In the good old days, sleeping was just something you did thoughtlessly. Not any more. Now sleep duration and patterns have been deconstructed so much that I have started losing sleep worrying about just how much sleep is good for me.
The newest research on sleep duration reports that too much or too little sleep can make you gain weight. Those who slept less than seven hours weighed more than those who slept for nine hours or more. Those who slept between 7 and 8.9 hours each night had a healthy weight.
The study, presented at the international conference of sleep disorders SLEEP 2009 on Friday, was based on data collected from 1,797 twins with a mean age of 36.8. Their body mass index (BMI) — an indicator of body fat calculated by dividing a person’s weight in kg divided by the height in metres squared; (BMI = Weight (kg) / Height (m)2 - was used to measure obesity.
The University of Washington Sleep Institute study found that people who slept over 9 hours had a BMI of over 25.2 kg/m2; and those who slept less than seven hours per night had an average BMI of 26.4 kg/m2.
The relationship between sleep duration and BMI remained after controlling for genetics and shared environment, such as eating and activity levels. A healthy BMI is between 18.5 and 25, with doctors recommending south Asians should keep the number under 23 for health benefits such as lower risk of heart disease and diabetes.
The reasons for the weight gain could be any. Earlier studies have indicated that circadian rhythms — the body clock — regulate metabolism and energy levels in cells and adequate sleep, along with a healthy diet, help maintain the critical balance. According to the researchers from the US National Institutes of Health and the University of California, this partly explained why disruption of sleep patterns increase hunger and cravings, causing obesity.
Chronic sleep deprivation can alter metabolic functions, such as processing and storage of carbohydrates, and by stimulating the release of excess cortisol, a stress hormone. Excess cortisol has been linked to increased abdominal fat, another risk factor for heart disease and diabetes.
Loss of sleep also reduces levels of leptin, a hormone that suppresses appetite, and increases levels of ghrelin, an appetite-stimulating hormone. In combination, it encourages eating.
Weight gain is not the only fallout of sleep patterns. It’s been well established that sustained sleep deprivation increases the risk of almost every known disease, from heart disease (physical stress pushed up blood pressure) to the common cold (lowered immunity).
Earlier this year, researchers reported in the journal Neuron that adequate sleep was essential for learning and memory consolidation, with truncated sleep impairing the brain’s ability to learn and store new information and create memories, with short-term memory being the most affected.
Sleep loss also affects mood, lowering a person’s ability to handle everyday stress, leading to irritability, impatience, inability to concentrate and moodiness.
The amount of sleep essential for rejuvenation varies with people, but experts say seven hours is what one should aim for optimal health.