A new study was published yesterday in Cell that made me go "Huh...  that is really cool!".   The study used geotagged data from Twitter users in 1,500 counties across the US to look at daily activity patterns during the week and on weekends.

The "cool" part is obvious, since the study is on circadian rhythm and social jet lag, and I'm geeky enough to enjoy reading studies on the topic.  

The "huh" part was my usual, slightly unsettled feeling in response to the realization that social media usage data reveals a lot that I don't always think about.

So what did this study show?  
First, the researchers were able to graph out the rhythm of when users in a geographic area were mostly asleep. Sure there was still some activity from people working the night shift, but in general, the data shows a big trough during the night. Researchers correlated the 'sleep' time to determine that people were, on average, getting enough sleep. They were able to correlate the county-level tweet data with county level sleep survey data from the Centers for Disease Control (CDC), showing that the Twitter data matched up with regional sleep patterns.

The data also showed what they called "Twitter social jet lag". Social jet lag is the practice of going to be at a normal time during the work week (say 10:30 or 11 pm) but then staying up late on the weekends (at least an hour or two later). Staying up later on the weekend has a similar impact on your body's circadian rhythm as if you traveled a couple of time zones away.  The Twitter data was able to show this for a county by looking at the shift in when Tweets dropped off at night on weekends vs weekdays.  The average Twitter social jet lag for people living in both Central and Eastern time zones was 77 minutes, while on the West Coast it was 56 minutes.  They found that counties that had more elderly people and more college students had lower social jet lag scores, possibly because neither group is getting up early during the work week for a long commute to work.

The researchers also found a correlation between counties with greater social jet lag scores and higher rates of obesity.  This isn't as strange as it might seem at first glance. There is quite a bit of research showing the link between circadian rhythm disruption and weight gain. A study in Cell from 2012 looked specifically at social jet lag and obesity. It concluded, "Our results demonstrate that living “against the clock” may be a factor contributing to the epidemic of obesity. This is of key importance in pending discussions on the implementation of Daylight Saving Time and on work or school times, which all contribute to the amount of social jet lag accrued by an individual. Our data suggest that improving the correspondence between biological and social clocks will contribute to the management of obesity."

So what can we all learn from Twitter time?
I think the study is just one more piece of evidence in an overwhelming avalanche of studies that show the same thing: As a society, we are harming our health by messing with our natural circadian rhythm.  Yes, we are resilient and staying up late one night won't kill us. But...  the overall chronic effects of circadian disruption, due in part to artificial light at night, are causing a public health crisis that needs to be addressed.

What can you do?
Individually:
Block out blue light at night – either through blue blocking glasses or switching to low watt, warm candle-like bulbs.
Get outside more during the day to be exposed to bright light.
Change out your outdoor lighting to cut down on light pollution.

Collectively:
Spread the word! Pass the articles on this website along to a friend, a colleague, or your city councilman. The chronic health effects of disrupted circadian rhythm affect everyone from school kids to the elderly.