We all know the drill: Many of us wake up bright and early in the morning Monday through Friday to get out and “make the donuts”.  Then, on the weekends, we stay up late and sleep in for an hour or 2 to catch up.  We know sleep is important, right?  It seemingly makes sense to catch up on the weekends.

But a recently published study seems to cast doubt on the benefits of sleeping in on the weekends.  In fact, the study showed that people who got recovery sleep on the weekends actually fared worse than people who were under chronic sleep restriction.  And by worse I mean their insulin sensitivity tanked by more than double.

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Study layout

In this study, participants were randomized to a control group, a sleep restriction group, or a weekend recovery group.  All groups were given 9 hours of sleep opportunity during 3 baseline days and then subjected to their specific protocol.  The control group was allowed 9 hours of sleep opportunity for all study days.

After the 3 baseline days, participants in the sleep restriction group were given a total of 5 hours of sleep opportunity per night for the length of the study.  In the weekend recovery group, participants were given the same 5 hours of sleep opportunity per night for the first 4 nights.  However, bedtime was delayed 2 hours on night 5 to simulate “Friday” night, and they were allowed unlimited sleep opportunity in to “Saturday” morning and from “Saturday” night in to Sunday morning.  They were then shifted back to 5 hours of sleep opportunity to simulate the following work week.

It’s important to point out that sleep times were selected based on the individual participant’s self-selected sleep time.  So, people weren’t forced in to an unusual sleep pattern.  Insulin sensitivity, dim light melatonin onset and offset, slow wave activity(Deep sleep), calorie intake, change in weight, and subjective hunger were all recorded.

Results of the study showed that both the sleep restriction and weekend recovery groups had a decrease in insulin sensitivity.  Surprisingly, those who were allowed weekend recovery sleep actually saw a 27% decrease in whole body insulin sensitivity, the chronically sleep restricted group only saw a 13% decrease.

A portion of this was dictated by behavior, that behavior being snacking.  The control group had a non-significant increase in snacking after dinner of ~279 cals when compared to baseline.  The sleep restriction group consumed roughly 500 calories more in after dinner snacks during sleep restriction than they did during baseline. (Note: During baseline all groups were restricted to consuming at their caloric needs.  The fact that none of the groups consumed the same number of calories during the study period compared to baseline is indicative that most people overconsume calories as a general practice)

The weekend recovery group was a little more complex.  They consumed roughly 500 calories in after dinner snacks much like the sleep restriction group during the simulated “workweeks”.  However, they consumed fewer calories during the weekend recovery.  They also seemed to consume more pre-dinner snacks during the “workweeks”as well, ~200cals worth.

Interestingly, total calorie intake between all 3 groups was similar throughout the study,  ~1100 cals more/day than during the baseline period.  In fact, the control group consumed the most calories with the sleep restriction group consuming the least.  Despite this, insulin sensitivity in the control group stayed the same throughout while the sleep restriction and weekend recovery groups saw a 13% and 27% decrease in insulin sensitivity, respectively.

Again, a chunk of this probably comes down to an increased calorie intake during inappropriate times, aka nighttime snacking.  But why would the weekend recovery group fare worse than the sleep restriction group given they had more sleep throughout the study?

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The perils of circadian disruption

If we look at sleep in a bubble, you’d think greater sleep restriction would lead to a greater decrease in insulin sensitivity.  But sleep isn’t the only variable we need to be concerned with.  Circadian disruption, independently of sleep, is definitely something we want to keep an eye on.

I’ve mentioned how eating at improper times can cause circadian disruption, and circadian disruption can lead to metabolic dysfunction.  But the people who were getting weekend recovery sleep were actually causing greater circadian disruption than those who were under chronic sleep restriction.

Sure, eating late at night was driving some of this, but changes in light exposure due to the shifting of bedtime and wake times 2 hours later in the weekend recovery group was making it worse by delaying their circadian phase.  And to top it all off, shifting later on the weekends disrupted their sleep on Sunday AND their Monday wake up call.

In effect, they were flying 2 time zones back on Friday, adjusting to the new time zone, and then flying forward 2 time zones on Sunday.  Since it takes a day to adjust for every time zone you jump, they adjusted to the new time just in time to go back to their weekly time zone.  Of course, it will take another 2 days to adjust back to the new workweek time zone.  No wonder they call it social jet lag.

Is Circadian disruption an independent risk factor for metabolic dysfunction?

As it turn out, this isn’t the first time that a study in humans has shown that circadian disruption coupled with sleep restriction leads to a larger drop in insulin sensitivity than just sleep disruption.  In a study comparing sleep restriction under circadian alignment with circadian disruption, the circadian disruption group had a significantly greater drop in insulin sensitivity than the circadian alignment group.  This result occurred despite having the same amount of sleep and consumption of calories.

So why would circadian disruption cause greater metabolic dysfunction than sleep restriction?  Well, it all comes down to the fact that circadian rhythms help regulate your metabolism, and your metabolism helps regulate your circadian rhythms.  There’s also a well-known time of day effect on insulin sensitivity where we process carbohydrates better earlier in the day because glucose stimulated insulin secretion is greater at that time.

Independently of that, circadian disruption causes a decrease in insulin sensitivity.  This probably comes via many mechanisms.  For example, we know that circadian rhythms regulate cortisol output which increases blood glucose by increasing release of glucose from the liver.  Additionally, melatonin appears to play a role in blocking insulin secretion during the night and restoring insulin sensitivity the next day.

The results of this study support the notion that shifting your sleep times on the weekends is a bad idea, and could push you down the path of pre-diabetes and Type 2 diabetes.  At the very least it impairs your insulin sensitivity acutely and should be something you try to avoid doing on a regular basis.

Conclusion

Altering your sleep times on the weekend is a sure way to cause circadian disruption.  The cellular clocks in all of your tissues adjust your metabolism in a time-of-day dependent manner.  Time-of-day information is sent to all of your cells by exposure to various time-setting cues called zeitgebers that translate time-of-day information in to hormonal outputs that allow your tissues to communicate effectively with one another.

Shifting bedtimes and wake times by 2 or more hours on the weekend causes a breakdown in the proper communication between tissues that help regulate blood glucose control.  This primarily includes the pancreas, liver, muscles, fat, adrenals, and brain.  The end results is a decrease in whole-body insulin sensitivity and impaired glucose metabolism.

The results of this study provide support for an epidemiological study I posted last week showing that variations in sleep schedule and total sleep time increase the risk of multiple metabolic abnormalities.  Thus, to maintain a healthy metabolism, it’s important to pay attention to your circadian rhythms by managing your exposure to zeitgebers to keep a proper circadian schedule.

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