Winter Depression and Lack of Light: When the Dark Season Weighs on Your Mood

In 1984, a team led by Norman Rosenthal at the US National Institute of Mental Health described for the first time 29 people whose depressions returned at the same time every year. Striking features were a lot of sleep, overeating and carbohydrate cravings. In eleven of them, initial trials suggested that extending the day with bright artificial light might have an antidepressant effect.

One detail is often overlooked: most of these first people had bipolar disorder, mainly type II. We will come back to this in the section on safety.

A review from Athabasca University in Canada summarized the state of knowledge in 2015. According to it, those affected more often are women, younger people, people living far from the equator, and people with depression, bipolar disorder or SAD in the family.

The review describes the milder form, the winter blues, as a separate, subthreshold picture. For you this means: not every winter low is depression, but every recurring low deserves a closer look.

Between 1999 and 2003, a research team led by Nicole Praschak-Rieder in Toronto examined the brains of 88 healthy people with an imaging method, PET. In autumn and winter, serotonin transporter binding was higher in all brain regions examined than in spring and summer, and the fewer the hours of sunshine, the higher the values.

The transporter is like a vacuum cleaner that pulls serotonin back out of the gap between nerve cells. More vacuum cleaners could mean that less serotonin remains for signal transmission in the dark half of the year. This is a mechanism seen in healthy people, not proof of the cause of winter depression, but a very plausible bridge.

In 2001, Thomas Wehr and colleagues at the National Institute of Mental Health measured melatonin over 24 hours in 55 people with winter depression and 55 healthy controls, in winter and in summer. In those affected, the nightly melatonin phase lasted longer in winter than in summer, on average 9.0 versus 8.4 hours, while in healthy people it stayed the same.

Animals use exactly this signal to adapt their behavior to the season. The authors themselves stress that this does not prove causality. But it fits the idea that some people respond to winter more strongly with a biological withdrawal program.

In 2006, Alfred Lewy and his team at Oregon Health and Science University tested whether a shifted body clock is linked to the severity of winter depression. They found a time window in which good alignment of circadian rhythms went along with lower depression scores.

For you this means: in many people affected, the body clock seems to run behind the calendar in winter. Morning light could pull it forward again, and this is considered one possible way light therapy works.

In 2001, a team from Taipei and Vancouver compared the blood of 15 people with winter depression with that of 15 healthy people of the same age and sex. In those affected, the inflammatory messenger interleukin-6 was markedly elevated. After two weeks of light therapy, mood improved in all 14 people who completed the study, but the inflammatory markers stayed unchanged.

This is a small study, and it teaches two things. The immune system might play a part in winter depression. And light seems to influence mood through other pathways than a rapid lowering of these markers.

In 2005, Robert Golden and colleagues at the University of North Carolina analyzed all randomized trials of light therapy for mood disorders that met strict criteria. Bright light for winter depression showed an effect size of 0.84 across eight studies, and dawn simulation 0.73 across five studies.

The authors write that these effects were comparable in size to those of most antidepressant trials. At the same time, only 13 percent of the studies found met the quality criteria. That is an honest mix of hope and caution.

In 2020, Edda Pjrek and her team at the Medical University of Vienna pooled nineteen randomized trials comparing bright light with placebo light. Light therapy did better on depression scores, and the likelihood of responding to treatment was 42 percent higher.

The authors regard light therapy as an effective treatment for winter depression, but criticize small studies and a moderate to high risk of bias. For you this means: a solid component that deserves larger studies.

Raymond Lam and his team ran the Can-SAD study at four Canadian centers over three winters. 96 people received either 30 minutes of 10,000 lux light in the morning plus a placebo capsule, or dim placebo light plus the antidepressant fluoxetine. In both groups 67 percent responded, and 50 and 54 percent reached remission.

Light showed a slightly faster effect after one week, fluoxetine somewhat more often caused agitation, sleep problems and palpitations, and both were well tolerated overall. The authors recommend also taking the preferences of those affected into account. Light and medication stand on equal footing here.

In 2015, Kelly Rohan and her team at the University of Vermont compared six weeks of a specially adapted cognitive behavioral therapy, CBT-SAD for short, with six weeks of light therapy in 177 adults with winter depression. Both groups improved markedly and comparably, with remission rates of 47.6 and 47.2 percent.

The authors conclude that both are viable treatment options. For you this means: you have more than one well-studied path.

The same team followed these people over the next two winters. In the first follow-up winter, the groups did not differ. In the second winter, 27.3 percent relapsed after behavioral therapy, and 45.6 percent after light therapy.

One possible explanation: light might mainly have an effect for as long as you use it, while strategies learned in therapy can last. That is a strong argument for seriously considering psychotherapy in recurring winter depression.

In 2019, a Cochrane team led by Gerald Gartlehner analyzed studies in which antidepressants were meant to prevent a new episode of winter depression. For extended-release bupropion, three trials with 1,100 people showed a 44 percent lower risk of relapse, with moderate quality of evidence.

At the same time, headaches, sleep problems and nausea occurred more often, and even in a high-risk group three out of four people did not benefit. The authors advise discussing benefits and drawbacks openly. That is exactly how I see it too.

In 2018, a team led by Dorothy Sit at Northwestern University studied people with bipolar depression who were already being treated stably with mood-stabilizing medication. Bright light at midday led to remission more often than placebo light over six weeks, namely in 68.2 versus 22.2 percent, and no switches into mania were observed in this study.

However, people with rapid cycling or mixed symptoms were excluded, and everyone was on medication and under close monitoring. For you this means: light can be a component in bipolar disorder too, but only under psychiatric supervision and not as a self-experiment.

In the US VITAL-DEP trial, more than 18,000 adults aged 50 and over received either vitamin D3 or placebo for an average of 5.3 years. The risk of developing depression or clinically relevant depressive symptoms did not differ between the groups.

The authors therefore see no basis for using vitamin D3 to prevent depression in adults of this age. However, this concerned people without depression at the outset and did not specifically target people with a deficiency.

In 2020, a team from Taiwan pooled twenty-five randomized trials on vitamin D and negative emotions. Overall there was an effect, especially in people with diagnosed depression and with a vitamin D level of 50 nmol/l or less.

The studies were very different from one another, however, and the authors themselves urge caution. For you this means: a measured deficiency deserves to be corrected, but vitamin D is not a substitute for light, therapy or medication.

In 2019, a Cochrane team led by Barbara Nussbaumer-Streit at Danube University Krems screened more than 3,700 records on preventive light therapy. Only one single small study with 46 people met the criteria, and its results were too uncertain for a clear conclusion.

For you this does not mean that light is useless for prevention. It means we simply do not know for sure yet. The authors advise basing the decision strongly on the preferences of those affected.