The Disconnect Between Biological Time and Standard Time Reduces Health

In Poor Sleep Makes People Poor I discussed an important paper by Maulik Jagnani showing how India’s single time zone creates a big disconnect between biological time as given by light cues and clock time. The disconnects impedes sleep patterns and reduces human capital for those most effected.

In a new paper in the Journal of Health Economics, Sunset Time and the Economic Effects of Social Jetlag Giuntella and Mazzonna show that the same types of effects can be observed in the United States.

The rapid evolution into a 24h society challenges individuals’ ability to conciliate work schedules and biological needs. Epidemiological research suggests that social and biological time are increasingly drifting apart (“social jetlag”). This study uses a spatial regression discontinuity design to estimate the economic cost of the misalignment between social and biological rhythms arising at the border of a time-zone in the presence of relatively rigid social schedules (e.g., work and school schedules). Exploiting the discontinuity in the timing of natural light at a time-zone boundary, we find that an extra hour of natural light in the evening reduces sleep duration by an average of 19 minutes and increases the likelihood of reporting insufficient sleep. Using data drawn from the Centers for Disease Control and Prevention and the US Census, we find that the discontinuity in the timing of natural light has significant effects on health outcomes typically associated with circadian rhythms disruptions (e.g., obesity, diabetes, cardiovascular diseases, and breast cancer) and economic performance (per capita income). We provide a lower bound estimate of the health care costs and productivity losses associated with these effects.

Hat tip: Kevin Lewis.


"[W]e find that an extra hour of natural light in the evening reduces sleep duration by an average of 19 minutes and increases the likelihood of reporting insufficient sleep". Does this also apply to daylight saving time? There's momentum to make daylight saving time year-round, which would exacerbate sleep deprivation and the adverse conditions associated with it. I am a morning person and I detest daylight saving time. My view is that if the clock is to be moved an hour, it should fall back in the spring and summer not spring forward.

That was my question also: the time-zone discontinuity gives cross-sectional comparisons but not a time-series comparison.

On the one hand, I've read that people who live in far northern latitudes can suffer from sleep deprivation during the long daylight hours of summer (an episode of the TV show "Northern Exposure" was devoted to exactly this, as former New Yorker Dr. Fleischman becomes manic and hyperactive due to the lack of darkness). On the other hand, I think most people would agree they prefer the long daylight to the long darkness of winter. So maybe people are getting less sleep -- but are happier with that extra evening hour of sunlight? I know that I prefer it to an extra hour of sunlight in the morning (but that's partly because I'm not a morning person anyway).

And that's why China is doing so poorly??? I am somewhat skeptical. But I think we would do well to all go to Greenwich Mean Time, and to adjust local start times to match the sun. We DON'T want to go back to the early USA situation where you took the train to Chicago and local time changed by, I think, a minute every thirteen miles!

Contrarian take - would an early USA situation really be that bad given the technology in our pockets?

Reverting to this would be easier today than it would have been 20 years ago. Your phone keeps track of the local time, while your maps app could tell you what time it will be in your new location. Might this be worth the slight inconvenience if it got everyone on better sleep schedules?

You clearly don't manage schedules across multiple time zones. Technology is terrible at handling this.

You are correct on what I don't manage. What current shortfalls are there in terms of scheduling? Could better technology solve them?

It would, for a few reasons.

First, the obvious: There are 4 time zones in the continental USA. Simple math tells us that there should be 210 to 240 time zones if we go by minutes. Trying to coordinate schedules with 210 confounding factors would be a nightmare. Trying to set up a conference call would be horrific. And no, better tech couldn't solve it--because we don't like in technology. People go out to lunch. People make plans with friends. And sure, a minute or two won't matter, but 20 minutes can be a huge issue.

Where this would get really problematic is when you travel. If I travel from, say, Alabama to Mississippi, how many time zones do I cross? How do I figure that out? If I'm 20 minutes late for a conference call, that call is canceled in many cases.

The second is more subtle. Look at a map of time zones and you'll notice they aren't straight lines. Time zones are affected by politics, just like everything else. This isn't too bad when you have 4 time zones; if you have 210 time zones, it quickly becomes a nightmare. Cities, to coordinate the myriads of things they need to coordinate, will want to be in the same time zone--which means you may have a section of a city that's 3 or 4 time zones apart from the sections outside the city. And what do you do when new territory is incorporated into the city? Which time zone does it go under? Again, a minute or two may not matter--unless you're setting up, say, an automated stock exchange program or something similar.

And regardless of what your answer is, the fact remains that we have 210 (or more) lines of political contention. How much time and how many resources is this going to cost us? Remember, this isn't 210 disputes--it's 210 CAUSES FOR disputes.

Come to think of it, that's a good selling point: with the thousands or tens of thousands of debates this would cause, government would slow down even more than its currant glacial pace. Maybe a way to institute minarchism?

Well, I am relying on a slight technological leap here. The phone tells you when you're gonna get where, in terms of minutes and time zone changes. Hardly a major programming issue.

This should fix lunch, plans with friends, and driving between states. In fact, if you go in the other direction and head to GA from AL, you're already doing this! And that's a much larger jump too - more zones make that arbitrary line much less disruptive.

Driving up the transaction costs of conference calls and up-to-the-minute automated trading hardly sounds like a major loss to me. Might even be a weird way of taxing negative externalities. I would love if managers had to think twice before setting up the next time suck.

The government issue might be serious and is worth considering. I don't think cities should have a lot of say here and the lines should track solar noon. But that's probably a bit utopian.

"The phone tells you when you're gonna get where, in terms of minutes and time zone changes. "

Except that not all do. Remember, just because technology is COMMON does not mean it's UBIQUITOUS. I use a flip phone, because I dislike the disruptive nature of smart phones, and it's got the navigational capacity of a squirrel with a concussion. Some of us even use paper maps.

"...more zones make that arbitrary line much less disruptive."

This is a fundamental error to your argument. You want to decrease disruption by increasing the number of disruptions, but reducing the scale of disruptions. This assumes that disruptions are linear in nature. However, real-world experiences show that they are not. Which is more disruptive to your day: 60 emails that each take a minute to deal with, or one 60-minute conference call? Pretty much everyone agrees that the answer is the 60 emails. It would be an interesting study to see how long a single disruption would have to be to equal an arbitrary number of minor disruptions, but it's going to exceed the time spent on the conference call. It can't be otherwise; that was proven in the 1700s. And remember, changing time zones has a cognitive cost.

"Driving up the transaction costs of conference calls and up-to-the-minute automated trading hardly sounds like a major loss to me."

And when you are elected Lord High Emperor of Humanity, this argument may have some smidgen of merit. I don't mean to be insulting; it's just that any argument that ends with "to me" is an argument from personal preference. Others have different preferences.

Why should YOUR preferences trump theirs? I get that this is your preference; the issue is that you wish to impose your preference on some 7.5 billion other people. It's reasonable to assume that they get an equal vote.

"I don't think cities should have a lot of say here and the lines should track solar noon."

That's not how it works, though. Demonstrably, political pull distorts these lines. You can see it on any map of time zones. The idea that this won't happen with the new division is simply not tenable. We live in a culture where which fast food restaurant you eat at is basted in part on politics; something as major as time zones is going to have every politician from the president to the county dog catcher weighing in.

You raise some good points about the linearity of disruptions that I had not considered. I I conceded the politics point to you, so I won't rehash that. Do recall that what I said is that this "would not be that big of a deal", which more formally is to say that there are costs and benefits to doing this and that the benefits (as shown in the paper) *could* be high and the costs are more manageable today than in the past.

But I do find your High Emperor characterization to be in bad faith. Of course I'm not trying to impose this policy by edict; I said "to me" because ALL arguments are made from the perspective of the person making them. I think it's a way to show humility and not pretend you are a God from on high who knows all by acknowledging you are a person (who can make mistakes.)

It's laughable that you would twist that into me desiring a personal dictatorship. That's the exact opposite of what I was saying.

The ~actual~ argument I made there is that this policy is a way of taxing some externalities. Feel free to address that if you'd like.

National television programing has always been oriented so that prime-time programs shown simultaneously in the eastern and central time zones are thus shown an hour later in the east than the central. Does this mean that residents of New Jersey generally stay up an hour later than those of Missouri to catch the evening news?

Now that we have smart phones and watches, I propose that they show us two times:

1) true local time, synchronized 12:00PM to solar noon at your exact location

2) global standard time

True local would be good for all local interactions (school and work start times, dentist appointments), and global would be good anything further away (national or international events, SOTU, World Cup) etc.

Before we run off and change the way the entire globe uses time, let's wait to see if this replicates.

It feels right to me, though checking, I see that Pacific Standard Time is only 5 minutes off Los Angeles solar time. So maybe no big deal.

Perhaps the real lesson here is we need better over the counter sleep aids than melatonin and Nytol.

Shifting the discussion a little from country to the entire planet. Call centers in the Philippines are 24/7/365. So are Las Vegas bars. A majority of those workers aren't living on their "biological" clock. You could even make the argument that anyone working before dawn (i.e. farmers) or after dusk (i.e. restaurant workers) aren't living according to their preferred biological rhythm.

This article was extremely interesting to read and was somewhat relatable from the standpoint of a college standpoint. Even though I have little knowledge on the subject, I was able to understand the statements and the points being made for this argument. What I liked best about this post was that it had information from very credible sources such as the Centers for Disease Control and Prevention and US Census.
Some of the information mentioned that I am a little familiar with is the circadian rhythm, which essentially is the rhythm or schedule in which a person usually sleeps. I learned a little about this rhythm in a former psychology class I had taken. We learned how in most cases the amount of sleep a person gets is related to how productive or efficient they are in their actions or thoughts.
In conclusion, this issue of irregular time zones in India sounds like it could be affecting more than people realize. It was even mentioned that if taken too far, disruption of this timing could have effects on health as well, such as obesity, diabetes, breast cancer, and cardiovascular diseases. This is not my area of expertise, but if I had to suggest any probable solution, I would suggest that we somehow using technology find a appropriate clock setting for the people in this time zone so that it would correctly align the biological time with standard time.

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