Does getting too much or too little sleep affect your health—or even how long you are likely to live?

Even though Lewis Terman began researching the relationship between sleep and health in 1913,  how much or little sleep you need to have a healthy life is still open to debate. Certainly, researchers have long known that sleep problems are linked to a wide range of medical issues. Whether it be increased depression, anxiety, or hostility; work-related problems; loneliness; or poor physical health, numerous studies have demonstrated the damage that can be caused by lack of sleep. The amount of sleep one gets can also impact medical problems such as diabetes, high blood pressure, and cardiovascular disease.

Perhaps even more important, not getting enough sleep at night can be a good predictor of the risk of premature death. As early as 1964, a study showed that adult males sleeping an average of seven hours of sleep at night had the lowest mortality risk. However, getting too much sleep can also have a negative impact on mortality: A 1979 study found that adults who slept more than 10 hours (or fewer than four) had an increased mortality risk. Reviews of different studies examining sleep duration found that people getting too much sleep were also at increased risk for cardiovascular disease and cancer. (While getting too little sleep was also linked to higher mortality, there was no clear pattern involving cause of death.)

All of this raises the question of why too much or too little sleep leads to health problems. To rule out other possibilities and to understand the long-term impact of sleep problems on overall mortality, a new study published in Health Psychology looks at the link between sleep duration (number of hours of sleep each night) and life expectancy. In the study, Katherine A. Duggan and a team of researchers at the University of California, Riverside and the University of Pennsylvania used data taken from the Terman Life Cycle Study. Launched by Terman between 1917 and 1922, the study compiled a sample of 1,528 high-IQ children who were tracked into the present era to study how their lives unfolded. By organizing the most ambitious longitudinal study of its kind, Terman (who died in 1956) hoped to create a database showing how children developed from early childhood into old age. While many of his eventual conclusions about intelligence and long-term success remain controversial, the data on how the "Termites" changed over time is still an important resource for developmental psychology. 

In the study by Duggan and her colleagues, data from the Terman study was supplemented with death certificates identifying the subjects' cause of death. The study was limited to subjects born between 1904 and 1915 with a final sample of 1,145 people. Based on their analysis of the results, the researchers concluded that males of all ages who got too much or too little sleep—averaging one, two, or three hours more or less of average nightly sleep than others in the study—were at increased risk of dying throughout their lifespan. This appears consistent with previous research finding a U-shaped relationship between sleep and overall health.    

While other studies have questioned whether the relationship between sleep problems and health may be related to underlying medical problems, using the Terman subjects meant that many undiagnosed diseases could be ruled out, since the groups was typically healthier than the general population. The analysis showed that sleep problems seemed to be linked to increased risk of cardiovascular disease and infection in males. This might suggest that disturbances in sleep can affect overall resistance as well as problems with heart inflammation.

However, the impact of sleep disturbances on overall mortality for females was harder to determine. While some previous studies have found no differences between men and women in terms of how sleep problems affect health, much of the research literature suggests that males may be more vulnerable to sleep problems. Why this would be is still unknown. 

It is also important to point out that the study only included information on the amount of sleep the participants in the study received as children. Since there was no information on how much sleep they got as adults, the connection between possible childhood sleep problems and adult sleep issues could not be determined. Still, the relationship between childhood sleep problems and long-term mortality rates (at least in males) appears strong.

What are the implications of these study findings for us?

Sleep problems in children can lead to major health problems as long as six decades later. While the recommended amount of nightly sleep for children has actually decreased in recent years, the potential health risks faced by both children and adults who get too much or too little sleep need to be recognized. The research also suggests that sleep problems such as insomnia and sleep apnea can be far more serious than most people realize.   

So spare a thought to how you are sleeping at night and whether your sleep is all that it needs to be. Your life may depend on it.

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