mechanisms for these links are not completely understood," she said.

Women with insomnia symptoms had a slightly higher risk of cardiovascular and stroke events than men, especially for non-restorative sleep, but the difference between sexes did not reach statistical significance, researchers said.

The research was published in the European Journal of Preventive Cardiology.