Seasonal Affective Disorder (SAD) is a form of recurring depression or bipolar disorder that comes and goes at certain times of the year [1]. The most common form is the winter type, W-SAD, often referred to as “winter depression” or “winter blues.” In Austria, about 2.4% of people are affected by SAD, with the frequency increasing further north. [1] In Finland, 9.5% of the population meets the criteria for winter SAD, and 18.5% for a sub-syndromal form of it. [2] In a survey in Germany, slightly less than one-third of respondents reported experiencing impaired mood during the winter period [3].

SAD is associated with a delayed circadian phase. People with delayed sleep phase syndrome (DSPS) are 3.3 times more likely to develop SAD [1]. The severity correlates with the extent of the delay.

Bright Light Therapy

Bright light therapy (BLT) is the first-line treatment for seasonal affective disorder. The recommended setup is exposure to 7,000-10,000 lux of broad-spectrum white light for 30 minutes each morning for at least two weeks. If natural daylight is unavailable, the typical light source is a daylight lamp, but light therapy glasses are an emerging alternative. The exact timing depends on individual chronotype and should be determined in consultation with a doctor. BLT can improve SAD symptoms within just a few days and is most effective when done consistently at the same time each day [5].

Light is believed to positively affect mood through two pathways:

1. Consistent exposure stabilizes and strengthens the circadian rhythm. Synchronizing the circadian clock with an external schedule seems beneficial, as morning BLT has been shown to be more effective than BLT at other times of the day [5].
2. Light modulates the availability of serotonin and other monoamines, which are critical factors in affective disorders and sleep regulation [5]. The exact mechanisms behind BLT are still an active area of research.

Dawn Simulation

Artificial dawn simulation has also been shown to be an effective countermeasure against SAD. Dawn simulation begins about 90 minutes before the scheduled wake-up time with a very low intensity (0.001 lux) and then gradually increases to a maximum of ~300 lux by the planned wake time [5]. In one study, dawn simulation improved SAD symptoms by 49.5%, while BLT improved symptoms by 57.1% [6]. Since many people find it difficult to adhere to a prescribed morning BLT schedule [7], dawn simulation could be an attractive alternative.

The caveat here is that the light sources used in the studies had a diffuse, wide illumination range that provided adequate lighting regardless of the sleep position. This is not the case with commercial wake-up lights, which have a smaller light field. Therefore, dawn simulation with commercial wake-up lights is not officially recommended as a treatment for SAD [5].

Conclusion

The lack of sunlight in winter can pose a serious threat to mood. Winter depression seem to be associated with a delayed circadian phase. Morning light applications have the potential to cure or alleviate seasonal affective states. They come in the form of bright light therapy as the first-line treatment and dawn simulation as a possible alternative.

If you find that you are suffering from winter depression (SAD), please seek professional medical help. If you’re planning to incorporate light therapy into your morning routine, check out our articles on daylight lamps for guidance on selecting suitable devices.