A new study came out this week in the Journal of Pediatrics that investigated the relationship between teenager sleep patterns, insulin resistance, and being overweight. The study involved 31 overweight teens (average age of 16) and measured sleep patterns for one week during the school year. They participated in an oral glucose tolerance test and an overnight in-lab study of melatonin levels at 30-60 minute intervals.
Longer sleep time, time in bed, and earlier weekday bedtime was found to be associated with better insulin sensitivity.
The average duration of sleep for the group was only 6.6 hours. Teens getting less than that average had higher insulin resistance than those getting more sleep.
The melatonin measurements showed that sleep onset being at an earlier circadian time (meaning closer to the time their body started producing melatonin) was associated with better insulin sensitivity.
These results are completely aligned with previous research on melatonin, insulin resistance, and timing of eating.
Melatonin is not just a ‘sleep hormone’, it is a biological molecule that plays many roles in your body. Melatonin levels rise in the evening and peak in the night. In the morning, exposure to bright light, specifically light in the blue wavelengths (around 480 nm) causes melatonin production to cease for the day.
What does melatonin do?
People who carry genetic variants in a melatonin receptor gene (MTNR1B) are at a much higher risk of type 2 diabetes if they eat later at night. A randomized crossover trial found that eating a late dinner (closer to the time that melatonin rises) caused impaired glucose tolerance. The study also found that those carrying the melatonin receptor variant had an even stronger impairment in glucose tolerance when eating dinner late. (study)
Practical take aways: What can you do to prevent a teenager (or anyone!) from gaining weight due to circadian disruption?
Blocking blue light at night has been shown to increase melatonin levels. So wear a pair of blue-blocking glasses for at least two hours before bed if you are going to be exposed to blue light (bright overhead lights, TV, cell phones, computers). You need to block out all blue light, so just wearing glasses with a light yellow tint isn’t enough at night.
A routine bedtime – both during the week and on the weekend – stabilizes circadian rhythms. Staying up late on weekends and sleeping in the next morning is called social jet lag. Studies show that jet lag or desynchronizing circadian rhythms can cause rapid weight gain. (study)(study)
Eat dinner a little earlier and stop snacking at night. Studies show that time restricted feeding helps with weight regulation. Time restricted feeding means that you limit the time you eat to an 8 to 12-hour ‘window’. For example, if you eat breakfast at 7:30, you would stop eating by 6:30 pm for an 11-hour eating window. (study)(study)
Getting more light during the day causes an increase in melatonin levels at night. Studies show that high levels of light during the day cause an increase in melatonin levels at night. So go outside for a while each morning. (study) (study)