Researchers find people who get little sleep get fat

Researchers have overturned the long-held theory that too much sleep increases the chance of becoming obese.

A number of epidemiological studies, including the one recently carried out by Columbia University in New York using U.S. government data on 6,115 people, have linked obesity to hormonal changes from lack of sleep.

The Columbia University study found that people who sleep two to four hours a night are 73 percent more likely to be obese than those who get seven to nine hours of sleep. Those who get five or more hours of sleep a night are 50 percent more likely to be obese than normal sleepers. And those who sleep for six hours are 23 percent more likely to be obese.

The preliminary results of a study by Francesco Cappuccio of Warwick Medical School at Warwick University in the U.K. found the same connection in over 28,000 children and 15,000 adults. For both groups, Cappuccio found that shorter sleep duration is associated with an almost two-fold increase in the risk of being obese. These trends are obvious in adults as well as in children as young as 5 years.

Before deliberating this connection, we had better review what obesity is all about. Obesity is a condition in which there is excessive fat (adipose) tissue mass, which increases the risk of contracting a number of serious noninfectious illnesses. The most practical way to measure obesity is by counting your Body Mass Index (BMI), that is by dividing your weight, in kilograms, by the square of your height, in meters. According to the World Health Organization (WHO), the normal BMI ranges from 18.5-24.9 kg/m2. Overweight is defined as having a BMI of 25.0-29.9 kg/m2, whilst obesity is defined as having a BMI of more than 30.0 kg/m2.

Yet for Asian adults, obesity is defined as having a BMI of more than 25.0 kg/m2 and overweight starts from 23.0 kg/m2. This difference is due to the slight difference in body fat composition between Asian and Western people.

More than a billion adults worldwide are overweight according to WHO. Sixty-five percent of American adults are overweight now, according to the Center for Disease Control and Prevention (CDC). The number of obese adults jumped from 15 percent in 1980 to 27 percent in 1999. And there was a three-fold increase in the number of overweight children between 1980 and 2000.

The same trend is true in Indonesia where there was a more than three-fold increase in the number of obese children between 1992 and 1999, according to the National Health Survey.

This epidemic of obesity is serious. The CDC says that one in three American children born in 2000 will develop diabetes, and children under the age of 10 are already developing type 2 diabetes, which is usually only seen in adults in their 40s.

For adults, obesity is linked to the most deadly noninfectious illnesses including heart disease, type II diabetes and cancer, leading to a shorter life span.

Triad of obesity

Obesity is caused by an energy imbalance, in which the energy from food exceeds the energy needed for normal bodily functions and physical activities, including exercise. This excessive energy will be converted into fat, which is stored mainly in the adipose tissue. Adipose tissue, in a sense, is one of the largest organs in the body. In men of normal weight, adipose tissue represents 15-20 percent of body weight, while in women of normal weight, it represents 20-25 percent of total body weight.

Adipose tissue also serves as a protective cushion for the delicate internal organs, allowing the organs to move slightly without friction or irritation. However, if there is too much fat to store, this cushion will enlarge significantly, squeezing the adjacent vital organs and leading to the debilitation of their function.

The accepted rationale for obesity today is that one eats too much and exercises too less. However, body weight is elaborately orchestrated. Researchers have found that sleep loss impacts several hormones related to appetite and food intake.

There are two main hormones that regulate how much you eat: leptin and ghrelin. Leptin is a hormone that is released from full adipose tissue to a specific part of the brain called the hypothalamus as a satiety signal. In the hypothalamus, this signal is relayed to other neural networks resulting in the termination of eating. In contrast, ghrelin, which is released from an empty stomach to the hypothalamus is a signal of hunger. In fact, there are few known regulators of these hormones besides full adipose tissue and an empty stomach. One of the latest findings about this regulator is sleep.

The fact that sleep deprivation leads to obesity is related to these hormones’ regulation. A study conducted by Eve Van Cauter in the Research Laboratory on Sleep, Chronobiology and Neuroendocrinology, at the University of Chicago discovered the altered regulation of these two hormones after sleep deprivation.

She had 12 healthy men of average weight and an average age of 22 come into the hospital laboratory to sleep, and eat dinner and breakfast.

On one occasion, they were limited to four hours in bed for each of two consecutive nights. At another time, they were allowed up to 10 hours in bed for two nights. Their blood was drawn at regular intervals, and they were asked about their hunger.

The findings showed that leptin levels were 18 percent lower and ghrelin levels were 28 percent higher after they had slept for four hours and that the sleep-derived men who had the biggest hormonal changes also said they felt the most hunger and craved carbohydrate-rich food. Besides causing an alteration in these appetite-regulating hormones, it is found, too, that a four-hour sleep per night for six consecutive days lowered body sensitivity to insulin just like a pre-diabetic state according to Van Cauter’s previous study.

She also showed reduced levels of cortisol, which normally surges just before waking from a night’s sleep, energizing people for the day’s demands. The growth hormone level, which plays a role in controlling the body’s proportions of fat and muscle, was reduced as well.

These findings put sleep as a major determinant factor of obesity and general health, along with nutrition and exercise.

Sleep needs vary slightly among the population, but in general most adults need seven to nine hours a night. Experts agree that eight hours of sleep each night is necessary to fully recover from 16 hours of being awake.

Hendy Kristyanto, Contributor

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