Mounting evidence suggests there is a direct relationship between sleep and obesity. While this relationship has been speculated upon for many years, recent advancements in sleep diagnostics, coupled with an increase in research in this area, may help put the issue to bed.
The latest findings from a small French study found that healthy people eat 20 per cent more, on average, after one night of acutely reduced sleep. Other studies have shown that persistent under- and oversleeping results in measurable weight gain over an extended period of time. Given that the average nightly sleep has been declining steadily over the past four decades, the natural conclusion is that sleep deprivation has contributed to the corresponding increase in obesity rates over the same period.
Just how much sleep are we missing? A 2006 National Sleep Foundation Survey in the US found that half of adolescents aged 11 to 17 are sleep deprived, getting one to two hours less sleep than is recommended, on average. Adults do not fare any better, according to several studies conducted in the US showing that adults receive only six of the recommended seven to nine hours of sleep per night, on average.
Sleep deprivation directly and measurably affects the health of adults and children. Both insulin and glucose metabolism are negatively affected, resulting in slower glucose clearance, lower insulin response to glucose, a lower disposition index, and lower insulin sensitivity. All are early markers of health issues, such as diabetes and hyperglycemia, associated with obesity.
There’s more to be concerned about.
“There are two other health issues associated with sleep restriction,” says Dr. Jennifer J. McGrath, Director of the Pediatric Public Health Psychology Laboratory at Concordia University in Montreal, who studies the effects of sleep on children and youth. “First is changes in the appetite-regulation hormones leptin and ghrelin, and second is the effect on the stress-response system.”
Leptin and ghrelin generally work in concert to control hunger. Ghrelin controls appetite stimulation and is secreted by the gut when the body is in need of food energy. Leptin is the appetite suppression hormone, dictating the cessation of eating when the body is satiated. Studies have shown that sleep deprivation relates to lower levels of leptin and higher overall levels of ghrelin.
“This is quite impressive because it changes what people are hungry for, and, in some cases, how much they consume. So they become hungry for more fatty and calorically dense foods, which can lead to weight gain and obesity,” says Dr. McGrath.
The stress hormone, cortisol, has also been shown to be higher in sleep-deprived individuals. In addition, cortisol has a direct link to central adiposity (abdominal fat) and insulin resistance. Sleep deprivation does not always stem from primary causes associated with lifestyle factors such as work or family commitments.
In some cases, obesity itself triggers sleep dysfunction. The most common dysfunction is sleep apnea, a condition in which sleep is disrupted by irregular breathing patterns.
“When obese people have sleep apnea, they have fragmented sleep in which they get secondary sleep deprivation because they are waking up too many times during the night and so they don’t get a full quality night of sleep,” says Dr. Rakesh Bhattacharjee, a Pediatric Sleep Specialist and Respirologist at Toronto’s Hospital for Sick Children.
As one of only three certified pediatric sleep specialists in the country, Dr. Bhattacharjee can attest to the changing profile of children affected by sleep apnea in recent decades.
“The original description of sleep apnea in children was a skinny kid with large tonsils and adenoids, but now we are seeing more obese children, which is the second type of sleep apnea. “Obesity in itself can cause children to be sleepy, which has negative impacts on quality of life and academic performance,” says Dr. Bhattacharjee.
“When you have an obese child with sleep apnea, they tend to be older and they tend to complain more about daytime sleepiness — they tend to behave more like adults. They also have metabolic syndrome and a much higher risk of developing cardiovascular disease. This is quite different from the symptoms of the first type of sleep apnea, which are hyperactivity, irritability, and thinness.”
The risk of sleep apnea increases by 12 per cent for each kg/m2 increase in BMI. It is estimated that two to three per cent of children, and as many as four per cent of adult men and two per cent of adult women, are affected by it.
In many cases, weight loss can cure mild sleep apnea, or at least make management of the problem easier. Treatment for patients with more severe cases of sleep apnea differs for children and adults. In children, the first approach is to remove the tonsils and adenoids, and the second is a treatment with a continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP) device, which keeps the airway open by blowing air into the nose and mouth. CPAP is the first line of treatment in adults, although there are some studies underway looking at the possible benefits of bariatric surgery in alleviating adult sleep apnea.
Dr. McGrath is currently involved in a five year Canadian Institutes of Health Research-funded study to better define the link between sleep deprivation and obesity in Canadian youth aged 10 — 15 years.
“By now, people in the field would agree that there is enough evidence about the cross-sectional relationship and the prospective relationship between sleep and obesity. But what we haven’t done yet is adequately control for possible other factors that could be associated, such as socio-economic status or psycho-social stress, both of which affect sleep.”
The study is using ambulatory EEG recorders to obtain polysomnograph measurements of the children’s sleep stages, which is considered to be the gold standard in assessing sleep and sleep quality. Many previous studies relied on measurements such as sleep duration or sleep logs, which are not as detailed or reliable due to their subjectivity. Other measurements include endocrine function, heart rate and other biological markers, life stress and socio-economic status. The study will wrap in 2013, and it is expected that results will provide much-needed insight into the sleep health of Canadian youth.
Sleep and Socio-Economic Status
Measuring the effects of socio-economic status (SES) can be a tricky business, simply because it pervades all areas of life and health. Some early evidence suggests that the level of SES during childhood has long-term implications for eventual health, even more so than adult SES. Other research suggests that even if SES is improved over time, it may not alter the health trajectory.
The question for Dr. Jennifer J. Mc- Grath, Director of the Pediatric Public Health Psychology Laboratory at Concordia University in Montreal, is exactly how SES affects health.
“We are finding that kids with lower SES have poorer sleep quality and shorter sleep duration. We think it may have to do with structure and routine in the home, changing demands of society, access to convenience foods, or technological advances —kids now have TV or other wired devices in their homes and they are staying up late watching TV, playing games, or texting friends.
“For some children, there are also greater contextual factors — if you live in a high-stress environment where your parents have to work two jobs, there may be less routine or less of a consistent bedtime or more stress. Even factors such as living in a neighbourhood with higher crime or noise pollution can affect your sleep,” says Dr. McGrath.