Sleeping for an adequate number of hours each day is known to have an enormous positive effect on health. It plays a major role in the functioning of many body systems, including the brain, thinking, and metabolic processes.
Though it is difficult to say exactly how much sleep is enough, the amount varies with the age, co-morbidity, and other environmental factors, such as social and cultural mores. The general consensus is that adults require 7-8 hours of sleep, which may be higher in the elderly. However, 9-10 hours may result in an impaired quality of sleep, which reflects as insomnia or awakenings.
A person who experiences long sleep may be defined as “ an adult who typically sleeps 10 hours or more, but feels well and functions without impairment” (ICDS-3). Hypersomnia is diagnosed as a total sleeping time of over 10 hours, or when an individual regularly or often feels excessively sleepy during the daytime. Hypersomnolence could be defined as sleeping for over 12 hours on working days, and if it is associated with waking up unrested, it is termed severe hypersomnolence. Long sleep occurs in less than 7% of young adults, but is rare in the working age group which is the most busy category.
Risks of oversleeping
Sleep duration and morbidity/mortality have a U-shaped association, which means that normal amounts of sleep are associated with the lowest health risks. Some of the conditions claimed to be linked to excessive sleep include:
- Low energy levels
- Impaired memory
- Diabetes mellitus
- Cardiovascular disease
- Increased mortality by up to a third
While many of these are associated with short sleep, they are even more strongly linked to long sleep.
A note of caution
However, it is important to note that most studies on long sleep are marred by biases of method, confounding factors, and reverse causation. The very definition of long sleep varies between studies. Age is a potent confounding factor, as is the presence of depressive conditions.
In older people, long sleep may be the result rather than the cause of slowly increasing bodily wear and tear leading to fatigue, as well as the lack of adequate activity with aging. If studies are based on a preponderance of elderly subjects, as is quite common, this bias is likely to occur. Another telling fact is that long sleep as well as short sleep are more common in groups with a lower educational standard, which is frequently associated with higher rates of other illnesses and health conditions.
For all these reasons, recent meta-analyses reveal that most of the above-mentioned conditions are not truly associated with long sleep, except for obesity and depression. Individuals with a history of trauma in the past are more prone to depression, which may explain at least in part why they tend to sleep longer. Again, people with depression are more likely to be on sedatives, which increase the total sleep time.
Notwithstanding, some studies have associated excessive sleep in healthy male children with increased life-long mortality from all causes, but not in female children. This requires to be carefully evaluated with respect to confounding factors and other biases which may have crept into the measurement and collection of data, or its analysis.