A study published earlier this month showed that variability in sleep timing and sleep schedule doubles a person’s risk for metabolic dysfunction by increasing the risk of multiple metabolic abnormalities.  These metabolic abnormalities include:

• High Body Mass Index(BMI)
• High Waist Circumference
• Elevated Systolic Blood Pressure
• Elevated Diastolic Blood Pressure
• Elevated Triglycerides
• Low HDL Cholesterol
• Elevated Fasting Blood Glucose

This is pretty concerning since these abnormalities dramatically increase the risk of multiple chronic diseases including Type 2 diabetes, cardiovascular disease, obesity, Cancer, neurodegenerative diseases, and much more.  It’s also problematic because it’s probably a self-perpetuating problem; circadian rhythms regulate metabolism and metabolism regulates circadian rhythms.

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Circadian rhythms and metabolism

Circadian rhythms help regulate metabolism by converting environmental time-setting cues called zeitgebers in to hormonal outputs that regulate metabolism.  Hormones such as cortisol, insulin, glucagon, and melatonin are all regulated by zeitgebers and impact metabolism.

However, the circadian clocks in all the cells of your body require input from cellular metabolism to help set the separation of use and repair.  For example, increased energy metabolism increases oxidative stress via increased free radical production.  While this happens, repairing cellular damage is less efficient, so cellular repair is separated to the time of day when energy metabolism is at its lowest.

Many people have become keyed in to this relationship so it’s become popular to block inappropriate light at night and perform time-restricted feeding, often referred to as intermittent fasting or 16:8, in an effort to ward off the metabolic dysfunction that comes with circadian disruption.  But many people really don’t see the benefits they should because they’re:

• Inconsistent with their zeitgeber exposure
• Don’t stick to a consistent sleep schedule and routine
• Ignore other important factors that help set timing including stress, timing of physical activity, and poor sleep hygiene

Probably the most significant contributor to this problem is something called social jet lag.  Social jet lag is essentially the common weekly pattern of going to bed and waking up early during the work week and staying up later and sleeping in on the weekends.  This unfortunate pattern is something that’s ingrained in us early as schoolchildren and gets carried in to adulthood.

But you don’t need to have this social jet lag pattern to experience the negative metabolic effects of circadian disruption and sleep variability.  Social jet lag is simply the most common cause.  Given the importance of sleep, it seems inherently reasonable to sleep in on the weekends to make up for lost sleep.  But this doesn’t appear to improve metabolic dysfunction and may actually make it worse by causing circadian disruption.

Conclusion

Having an inconsistent sleep pattern may be an independent risk factor for metabolic dysfunction.  This means that we not only have to pay attention to how much sleep we get and the quality of said sleep, it indicates we probably shouldn’t vary our bedtimes or wake times.

This is likely attributable to circadian disruption, which has been shown to be correlated with metabolic dysfunction.  This underscores the importance of paying attention to circadian rhythms for maintaining a healthy metabolism throughout life.

An excellent study was recently published specifically on the negative consequences of this social jet lag pattern.  I’ll cover that study in a blog on Monday.  It’s much more thorough and an actual randomized clinical trial, so it requires a more in depth analysis.

It actually suggests that sleep variability/social jet lag causes metabolic dysfunction, it’s not just a correlation.  I’ve mentioned numerous times about the detrimental effects of metabolic dysfunction on gut health, specifically in reference to damage to the vagus and enteric nerves.  You don’t wanna miss that one.