1. What is considered adequate sleep for adults?
According to the American Academy of Sleep Medicine adults ages 18-60 should receive 7 or more hours of sleep per night. Adequate sleep is considered necessary for a healthy lifestyle. One third of adults in the United States do not meet this recommendation for adequate sleep.
2. What is the relationship between sleep duration and obesity?
Obesity rates in adults have progressively increased over the decades. According to the Centers for Disease Control in the United States as of 2017-2018, an estimated 42% of adults are considered obese. Obesity is defined as a Body Mass Index (BMI) over 30. BMI is calculated as weight in kilograms divided by height in meters squared. As obesity rates have increased, sleep duration in adults have decreased. Short sleep duration is considered having less than 7 hours of sleep within 24 hours.
Some studies have shown that an insufficient sleep duration increases the chance of obesity by 45%.1 Other studies have demonstrated a reverse J association between sleep duration and obesity.2 Meaning that persons with a short sleep duration showed an increased risk of obesity. However, a long sleep duration was not found to be associated with increased risk of obesity. Adults receiving 7-8 hours per day of sleep were found to have the lowest rate of obesity. For each one hour decreased in sleep from ideal the obesity rate increased by 9%. Short sleep duration has also been found to be associated with increased waist circumference.1
3. How does short sleep duration cause obesity?
Short sleep duration may lead to increased fatigue, resulting in decreased physical activity which leads to decreased energy expenditure and increased obesity. In addition, lab studies have demonstrated high ghrelin levels in sleep deprived animals.3 Ghrelin is often referred to as the “hunger hormone “. Ghrelin is produced in the gut and small intestine and helps to stimulate appetite. Short sleep duration has also been associated with increased cortisol hormonal levels which can lead to increased food intake and increased visceral fat accumulation.
4. What other sleep disorders are related to obesity?
Obstructive sleep apnea (OSA) is a sleep disorder and a form of sleep disordered breathing. OSA occurs when the upper airway becomes partially or completely blocked during sleep leading to restriction in airway flow. Diagnosing OSA is done by performing a nocturnal polysomnography or a sleep study. Increasing BMI has been associated with worsening OSA. Weight loss has been shown to decrease the severity of OSA.3 Obesity contributes to excess fat on the neck which may cause compression of the upper airway during sleep leading to OSA. Obesity may also affect upper airway functions such as lung volume and respiratory drive contributing to OSA.
5. What is stress?
Stress is defined as a negative emotional experience accompanied by biochemical, physiological, cognitive, and behavioral changes.4
6. Are stress and obesity related?
Yes, many studies have demonstrated that increased stress is correlated with increasing obesity.
7. How does stress contribute to obesity?
Stress has been associated with decreased sleep duration and therefore increased obesity. High stress levels have been also been linked with decreased physical activity, increased food wanting and increased food intake in humans.4 Hormones such as dopamine- which can trigger food seeking and cortisol-which can promote hunger have also been found to be increased in response to stress. A persons’ ability to self-regulate and control behavior may also be affected by stress. Decreased ability of self-regulation secondary to stress can result in overeating and or making unhealthy food choices.
8. Can stress affect weight loss?
Increased stress levels and low mood have been shown to affect the success of weight loss and to increase the dropout rates in weight loss programs.5