Why Your Body Notices Fall Before You Do

Autumn officially started on September 22. You probably didn't notice. Your brain did.

A cluster of about 20,000 nerve cells, sitting just above the point where your optic nerves cross, reads the light that reaches your eyes every day and uses it to set the clock for the rest of your body. That light is changing faster right now than at any other point in the year, and your body is already adjusting, whether or not you've put the shorts away.

If you've been hitting snooze more, wanting dinner at 5:30, or eyeing the bed at 8:45, that's probably not laziness. It's October.

The days are shrinking fastest right now

Day length barely moves near the solstices and changes quickest around the equinoxes. New York gets roughly 11 hours and 45 minutes of daylight on October 1 and about 10 hours and 30 minutes by Halloween. That's more than an hour gone in a month, and more the farther north you live.

The later sunrise matters most. Morning light is the strongest signal your internal clock gets, and once sunrise slides past your alarm, you start the day in the dark.

Some bodies take the memo harder

Here's the detail we find most interesting. In a 2001 study from the National Institute of Mental Health, people with seasonal affective disorder released melatonin, the hormone that tells your body it's night, for about 36 minutes longer each night in winter than in summer. In the comparison group it barely changed. The researchers likened it to the seasonal signal other mammals use to get ready for winter.

So everyone's clock sees the shorter days, and some bodies respond far more than others. Harvard Health's explainer on winter depression lays out the chain: less light, more melatonin, less serotonin. The Sleep Foundation adds a second piece. Your internal clock drifts later in winter while your alarm stays put, so you end up a little jet-lagged without leaving your time zone.

The blues, or something more

A little seasonal drag is normal. Seasonal affective disorder is different. It's a form of depression that returns each fall and winter, and it affects about 5% of Americans. If last winter brought hopelessness, lost interest in things you usually love, or real trouble getting through the day, talk to a doctor now. The Sleep Foundation suggests that people with a known pattern start light therapy two to four weeks before symptoms usually show up, which for many people is this month. The standard setup is a 10,000 lux light box for about 30 minutes before 10 a.m.

An October plan, one week at a time

For everyone in the "just a bit more tired" camp, timing does most of the work. Add one change a week.

Week one: Hold your wake time. Sunrise is moving. Your alarm shouldn't, weekends included. If you do need to shift it, our circadian rhythm guide suggests 15 minutes at a time.

Week two: Get outside within an hour of waking. Even a gray morning is many times brighter than your kitchen. Coffee on the porch counts. So does walking the dog.

Week three: Let the cold do the alarm clock's job. When it's still dark at 7 a.m., a short plunge is a reliable way to feel awake. Cold water sets off a fast release of norepinephrine, a chemical messenger tied to alertness. In one well-known study, an hour at 57°F raised it by about 530%. You won't be in for an hour, but you'll feel it. Start around 55 to 60°F for a minute or two. If you have a Plunge, set the temperature in the app the night before so it's ready when you are, and pair the plunge with daylight, since light is still what sets your clock.

Week four: Move the heat earlier. A warm session in the evening helps many people sleep because the body cools off afterward, and that drop is one of the cues for sleep. A 2019 review found that a warm bath or shower one to two hours before bed helped people fall asleep about 10 minutes faster. Our natural sleep aids guide covers fitting a sauna session into your evening. Then keep the bedroom cool, around 60 to 67°F, and dark.

Before you start

If you have a heart condition or high blood pressure, or you're pregnant, check with your doctor first. Our ice bath do's and don'ts covers the rest. And if the season ever brings thoughts of harming yourself, call or text 988 to reach the Suicide and Crisis Lifeline.

Tomorrow morning

Look up tomorrow's sunrise time and compare it with your alarm. If the alarm wins, take your coffee outside for ten minutes once the sun is up. That's the whole assignment.

Sources

• Harvard Health Publishing, "Shining a light on winter depression"
• Sleep Foundation, "Seasonal Affective Disorder: Sleep Tips to Beat the Winter Blues"
• Plunge, "What Is the Circadian Rhythm? And How to Fix It"
• Plunge, "Natural Sleep Aids: 9 Methods to Sleep Better"
• Wehr et al., Archives of General Psychiatry, 2001
• Haghayegh et al., Sleep Medicine Reviews, 2019