Category: Science Translation

New Study Finds Link Between Childhood Obesity and Sleep

By Virginia Gurley | Sep 07, 2010

New Study Finds Link Between Childhood Obesity and Sleep

NPR ran an interesting story this morning on childhood obesity and sleep.  To recap briefly, according to national health surveys, obesity rates have doubled in the past 30 years among children ages 2 to 5 years old and tripled among 6 to 11 year olds in the same time period.  University of Washington researcher Janice Bell recently found that infants and toddlers who slept less than 10 hours each night where twice as likely to become overweight or obese in the following 5 years as infants and toddlers who slept 10 hours or more per night.  The study also found that napping did not provide any protection against becoming overweight or obese.  

The reporter also interviewed the head of Stanford University's Center for Sleep Sciences, Emmanuel Mignot, who discussed the possibility that insufficient sleep in early childhood could cause weight gain and obesity through two hormones that increase appetite, leptin and ghrelin.  As we've discussed previously, studies in adults have shown that a single night of sleep reduction significantly decreases leptin and increases calorie intake by 350 to 500 calories.  Dr. Mignot pointed out that sleep restriction decreases leptin and increases ghrelin both of which increase appetite, especially for carbohydrate rich foods. 

The evidence connecting insufficient sleep with increased appetite and weight gain seems pretty strong.  US national data for all adult age groups shows that as overweight and obesity rates have climbed over the past 30 years, average sleep time has been decreasing steadily.  

As strong as this evidence is, I think sleep is just one factor in a bigger issue.  Sleep is an important signal that helps the body synchronize many physiological functions that occur in a circadian rhythm, ie in a 24 hour cycle.  There are, however, many other behavioral and environmental signals such as sunlight exposure, night time lighting and meal timing that affect circadian physiological coordination of metabolic, cardiovascular and energy balance processes.  

Given the widespread prevalence of erratic meals, high stress levels, insufficient sunlight exposure and significant night time light, my hypothesis is that weight gain and obesity, whether in children or adults, are the result of circadian arrhythmicity.  In other words, the disruption of physiological synchronization of metabolic and energy balance processes is resulting from the loss of numerous rhythmic environmental and behavioral signals that the body has evolved to depend on for coordination and appropriate timing of functions critical to health. 

The timing and duration of sleep are very important to weight balance and health, but I don't think it's just about sleep; it's about too many of the rhythms that support our body clocks, like sunlight, darkness, air temperature, and meal, sleep and activity timing being too diminished or erratic for health sustaining physiologic coordination to occur.   

Do You Use a Dawn Simulator?

By Virginia Gurley | Aug 24, 2010

Do You Use a Dawn Simulator?

Dawn simulators are intriguing. In case you’re not familiar with them, dawn simulators are lamps that gradually increase in brightness over the course of 20-30 minutes to reach a maximum brightness at the user’s selected wake-up time. People use them alone, or together with an alarm, to help them wake up in the morning. 

I’ve read antidotal reports from people who have to get up before sunrise and from people who’s sleeping area doesn’t get early morning light that dawn simulators help them wake up feeling more alert.

In several research studies comparing physiological circadian rhythm markers and self-reported alertness when simulators were and were not used, study participants awoke feeling significantly more alert when a dawn simulator was used. In addition, these studies found dawn simulator use was associated with greater peak cortisol upon awakening, and better synchrony between melatonin decline and wake up time. Both of these physiological effects are likely to contribute to the subjective effect of waking up feeling more alert.

In addition to increasing alertness, the effect of simulator use on melatonin timing strongly suggests exposure to dawn light, just prior to waking, helps keep circadian rhythms synchronized to current sunrise time. In the control condition, when dawn simulators were not used, melatonin tended to decline later each morning resulting in a rhythm delay and desynchronization.

These reports and studies of increased waking alertness are consistent with my personal experience of waking up earlier and more easily when camping and sleeping outside. So, when I first came across these studies, I looked into getting a dawn simulator. I didn’t get one, because at the time all the product reviews I read made them sound poorly designed, junky and/or over priced. Writing this article inspired me to look again at what products are available, and it looks like several new ones have come out since my first search.

Anyone willing to share your personal experience using a dawn simulator (no sales pitches from producers please)? Your thoughts and input are greatly appreciated.

L Thorn, et al., 2004. The effect of dawn simulation on the cortisol response to awakening in healthy participants. Psychoneuroendocrinology 29: 925-930

Danilenko KV, et al., 2000.  The Human Circadian Pacemaker Can See by the Dawn's Early Light.  Journal of Biological Rhythms 15:437-446

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