Less than 6 hours of sleep a night linked to increas...

"Getting less than 6 hours of sleep could double – or even triple – your risk of dying from heart disease or cancer, especially if you have chronic diseases," reports Mail Online.

This stark warning is taken from US research that analysed the sleep of around 1,600 adults. Participants had their sleep monitored during a single night in a sleep laboratory during the 1990s. Researchers kept track of the group up to 2017 and found that in general, those who slept less than 6 hours were more likely to have died. They also found there was an increased risk of early death among people with long-term (chronic) conditions, such as high blood pressure or heart disease, who slept for less than 6 hours each night.

There are several limitations to this study. In particular, the participants only had their sleep measured once and in an artificial setting, which may not have been representative of their sleep patterns over time. The researchers did not get the same results when they looked at how long participants said they usually slept.

The researchers did take steps to account for other factors, such as physical and mental health conditions, which could be influencing the results. However, various health and lifestyle factors could be playing a role in the links they identified.

Despite this study's limitations, we know that getting enough sleep is important for good health. If you are having trouble sleeping, you can try simple steps such as reducing caffeine consumption and getting more exercise. Find more tips on how to get to sleep.

If you have persistent problems with insomnia, see a GP.

Where did the story come from?

The study was by a group of researchers from Pennsylvania State University College of Medicine, US.

It was funded by the American Heart Association and the National Institutes of Health.

The study was published in the peer-reviewed Journal of the American Heart Association, and is open access, meaning it is free to read online.

The UK media's coverage focused on the dramatic headline figures of doubling or tripling risk. However, there is no mention of the limitations to this study, which mean the findings are not conclusive.

What kind of research was this?

This analysis was part of the Penn State Adult Cohort study, which was a cohort study tracking health outcomes in the US. It looked at whether the amount of sleep that people with cardiovascular risk factors had each night might influence their risk of early death. The researchers say that previous studies on the topic have only asked people how long they slept for, and not assessed this objectively in a sleep laboratory.

An observational study is the best way to assess such a link, as it would not be practical, feasible or acceptable to ask people to have a specific amount of sleep over a long time, just for the purposes of research.

The main challenge with this type of study is that it is difficult to single out the health impact of one aspect of people's complex lives. People who have more sleep may also differ in other ways from those who have less. They may be more health conscious or be less stressed, and these other factors could influence the results. Researchers can take steps to make this less of an issue, but it's not possible to be certain that all other influences have been removed.

What did the research involve?

The researchers selected participants at random from the Penn State Adult Cohort study. These people had their sleep duration tested in a laboratory. Researchers then followed up participants over time and looked for links between cause of death among those who had died and how many hours those people usually slept for each night.

The participants were enrolled during the 1990s and all went to a sleep laboratory overnight to allow researchers to monitor them. This included taking people's blood pressure, blood sugar levels, recording their body mass index (BMI), and asking them if they were taking medicines for high blood pressure or type 2 diabetes. Participants were also asked whether they had ever been diagnosed with heart disease or stroke by a doctor. The researchers used sleep monitors overnight to identify who slept less than 6 hours (about half of the participants) and who slept for longer. They also asked participants how long they usually slept for each night.

Between 2014 and 2017 the researchers identified participants who had since died, and their cause of death, using the National Death Index of the US Centers for Disease Control and Prevention.

They were able to analyse data for 1,654 participants, who were aged 20 and 74 years at the start of the study (average 47.5 years). Participants had been followed for an average of about 19 years by the end of the study.

The researchers compared deaths among those with different long-term conditions, and those measured to be shorter and longer sleepers, taking into account a range of confounding factors that could impact the results, including:

age
sex
race
education
BMI
caffeine, tobacco and alcohol consumption
whether a person's sleep results indicated they had sleep apnoea
other physical or mental health conditions

The researchers also checked whether they got different results if they used the participants' own reports about how long they usually slept for at night.

What were the basic results?

At the start of the study, almost half of the participants had either high blood pressure or type 2 diabetes, and 14% had heart disease or had experienced a stroke in the past. By the end of the study about 1 in 3 participants (31%) had died.

The researchers found that about 40% of those who were measured as having less than 6 hours of sleep at night died during follow-up, compared with about 22% of those who were measured as sleeping longer than this.

The researchers found that measured sleep also impacted the link between cardiovascular conditions, risk factors and death:

Among people who slept less than 6 hours, those with high blood pressure or type 2 diabetes were about twice as likely to die during follow-up (hazard ratio [HR] 2.14, 95% confidence interval [CI] 1.52 to 3.02).
Among people who slept less than 6 hours, those who had heart disease or past stroke were about 3 times more likely to die during follow-up (HR 3.17, 95% CI 2.16 to 4.65).
In both cases, the increase in risk was not seen among those who slept more than 6 hours.

When looking at specific causes of death:

In people whose measured sleep was less than 6 hours, those who had high blood pressure or type 2 diabetes were more likely to die from heart disease or stroke (HR 1.83, 95% CI 1.07 to 3.13), but this link was not found in those who slept for longer than this. A similar pattern was found for deaths from other causes.
In people whose measured sleep was less than 6 hours, those who had heart disease or past stroke were more likely to die from cancer (HR 2.92, 95% CI 1.28 to 6.65), but this link was not found in those who slept for longer than this. This difference in risk across those sleeping for shorter or longer was not seen for deaths from other causes.

How did the researchers interpret the results?

The researchers concluded that among middle-aged adults who have high blood pressure or type 2 diabetes, sleeping for less than 6 hours at night predicts a greater risk of earlier death. Among middle-aged adults who have heart disease or past stroke, sleeping for less than 6 hours at night predicts a greater risk of death from cancer. They say that people with these long-term conditions who are getting little sleep may benefit from treatments to help them sleep for longer.

Conclusion

This study suggests that among those with risk factors for dying from cardiovascular disease, poor sleep could increase risk of earlier death.

The study has some strengths, including the fact that it set out to collect some of the data (mainly information on sleep) rather than relying on data that had already been collected for other purposes. However, its limitations mean that its findings are not conclusive.

While measuring sleep objectively in a laboratory does avoid people inaccurately reporting their own sleep, it does come with its own limitations. The participants were only assessed for one night and this assessment took place in a sleep laboratory. The results may not be representative of their normal sleep patterns at home, or over a longer period. Notably the researchers found that they did not get the same results when they asked people how long they usually slept for.

The study was relatively small, particularly when it came to analysing deaths from specific causes. For example, only 21 people with heart disease or previous stroke died from cancer. This means that the analyses of this outcome may not be very robust.

As with all cohort studies, we cannot be sure that sleep alone is the cause of the links seen. While the researchers tried to take into account some relevant factors in their analyses, these and others could still be having an effect.

The researchers suggest that those with high blood pressure, type 2 diabetes, heart disease or previous stroke who get less than 6 hours sleep at night (according to sleep laboratory measurements) "may benefit from targeted treatments to lengthen sleep and improve their long‐term [outcomes]". However, further studies would be needed to test whether this would be the case.

Overall, despite this study's limitations, we know that getting enough sleep is important for our health. There are relatively simple steps people can take to improve their sleep, such as reducing caffeine and alcohol intake and doing more exercise. For people who have sleep problems that persist despite trying these things, or who are worried about their sleep, they should talk to a GP.