Ben Franklin almost got it right.
“Early to bed, early to rise, makes a man healthy, wealthy and wise” nailed sleep’s importance. But Ben’s folk wisdom apparently got good sleep’s cause and effect backward. New research shows that sleep quality depends on what you do the preceding morning.
The research, conducted at Rensselaer Polytechnic Institute and published in the June issue of the journal Sleep Health, finds that sleep quality is strongly affected by how much morning sunlight you get.
More than 100 government employees in five buildings across the US wore a Daysimeter pendant, a sensor that measures exposure to light frequencies unique to sunlight, for two weeks. The study found that workers who had significant morning sunlight exposure — whether through windows or directly — slept significantly better than workers who did not.
Versus workers who got little morning exposure to sunlight, the morning sunlight group fell asleep 27 minutes faster (spending just 18 minutes falling asleep versus 45 minutes — a lag called sleep latency) and got 19 minutes more sleep each night (355 minutes versus 336). The morning light group also did better on multiple other measures of sleep quality and had fewer symptoms of depression.
Run/walk in the sun
The new research sheds new light (sorry!) on 2014 research showing how sunlight multiplies exercise’s positive effect on sleep.
The study of 40 Korean men in their 20s found that exercising (walking or running) 30 minutes in the sun five days a week correlated with just 16 minutes of sleep latency, which beat both an exercise-only scenario (20 minutes sleep latency) and the no-exercise/ no-sun scenario (28 minutes).
Likewise, serum melatonin, the hormone that controls sleep, was significantly higher in the sun-exercise scenario (14.55 pg/ml) versus scenarios for only-exercise (12.8) and no-sun/no-exercise (9.45.) (It’s worth noting that, conversely, previous research showed that late-night exercise suppresses melatonin.)
Bottom line: if you want to sleep better, run in the morning sun.
a) The Korean research also examined an ‘only sunshine’ scenario, which improved sleep versus the no sun/no exercise model, but did worse than exercise with or without sun. Unfortunately, it’s hard to compare the two studies — the Korean group was significantly younger (which correlates with better sleep quality) and no information was provided about time-of-day for the sun-exercise test case.
b) Sunlight is an antidote to a variety of illnesses and disorders — ranging from cancer to diabetes to MS to ADHD to TB to bipolar disorder to myopia — so it’s no surprise that sunlight is important for sleep too. (Surprise fact: jetlag can trigger psychosis.)
c) Both studies are based on relatively small samples (~100 and 40 people respectively) with various tantalizing disjunctions in the findings. (What a pity the Korean study didn’t highlight when the run-in-the-sun occured! And we don’t get any granularity on whether any of the office-workers exercised!) The good news: when more of us are armed (or wristed) with wearables — particularly when UV sensors are added to motion, heart rate and sleep stage detection — the available data will exponentiate.
d) Too bad, as prescriptions for sleeping pills multiply, we’re not seeing ads promoting morning runs. As Richard A. Friedman, a professor of clinical psychiatry and the director of the psychopharmacology clinic at the Weill Cornell Medical College observes, you can’t patent light therapy and doctors receive scant training about sleep. (Worse, they’re trained to ignore their own need for sleep.)
Update: 1/06/18: New study linking poor sleep quality (duration, latency, varability) to rumination, a key component (some researchers think THE component) of anxiety and depression. Also worth considering studies showing that running significantly reduces rumination. Another study indicates even greater impact on depression from exercising outside.