Laziness and lack of sleep can shorten your life, especially when combined, study says

You already know that smoking is bad for you and that drinking too much alcohol may shorten your life. Now a new study says that spending too much time in a chair and depriving yourself of necessary sleep should join a short list of behaviors known to increase your risk of premature death.

Sedentary time and lack of sleep were damaging in their own right, but when combined with more traditional risk factors, they had a multiplier effect that made an early death far more likely.

The findings, published Tuesday in the journal PLOS Medicine, make clear that “some risk behaviors tend to cluster, particularly in certain patterns, and that the joint risk could be much higher than the sum of the individual risks,” the study authors wrote.

See the most-read stories in Science this hour >>

For instance, smoking was the most dangerous single risk factor among the six studied — the small number of people for whom smoking was their only vice were 90% more likely to die during the course of the study than were people with practiced clean living across the board. People who reported high alcohol consumption — more than 14 alcoholic drinks per week — as their sole risk factor did not seem to be putting their lives in danger. But for those who combined heavy drinking with smoking, the risk of premature death was nearly tripled. And when lack of sleep was added to the mix, the odds of an early death were nearly five times greater — even though lack of sleep by itself had only a slight effect on mortality.

These numbers are based on the lives, and sometimes deaths, of 231,048 Australians from Sydney and rest of the state of New South Wales. They enrolled in the 45 and Up Study between 2006 and 2009, answering questions about their smoking history, eating and drinking habits, exercise routines, sedentary time and sleep duration. The study volunteers were tracked until the middle of 2014; during that time, 15,635 died.

When they joined the study, 7.2% of the participants were smokers, 19.1% were heavy drinkers, 17.2% had a poor diet, 22.9% got too little exercise, 25% spent more than 7 hours sitting each day and 23.1% got either too little or too much sleep. Nearly one-third (31.2%) of the volunteers did not engage in any of these risk factors, and 36.7 reported only one. However, 21.4% of them admitted to two of these bad habits, 8.1% admitted to three, 2.1% reported four, 0.4% had five and 0.04% engaged in all six.

Except for heavy drinking, each of the six behaviors was associated with at least a slight increased risk of death during the study period, the researchers found. Smoking was the most dangerous, followed by lack of exercise.

After accounting for factors such as age, gender, education and other demographic factors, the researchers saw a clear pattern: The more deviations a person had from a clean lifestyle, the greater his or her risk of premature death. Compared to people with no risk factors, those with just one were 27% more likely to die during the course of the study, and those with two had a 73% increased risk of death. At the other end of the spectrum, people with five risk factors were 4.61 times more likely to die, and those with all six were 5.38 times more likely.

Some combinations were more deadly than others, the researchers found. Those who blended insufficient exercise with prolonged sitting were 2.42 times more likely to die during the study, and those who were also guilty of sleeping for too many hours were 4.23 times more likely die by the time the study ended.

“These findings suggest there is a ‘synergistic effect’ among risk factors,” the study authors wrote.

The authors acknowledged that it was up to each volunteer to report on their smoking, sitting, sleeping and other behaviors, and some of them might have shaded the truth to impress the researchers. If so, the study results probably underestimate the true effects of the risk factors, they wrote.

The authors added that their results would be more meaningful if they tracked people’s risks behaviors over time, and if they could link those behaviors to heart disease or other specific causes of death. That information was not available when the analysis was done, they wrote.

Follow me on Twitter @LATkarenkaplan and “like” Los Angeles Times Science & Health on Facebook.

MORE FROM SCIENCE

American teens exercise a mere 39 minutes a day, study finds

Karma bites back: Hating on the elderly may put you at risk of Alzheimer’s

There’s no such thing as a ‘male brain’ or ‘female brain,’ and scientists have the scans to prove it