Brightening Up Winter: Shedding Light on Beating the Seasonal Blues

Do you miss the sun in winter and can’t wait to feel the sun on your skin again? If you answer ‘Yes’, then don’t worry – you are not the only one.

But some people feel depression-like symptoms from the start of early winter till the beginning of spring[1]. What is known to most people as ‘winter blues’ or ‘seasonal depression’ is actually called seasonal affective disorder (SAD). Alone in 2023, 280 million people  around the world suffered from depressive symptoms, making it the most common mental disorder. In the United States SAD affects 11 million people and even 25 million have a milder form (‘winter blues’) [1]. The cause of this disorder is not known, but there are two explanatory approaches. One explains the symptoms with a delayed circadian rhythm and the other with a different uptake of serotonin (neurotransmitter, regulating e.g. mood). For both of these hypotheses, treatment with light therapy (LT) seems to relieve the symptoms [3]. To prevent SAD, doctors recommend going outside, exercising, eating a balanced diet, and keeping up social contact [1].

Light therapy is a common and effective treatment for SAD and has been used for over 40 years. During LT sessions, patients are exposed to a light box with 10,000 lux of light for about 20 to 30 minutes, usually in the morning [4]. While the exact mechanism behind LT remains unclear, it is believed to simulate natural sunlight to help regulate internal circadian rhythms and neurotransmitter levels[5,6]. Reviews and meta-analyses have shown the efficacy of LT for SAD. A significant improvement for patients treated with LT against people not treated was found in a network meta-analysis in 2024: they analysed 21 studies and 1037 patients, comparing pharmacological and non-pharmacological intervention treatments [7].Another meta-analysis in 2020 found that LT was superior to placebo, highlighting LT as a highly effective and preferred treatment option for individuals with SAD [8].

Light therapy has shown effective results in relieving symptoms of SAD. The key parameters for LT include intensity, wavelength, exposure duration, and timing of light exposure during the day. This study also showed that there was no significant difference in efficacy between morning, afternoon, and evening treatments [9]. However, there were also some studies suggesting that LT was more effective in the morning [10]. This difference may be related to the use of different light intensities and exposure times, but there is no accurate conclusion yet. As for the effect of wavelength on LT, although there was a hypothesis that blue light may be more effective, experiments have not supported this notion[11].

There is a discrepancy in opinions in the field which is reflected in the published papers. While several studies confirmed that LT works to relieve depressive symptoms [12,13,14,15],  there are other more critical voices [8,9,16,17,18]. The main critique points are the duration of the trials, the sample sizes, and the lack of standardization of the light therapy parameters [16,17]. Where one study shows an antidepressant effect beyond placebo after three weeks [13], a meta-analysis on adolescents revealed an effect of LT better than a placebo control group in only two studies [16].

Whether light therapy is an effective treatment for patients with SAD or the reliving of symptoms could be explained by other therapeutic variables unrelated to light (e.g. improvement in day-night structure, or recognition of complaints) [11], the psychological field seems to be in disagreement. But since LT is well-tolerated with patients [17] and ensures high safety [19], it still is a normal practice. What every researcher could agree on was that there is a need for ”(...) adequately controlled clinical trials of LT treatment protocols” [16]to establish efficient and accepted treatment strategies. For this moment one thing seems to be of importance – no harm is done!

Min Mao, Sophie Merz, Arezou Aminizadeh, Niloofar Norooziheris, Abiyamol Joy

Issue 27