Insomnia "can triple your risk of heart failure", the Daily Mail reported today.
Try not to lose sleep over this story. The Mail has chosen the most startling figure it can find. Fortunately, the results of the research are less worrying.
The Mail’s story is based on a huge study of the population of a region of Norway. The study assessed Norwegians’ sleep quality, health and lifestyle, and tracked their risk of heart failure during the subsequent 11 years.
Researchers found a significant trend for higher risk of heart failure as the number of insomnia symptoms increased. People who reported three symptoms – trouble getting to sleep, trouble staying asleep and having poor quality sleep – were at more than four times the risk of heart failure compared with those without insomnia symptoms.
While this is a major piece of research, it does not prove that insomnia causes heart failure. The researchers' analyses of individual insomnia symptoms and the total number of insomnia symptoms did not give a clearly significant result each time. This makes it difficult to see if a true direct relationship exists.
Any link between poorer sleep and heart failure risk could have been influenced by a host of health and lifestyle factors that the study has not been able to take into account, including sleep apnoea.
Overall, the findings are interesting but no firm conclusions can be drawn about the link between insomnia and risk of heart failure.
Where did the story come from?
The study was carried out by researchers from the Norwegian University of Science and Technology, the Nord-Trøndelag Health Trust, Norway, and the Karolinska Institutet, Sweden. The authors were funded by various grants from public institutions in the two countries.
The study was published in the peer-reviewed European Heart Journal.
Most coverage in the media was fair, with both the BBC and the Mail including comments from UK experts. The origin of the Mail’s claim that having insomnia or a bad night’s sleep “can triple your risk of heart failure” is unclear, however. The researchers conducted many analyses including different patterns of insomnia and adjusting for different confounding factors, but there appears to be no single result that equals a tripled risk.
What kind of research was this?
This research used data from the Nord-Trøndelag Health study (HUNT study). This large study involved a three-phase health survey of the population of the Nord-Trøndelag region of Norway. The study has collected a large volume of sociodemographic, health and lifestyle data. The current research used this data to examine the association between self-reported insomnia and the risk of heart failure in more than 54,000 people.
A cohort study such as this can be useful for looking at associations between certain lifestyle factors and later health outcomes. However, cohort studies cannot prove causality. In this cohort, although a large amount of data was collected, the study was not set up with the aim of investigating any specific risk factor or disease outcome. Using the data gathered to examine these associations (as has been done in this study) makes it even harder to ensure that all potential confounding factors have been taken into account.
The authors say that while insomnia symptoms have been found to be common among people who have established heart failure, few studies have looked at whether insomnia might play a part in increasing later risk of heart failure among people who are initially free of the disease. They point out that insomnia is associated with increased heart rate, a rise in blood pressure and elevated levels of certain chemicals associated with inflammation.
What did the research involve?
In this study, the researchers used data from the second wave of the HUNT study, which collected detailed information about the health of 65,215 adult men and women between 1995 and 1997.
Information was collected from the participants using a self-administered questionnaire, which had three questions related to insomnia:
- ‘Have you had difficulties falling asleep in the last month?’ Response options were: ‘never/occasionally/often/almost every night’.
- ‘During the last month, have you woken up too early and not been able to get back to sleep?’ Response options were: ‘never/occasionally/often/almost every night’.
- ‘How often do you suffer from poor sleep?’ Response options were: ‘never or a few times a year/one to two times per month/about once a week/more than once a week’. This question was restricted to people who were 20–69 years of age.
A total of 54,403 participants (83.4%) answered one or more of the insomnia questions. The questionnaire also included detailed questions on health, medical history, lifestyle factors (such as physical activity and use of alcohol and smoking) and use of medication. Participants also had a clinical examination that included assessment of:
- blood pressure
- waist circumference
Participants were asked about symptoms of depression and anxiety, using a standard anxiety and depression scale.
The researchers excluded 124 people whose medical records indicated they already had heart failure, and for the remaining 54,279 people they looked at the follow-up data collected in 2008 (around 11 years later), to find out who developed heart failure. Hospital admissions for heart failure were identified by linking with medical records. Deaths due to heart failure were identified using a national death registry.
Researchers used statistical methods to analyse the association between self-reported insomnia in 1995-97 and later development of heart failure by 2008. They also analysed the effect of each individual insomnia symptom (falling asleep, staying asleep and feeling of poor sleep), and the cumulative number of symptoms. The researchers adjusted the results for potential confounding factors including cardiovascular risk factors such as history of heart attack, high blood pressure, low physical activity, high BMI, high cholesterol and lifestyle factors. A separate analysis also adjusted results for depression and anxiety, which are associated with sleep disorders.
What were the basic results?
Researchers found that:
- 3.4% of people reported having problems initiating sleep every night
- 2.5% reported problems staying asleep almost every night
- 8.1% reported poor sleep more than once a week
A total of 1,412 cases of heart failure occurred during an average follow-up of 11.3 years.
When looking at each individual insomnia symptom the researchers found no significant relationships between any of these individual symptoms and risk of heart failure when adjusting for cardiovascular risk factors. They also found no significant relationships when additionally adjusting for depression and anxiety.
When the researchers looked at total number of insomnia symptoms, they found a general significant trend for an increase in risk of heart failure with the greater number of symptoms reported (after adjusting for cardiovascular risk factors).
They found no significant association between one or two insomnia symptoms and risk of heart failure.
However, people with three symptoms were more than four times more likely to develop heart failure (hazard ratio 4.53, 95% confidence interval 1.99-10.31). Adjusting for depression and anxiety slightly changed the significance of the results. The overall trend for an increase in risk of heart failure with a greater number of symptoms became non-significant when adjusting for depression, but became significant again when also adjusting for anxiety. This makes it quite difficult to draw firm conclusions from the results.
How did the researchers interpret the results?
The researchers say that insomnia is associated with a risk of heart failure. If the results are confirmed by other studies, evaluating insomnia symptoms might become part of strategies to prevent cardiovascular disease, they argue.
This study uses data from a large population cohort and benefits from its large size and long duration of follow-up. It also included thorough assessment of both insomnia symptoms and other health and lifestyle factors.
Researchers tried to take into account the established risk factors for heart failure, but the research has limitations, some of which the researchers note. These limitations include that:
- When analysing the individual symptoms and total symptoms, some results showed significant associations and some didn’t. This significance also varied when the analyses were adjusted for depression and then for anxiety. This makes it difficult to get a clear picture of whether there is any direct link between insomnia and heart failure.
- Although the researchers adjusted their results for several established cardiovascular risk factors and for mental health factors, it is possible that the influence of these have not been fully taken into account, or that some unmeasured factors may have influenced the results.
- Insomnia was only evaluated once at the beginning of the study. This means that any possible changes in self-reported insomnia were not measured in the study.
- Researchers did not measure insomnia objectively, but relied on people self-reporting. This meant that they had no information on sleep apnoea, a condition that is associated with sleep problems and with risk of cardiovascular disease. As such, this is a specific confounder that has not been taken into account.
- There are some factors that may limit whether these findings are applicable to the UK population. Most parts of Norway have a more northerly latitude than most parts of the UK and so citizens of Norway may have different sleeping patterns from UK citizens. People from Norway may also have different underlying heart failure risk. Also, the question on poor sleep was restricted to people younger than 70 years, so the results on this symptom and also on the cumulative number of insomnia symptoms, cannot be generalised to older people.
Although this study provides some clues about the link between insomnia and heart failure, it does not prove that insomnia causes heart failure.
We know that getting enough sleep is important for physical and mental wellbeing. Lifestyle changes – such as having a relaxation routine and avoiding caffeine at the end of the day – can help. There are treatments available and if insomnia is affecting your daily life, you should speak to your GP about it.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Daily Mail, 6 March 2013
BBC News, 6 March 2013
Daily Express, 6 March 2013
Links to the science
European Heart Journal. Published online March 5 2013