"Early to bed, early to rise, makes a wo/man healthy, wealthy, and wise," said Benjamin Franklin. It seems that Ben was right, at least when it comes to health, according to researchers in Australia: Early-bird youths stay slimmer than night-owls, even though both groups slept for the same number of hours.
In this study, the behavior of more than 2,200 youths from across Australia aged between 9 and 16 was followed for four days. The bedtimes and wakes times of each participant were recorded, along with the time spent exercising, playing video games, watching television, and engaging in other free time activities. The results were published in the October 1st edition of the journal Sleep.
"Scientists have realized in recent years that children who get less sleep tend to do worse on a variety of health outcomes, including the risk of being overweight and obese. Our study suggests that the timing of sleep is even more important," said Carol Maher, one of the study's authors.
Children who went to bed late and got up late were 1.5 times more likely to become obese than those who went to bed early and got up early. Furthermore, late-nighters were almost twice as likely to be physically inactive and 2.9 times more likely to sit in front of the TV and computer or play video games for more hours than guidelines recommend.
How do we become night-owls?
As humans, we are naturally wired to attune to the rise and fall of the sun. When the sun rises we awaken, and when it sets we are meant to go to bed. This natural tendency to follow the sun can be changed though.
Parents who model night-owl tendencies or allow their children to stay up late can condition their children to become nightowls. Regularly working long past the onset of darkness, being in front of the bright light of computer and cell phone screens frequently at night, and living in noisy households that only get quieter when other family members have gone to bed are also situations that can lead to night-owl behavior patterns. The advent of fire and electricity enabled us to alter the length of time we stay awake, and also made it easier for people to engage in night-owl behavior.
Why do night-owls have a greater disposition to obesity than early-birds?
Staying up late (well after dark) and being in front of bright lights at night produces a physiological stress response, raises blood sugar levels, and encourages people to eat more sugary carbohydrates to keep their brains supplied with energy to help them stay awake. Together these conditions encourage people to eat more calories than they need, which sends them on the fast track to gaining weight and developing diabetes.
Nightowls often get up later than early birds, which can disregulate their eating schedules and shift them to eat more food later in the day when they are less active. Eating more calories at a time when the body is less active, especially at night, leads to the excess energy (calories) being stored as fat and to becoming overweight and obese. In the Australian study, the body-mass index (BMI) scores were higher for night-owls than for early-birds, and night-owls were more likely to be overweight or obese.
The researchers noted that youths who awakened later in the morning were less physically active. It could be that night owls use their day time hours for activities other than exercise and that they don't want to exercise after dark, which is actually very wise. Intense exercise after sunset is very stimulating for the human nervous system and makes it harder for people to get to sleep.
The take-home message
It's not how long you sleep for, it is when you go to sleep that helps to determine your energy levels and body shape. Even though this study was a very short snapshot of activity levels, and needed to be longtitudinal, it has opened the door for other researchers to investigate the long-term effects of nightowl behavioral tendencies on health and body weight. The optimum time to be in bed with the light out is 10pm. If you can make it by 10:30PM then you're doing well.
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Source:
Olds, T. S., Maher, C. A., & Matricciani, L. (2011). Sleep duration or bedtime? Exploring the relationship between sleep habits and weight status and activity patterns. Sleep, 34(10), 1299-1307.
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