Mind Your Microbiome: Daylight Saving Time is Coming

What happens to your bacteria when you lose an hour of sleep?

We hate to remind you, but you’ll be getting an hour less sleep this coming Sunday (March 12th) if you live in the US or Canada.

Daylight Saving Time begins.

Oh dear.

Other countries start their Daylight Saving Time on differing dates, but here in the US, it always begins on the second Sunday in March.

Your Monday may therefore begin with less of a zing than normal (more on that in a second) but what impact, if any, does “springing forward” have on your bacteria?

We’ll soon find out.

First, however, spare a thought for trial defendants who may be due for sentencing on what has become known as Sleepy Monday.

Remarkable research led by the University of Washington last year showed that judges in the US are inclined to give defendants longer sentences the day after switching to Daylight Saving Time.

The researchers examined sentencing data collected between 1992 and 2003, discovering that sentences on Sleepy Monday were 5% longer than on other days.

They put this down to judges being sleep-deprived and, we might conclude, grumpier.

Could it have something to do with their gut microbiome, though?

Probably not, but unlike the judges themselves, whose alarm clocks will go off an hour earlier on Monday, surely the bacteria in the gut are on the go the whole time?

Well, curiously, no.

Although early microbiologists believed bacteria had no internal clocks, it’s now known that microbes do indeed operate on a circadian rhythm.

Circadian rhythms, by the way, are those that fluctuate on a cycle of around 24 hours – from the Latin circa (approximately) and “dies” (day).

The field of studying the relationships between time and living organisms is a relatively new science, known as chronobiology.

However, this fascinating field has roots dating back to the 18th century, when the snappily-named French astronomer Jean-Jacques d’Ortous de Mairan observed the daily movements of leaves on mimosa plants. He performed an experiment in which he subjected them to constant darkness, but he still found their leaves opening and closing in a daily rhythm.

de Mairan didn’t, however, reach the conclusion that plants have built-in clocks. Instead, he suggested that they were able to “Sense the Sun without ever seeing it.”

Speaking of darkness, there’s a lack of light down in your gut, of course.

See how cleverly we circled back around to your gut, just when you thought we’d strayed from the subject?

Since your microbiome has no access to illumination in order to set its rhythm, it pretty much relies on you, its host, to do this.

And a lot of its cues are provided by your eating pattern.

When the clocks go forward at 2 AM on Saturday night, you may not adjust immediately, using Sunday morning to kind of pick up the slack.

But on Monday, you’ll likely have to get up and running, whether you like it or not, so your gut microbes could find themselves awash in coffee, pop-tarts, or yesterday’s cold pizza (really?) an hour earlier than usual.

What you might call a rude awakening.

A lot of work on the microbiome’s circadian rhythm has involved investigations of mice at the Weizman Institute of Science in Israel.

Of course, unlike humans, mice are nocturnal. But in many other regards, their physiological responses can be uncannily human-like, making them useful for scientific purposes.

The researchers in Israel created the equivalent of jet-lagged mice by shifting the lights-on time in their cages forward by eight hours, keeping them like this for three days, then shifting them back again.

This process went on for four weeks, which was the equivalent of the mice flying back and forth between San Francisco and London for a whole month.

Just think of the miles they could have earned.

At the end of this period, the scientists saw that the mice began eating at random times.

Their gut microbes had stopped cycling normally, and the composition of microbial species started to change, too.

Fascinatingly, when the jet-lagged mice were fed a high-fat diet, they put on more weight than mice with normal rhythms, even when those other mice ate exactly the same amount of food.

In the normal mice, it was found that a startling 15% of bacterial species in the gut (amounting to 60% of its total microbes) varied in abundance during the day.

At night, a rodent’s microbes tend to switch on genes for growing, burning energy, and repairing DNA.

During the daytime, however, mice activate genes for getting rid of toxins and sensing their environment – more what you might call a maintenance mode.

Humans behave in the opposite way, with microbes supporting metabolism and growth activated during the day, and those responsible for maintenance operating at night.

So how did the scientists in Israel know that it was the gut microbes in the jet-lagged mice, rather than something else, that led to their increased tendency to put on weight while on the high-fat diet?

Well, when they transplanted gut bacteria from jet-lagged mice into germ-free rodents (creatures bred to have no microbiome, effectively), the transplant recipients also began putting on weight.

In a strange kind of way, therefore, their jet-lag was contagious.

Jet-lag, of course, usually only lasts a few days, but the scientists in Israel warned that gut dysbiosis (changes in microbial balance and composition) also occurs in shift workers, particularly those on variable shift patterns, potentially placing them at greater risk of glucose-intolerance and obesity.

As a matter of fact, uBiome is currently collaborating with researchers from Central Queensland University’s Appleton Institute in Adelaide, Australia, and the University of Chicago, to learn more about how shift workers’ disrupted sleep affects the composition of the human microbiome. The study will also examine whether this may in turn play a part in mental health problems and weight management issues.

Of course, it would be an exaggeration to suggest that putting the clocks forward an hour at the weekend will lead to you putting on weight, but it certainly won’t do you any harm to be mindful of waking your microbes earlier on Monday morning.

Be kind to them, and they’ll likely return the favor.

More reading

Biology of Time Change

Chronobiology: The Science of Time

Circadian Clocks in Microorganisms

Clocks in Bacteria V: How about E.coli?

Gut Microbes, Obesity, And The Circadian Rhythm

How Jetlag Disrupts The Ticks of Your Microbial Clock

Jean-Jacques d’Ortous de Mairan

Jet lag can cause obesity by disrupting the daily rhythms of gut microbes

Probing impact of sleep disruption on mental and physical well-being

Sleepy Punishers Are Harsh Punishers

Society for Research on Biological Rhythms

Switching to daylight saving time may lead to harsher legal sentences

Transkingdom Control of Microbiota Diurnal Oscillations Promotes Metabolic Homeostasis

Transkingdom Control of Microbiota Diurnal Oscillations Promotes Metabolic Homeostasis (paper)