Rates of insomnia symptoms such as struggling to get to sleep, waking frequently, or having poor quality sleep, are high among heart failure patients, at up to 73 percent. But it is unclear whether insomnia raises the future risk of heart failure.
Lars Laugsand, M.D., Ph.D., and his team at the Norwegian University of Science and Technology in Trondheim investigated the link.
In the European Heart Journal they explain that insomnia “is considered to be a disorder of chronic activation of stress responses, with sympathetic arousal and activation of the hypothalamic pituitary adrenal axis which is accompanied by increased heart rate, elevated blood pressure, and elevated levels of pro-inﬂammatory cytokines and circulating catecholamines.”
In heart failure, the heart stops pumping enough blood around the body at the correct pressure, usually due to the heart muscle becoming too weak or stiff to work effectively.
The team used figures on insomnia symptoms and cardiovascular risk factors from 54,279 men and women aged 20 to 89 years. All were free from heart failure when they joined the study.
Participants were followed for about 11 years, during which time 1,412 were diagnosed with heart failure.
Participants were asked on joining the study whether they had difficulty going to sleep or staying asleep, and how often they woke up in the morning not feeling refreshed, in other words, non-restorative sleep.
Simultaneously having three or more symptoms of insomnia was linked to a more than threefold increased risk of heart failure, compared with having no insomnia symptoms. This was the case even after adjustment for factors that could affect the results, such as age, sex, marital status, education, shift work, blood pressure, cholesterol, diabetes, body mass index, physical activity, smoking, alcohol, any previous heart attack, depression, and anxiety.
“There was a dose-dependent association between the number of insomnia symptoms and risk of heart failure,” the researchers said. But the risk was only significantly raised for three or more insomnia symptoms, not for one or two symptoms.
“This finding may be interpreted as suggesting that compromising some aspects of sleep may be somehow compensated for, and the net effect on cardiovascular disease may be limited,” they write.
“For example, having difficulty falling asleep might be compensated for by a satisfactory depth and a good continuity of sleep. However, if the initiation of sleep is poor and combined with repeated awakenings and superficial sleep, there may not be any compensatory mechanisms.”
If the results are confirmed by future studies and causation is proved, the researchers believe that checking for insomnia symptoms might spur action to prevent heart disease.
Laugsand stressed that the study does not show that insomnia causes an increased risk of heart failure.
“We do not know whether heart failure is really caused by insomnia, but if it is, insomnia is a potentially treatable condition using strategies such as following simple recommendations concerning sleeping habits, often referred to as sleep hygiene, and several psychological and pharmacological therapies,” he said.
“Evaluation of sleep problems might provide additional information that could be used in prevention of heart failure.”
Laugsand said it is still unclear why insomnia is linked to higher heart failure risk.
“We have some indications that there might be a biological cause, and one possible explanation could be that insomnia activates stress responses in the body that might negatively affect heart function. However, further research is also needed to find the possible mechanisms for this association.”
A 2011 study of the same population group found that insomnia symptoms were also significantly linked to the risk of heart attack. A total of 52,610 men and women were followed up for a first heart attack over 11 years. In this time there were 2,368 heart attacks, recorded in national databases or death registers.
Analysis showed that difficulty initiating sleep almost every night, difficulty maintaining sleep almost every night, and a feeling of nonrestorative sleep more than once a week were each associated with a raised risk of heart attack compared with those who reported never or almost never having these insomnia symptoms.
However, a definitive cause-and-effect relationship has yet to be established. And as the team writes, “further research is needed to better establish the risk associated with insomnia and to reveal the possible pathophysiological mechanisms.”
Laugsand, L. E., Strand, L.B., Platou, C., Vatten, L.J., and Janzsky, I. Insomnia and the risk of incident heart failure: a population study. European Heart Journal 6 March 2013 doi:10.1093/eurheartj/eht019
Laugsand, L. E., Vatten, L.J., Platou, C., Janzsky, I. Insomnia and the risk of acute myocardial infarction: A population study. Circulation, 24 October 2011 doi: 10.1161/CIRCULATIONAHA.111.025858