We’ve talked in the past about circadian rhythms, how there is a daily rhythm of hormone fluctuations that make us more alert during the day, and more sleepy during the night. There are also changes in organ function by time of day. Shiftworkers’ health suffers for being up and active at a time their body is programmed to sleep.

What we haven’t discussed is how these rhythms are established in the first place. Just this week, there was an article published in Science by Lazar and Feng about the circadian rhythm of fat metabolism in the liver.

During the day, molecules modify the liver DNA to reduce fat production. Those molecules leave during the night (so there are 100 at 5am, as opposed to 15000 at 5pm). With those molecules absent, more fat is produced and stored in the liver. The authors conclude “This leads to a circadian rhythm of metabolism that is important, because disruption of this rhythm leads to fatty liver. This may explain in part why altered circadian rhythms in people who do shift work is associated with metabolic disorders.”

There are molecular changes like this happening in many organ systems, multiplying the effect of being out of sync with the natural light-dark cycle.  As our understanding of circadian physiology develops, we’ll be better able to improve the health of shiftworkers.