Mind, Body & Sleep BLOG

Content published by the Society of Behavioral Sleep Medicine

Why Weight? Go to Sleep!

“Mind, Body, Sleep” SBSM Blog Post February 2020 

Your bed, a treadmill? Kind of.  Sounds like a pretty sweet dream, right?

Turns out, it has a bit of truth: If you want to lose some inches around your waist, try getting some more sleep. But not too much:  . Age appears to affect the relationship between sleep and weight.

In young adults, the relationship between sleep time and BMI is strong: More sleep links to lower BMI. This association progresses into a slightly U-shaped relationship in middle age, when both “short” and “long” sleepers show higher BMIs. More complicated still, the link between total sleep time weakens into later adulthood, such that the oldest, shortest sleepers have the highest BMIs of all other age groups. 

So how much do we need to snooze to lose? The recommended “dose” of sleep depends on age. Children and teens need lots of sleep, ranging from 10-17 hours, while adults aged 26 to 64 need 7-9 hours, and older adults, about 7-8 hours.

However the relationship looks exactly, the research generally agrees: For a lower BMI— don’t weight, go to sleep.

Here are five reasons that may explain why:

  1. More time awake means more time to eat. The longer you stay up, the more opportunities you have to eat. Adults experimentally limited to one hour and 20 minutes of less sleep than controls ate 559 more calories per day than their counterparts, whose intake decreased by 118 calories. The amount and composition of our food also appears to increase over the day, with most calories consumed after 6 PM and a higher percentage coming from fat during late-night versus daytime or early evening hours.

  1. The energy your body doesn’t get from sleeping, it seeks in eating high calorie “junk” foods. Because our body tries to keep things in balance, it compensates for sleep deprivation with high caloric intake, which explains why you probably didn’t binge on arugula during your last all-nighter. In experimental studies of sleep restriction with subsequent ad libitum feeding opportunity(buffet meals and snacks), sleep-deprived adults not only tend to eat more food overall, they also eat more carbs, sweets, and saturated fats than those getting enough sleep. Epidemiological studies reveal similar  findings: “Normal sleepers” (7-8 hours/night) consume more dietary fiber than “short sleepers” (5-6 hours/night) who eat lots of calories more often from fat and refined carbohydrates, which drives insulin resistance.
  2. Under-sleeping may disrupt two key opposing hormones in appetite regulation: Leptin, an appetite-suppressant (anorexigenic), and ghrelin, an appetite-stimulant (orexigenic). Morning, fasting blood samples taken from participants following a night of short (5 hour) vs. long sleep (8 hour) had reduced leptin and elevated ghrelin levels, a combination often (but not always) co-occurring with hyperphagia, or increases in hunger and appetite. Sleep deprivation may also cause hypercortisolemia and other forms of systemic inflammation, contributing to cardiovascular disease, diabetes, and impulsive behaviors, such as emotional eating.
  3. We behave more impulsively without enough sleep. Sleep loss may selectively (de)activate brain regions involved in emotionality and impulsivity. In one study, sleep-deprived adults exhibited more reactivity in their amygdala responding to negative cues than controls. And when compared to their non-sleep-deprived counterparts on functional brain imaging, sleep-deprived adults demonstrated significant functional dysconnectivity between the amygdala (emotional reactivity) and the media prefrontal cortex (impulse control). When the integrity of this connection gets compromised after a poor night’s sleep, obesogenic cues (e.g. that chocolate bar taunting you at check-out, the intoxicating scent of fries at the airport) may feel more difficult to resist.
  4. Fatigue hijacks our motivation. Daytime fatigue due to insufficient or poor sleep can rob us of our motivation to engage in healthy behaviors, including preparing our own meals and/or moving our bodies. Short (vs. long) sleep duration predicted more fast food consumption in one study,and briefer, less intense next-day exercise in another, as examples. And this cycle can quickly get vicious. Over time, reduced activity can promote deconditioning and excessive weight – the biggest risk factor for obstructive sleep apnea (OSA), a common sleep-related breathing condition.

So why weight? Go to sleep!


Later School Start Times

“Mind, Body, Sleep” SBSM Blog Post January 2020 

California becomes the first state to officially promote later school start times and better sleep habits among teenage students. By July 1st, 2022, public middle schools will start no earlier than 8:00am, while high schools will start no earlier than 8:30am.  

The Society of Behavioral Sleep Medicine (SBSM) interviewed Julie Dahl, APRN, the president of the Minnesota Sleep Society. Julie explains the science behind the start school later movement in our podcast interview.  Click here to listen to the podcast.  Highlights from the interview are noted below. 

How many hours of sleep do teenagers need?

According to American Academy of Sleep Medicine (AASM), it is recommended that “teenagers, 13 to 18 years of age, should sleep 8 to 10 hours per 24 hours on a regular basis to promote optimal health and daytime alertness during the critical transition from childhood to adulthood.” 

Additionally, the National Sleep Foundation recommends 7:00am to be the earliest wake-up time for teenagers. “7:00am for teenagers is like 4:00am for adults.”  

Julie points out that teenagers can be night owls by nature. It is quite normal for growing teens to want to sleep late and sleep more in the morning.  

What are some benefits for a later school start time?

During a 3-year research study, which involved over 9000 students from eight public high schools across three different states, researchers found the following results:

  1. Within the schools with a start time after 8:30am, 60% of students received over 8 hours of sleep per school night. 
  2. For teenagers getting more than 8 hours of sleep: Many reported decreased depression symptoms, less use of caffeine, and lower risk of using illegal substances.
  3. For teenagers with a school start time of 8:35am or later, academic performance outcomes and attendance rates were improved while tardiness was reduced.
  4. The rate of teen driver car accidents dropped significantly after the school start time shifted to a later time. 

Later school start times are also associated with improvements in sports performance, reduction in sports injuries, and reduced need for sleep on the weekends. 

What can parents and teenagers do to help optimize sleep?

Julie suggests that the practice of a later school start time should be combined with a sleep education program. She encourages parents and teenagers to watch for signs of lack of sleep, such as grumpiness, poor grades, and/or difficulty waking up in the morning. Parents may want to help their teen(s) make sure to allow enough time for sleep and arrange family priorities around sleep time. Julie encourages teens to “wind-down” both body and mind about 1 to 2 hours before bedtime.  

How can you find more resources and information about this topic?

Julie shares some great resources during our interview.   Click here to view these resources.  For parents, this FAQ sheet and the Evidence Summary section of the Minnesota Sleep Society Teen Sleep Loss Toolkit, may be useful. To advocate for later school start times in your area, visit Start School Later.  


 AASM website: https://aasm.org/california-governor-signs-school-start-time-bill-into-law/

Wahlstrom, K., Dretzke, B., Gordon, M., Peterson, K., Edwards, K., & Gdula, J. (2014). Examining the impact of later high school start times on the health and academic performance of high school students: a multi-site study.

National Sleep Foundation: https://www.sleepfoundation.org/articles/school-start-time-and-sleep

Minnesota Sleep Society: https://www.mnsleep.net/

FAQ Sheet: https://www.mnsleep.net/wp-content/uploads/2017/01/FAQsBetterSleep.pdf

Evidence SUmmary: https://www.mnsleep.net/school-start-time-toolkit/why-improve-sleep-for-teenage-students/evidence-summary-from-the-mn-sleep-society-toolkit/

Sleep Loss Toolkit: https://www.mnsleep.net/school-start-time-toolkit/why-improve-sleep-for-teenage-students/

Start School Later: https://www.startschoollater.net/about-us.html 


Yishan Xu, PhD
Licensed Clinical Psychologist (Mandarin & English)
Psychotherapy & Assessment Group Practice
Mind & Body Garden Psychology Inc

Thank you Julie Dahl, APRN for your time and contribution to this post.