The days are getting shorter, and your mood might be too

It is early October, and the evenings are changing. Dinner happens in the dark now. The morning commute starts before the sun is fully up. For plenty of people this is the cozy season, sweaters and warm drinks and early nights. But for a lot of others, something quieter happens underneath: energy drops, sleep stretches longer, cravings shift toward heavier food, and motivation gets thinner week by week.

If that sounds like you, here is the first thing I want you to hear. You are not imagining it, and you are not weak for feeling it. There is a real pattern here, it has been studied for decades, and it has a name: major depressive disorder with a seasonal pattern, the condition most people still call seasonal affective disorder.

The pattern is specific. Low mood and low energy arrive in the fall or winter and lift in the spring or summer, year after year. That timing is the clue. A bad month is life. A bad season that returns on schedule is biology asking to be looked at.

Why would less daylight change your mood at all? Your brain uses morning light as its daily reset signal. Light tells your body clock when the day has started, which sets the timing for sleep, alertness, appetite, and the brain chemistry that keeps mood steady. When the days shorten, that signal gets weaker and arrives later. The clock drifts. Sleep gets heavier and harder to wake from. Energy and mood slide with it. This is not a character flaw. It is a timing problem in a very old system.

The encouraging part is that a timing problem can be addressed with timing. Morning bright light therapy, sitting near a bright light box for about thirty minutes after waking, is one of the best studied treatments in psychiatry for this pattern. A large meta analysis commissioned by the American Psychiatric Association reviewed the most rigorous trials and found that bright light therapy works for seasonal depression, with effects comparable to what antidepressant drug trials typically show. In other words, this is not a wellness trend. It is a treatment with real evidence.

One study tested the two approaches directly against each other. The trial enrolled 96 patients with winter depression across four Canadian centers and randomly assigned them to eight weeks of either morning light therapy or fluoxetine, a common antidepressant. Both groups responded at exactly the same rate, 67 percent, with nearly identical remission rates. The light group improved faster, showing an edge at week one, and had fewer adverse events like agitation, sleep disturbance, and palpitations. Same finish line, faster start, gentler ride for many people.

What does this look like in practice? A light box rated at 10,000 lux, used for about thirty minutes within an hour of waking, eyes open, the light off to the side rather than stared at directly. Consistency matters more than intensity. And if you already know October is when your slide begins, starting early in the season rather than waiting until you feel terrible is the smarter move. Many of my patients also keep a simple daily note, one line on sleep, one on mood, one on energy, because a pattern you can see on paper is much harder to dismiss or to miss.

A few cautions, because this matters. Light therapy is not for everyone. If you live with bipolar disorder, bright light can trigger mania or hypomania, so it should only be used with a clinician guiding the plan. Certain eye conditions and some medications that increase light sensitivity also call for a conversation first. And light therapy treats the depression, it does not replace a full evaluation. If low mood lasts most days for two weeks or more, starts affecting your work or relationships, changes your sleep or appetite in a big way, or brings thoughts of harming yourself, that deserves professional care promptly, whatever the season.

You do not have to wait until January to take this seriously. If every October feels like the start of a slow slide, that is not a coincidence to shrug at. It is data. And data is something we can work with. The light will come back in the spring either way. The question is whether you spend the dark months simply enduring them, or whether this is the year you do something about it.

Anthony

Sources: Golden RN et al., American Journal of Psychiatry (2005), meta analysis of 20 randomized controlled trials of light therapy for mood disorders, PMID 15800134. Lam RW et al., American Journal of Psychiatry (2006), randomized controlled trial of light therapy versus fluoxetine in winter seasonal affective disorder, PMID 16648320.