Vitamin Zzzzz

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One of my dad’s favorite sayings when I was growing up was: “One hour of sleep before midnight is worth two hours after.” He would remind me of this when I went to sleep at 3am, woke up at 11am and was bleary eyed despite having had 8 hours of sleep.

Well, a recent study in the journal Obesity helps me to understand why my dad may have been right.

There has been plenty of research linking sleep duration (how long you sleep) to a plethora of health issues including obesity. I have seen many patients eat healthy diets and move their bodies and still have difficulty losing weight. Then they increase their hours of sleep from 5 or 6 hours to 8 or 9 hours, and the weight starts to come off.

However, this new study looks not only at sleep duration but at sleep timing (when you go to sleep) and how this timing affects your weight.

Key Point:

  • You may still be sleeping 7 or 8 hours, but if you go to bed late and get up late in the morning, your weight may still be higher.

The details: The late sleepers in the study (to bed late and up late) ate on average 248 more calories each day than the normal sleepers. And the calories were from twice as much fast food and more full calorie sodas. The late sleepers also ate half as many fruit and vegetables as the normal sleepers.

The researchers are not sure why this happens but it seems that it may have something to do with our circadian rhythms being disrupted. Our body systems are attuned to the daily rhythm of day and night. When we are awake at times when our natural rhythm needs us to sleep, we can wreak havoc with many body systems. There is a lot of research on health issues related to shift workers partly due to circadian rhythms being disrupted.

The study did have another interesting finding:

  • Those people who ate after 8pm weighed more than those who were done eating earlier in the evening. This was true even if sleep duration and sleep timing was accounted for.

This is controversial as other studies have found no difference when people eat calories after 8pm – assuming they are not exceeding their overall caloric needs. More research is needed before we can come to any firm conclusions on this one.

In the meantime, I am taking my dad’s advice. To bed before midnight and up no less than seven hours later. I am definitely not perfect at this – there are certainly times when work, kids or a really good book get in the way. But knowing the importance of both sleep duration and sleep timing helps to keep my sleep habits in check.


Baron KG, et al. Role of Sleep Timing in Caloric Intake and BMI. Obesity. (2011) 19:7;1374-1384.