People with insomnia may have an increased risk of suffering a heart attack or stroke, a new study suggests.

While previous research has found links between insomnia and various health problems, links with heart attacks and stroke have been inconsistent until now. So Chinese researchers decided to look into this further.

They analysed 15 studies involving almost 161,000 people who were followed up for an average of 29 years.

Insomnia symptoms can include difficulties falling asleep, difficulties staying asleep, early morning waking and non-restorative sleep.

The researchers found a significant link between most insomnia symptoms and the risk of heart attack and stroke. For example, those who regularly had problems falling asleep were 127% more likely to suffer a heart attack or stroke, while those who could not stay asleep were 111% more likely to suffer these cardiac events.

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

"Previous studies have shown that insomnia may change metabolism and endocrine function, increase sympathetic activation, raise blood pressure, and elevate levels of proinflammatory and inflammatory cytokines - all of which are risk factors for cardiovascular disease and stroke," explained the study's first author, Qiao He, of China Medical University.

The study noted that women with insomnia had a slightly higher risk compared to men, although the researchers said this was not statistically significant.

"We cannot conclude that insomnia is more dangerous for women, given the limitations of our research and the lack of a statistically significant difference between sexes. However, we do know that women are more prone to insomnia because of differences in genetics, sex hormones, stress, and reaction to stress. It may therefore be prudent to pay more attention to women's sleep health," they commented.

They added that more public awareness of insomnia is needed, ‘so that people with sleep problems are encouraged to seek help'.

Details of these findings are published in the European Journal of Preventive Cardiology.