There are people who become more depressed during autumn and winter. It is called Seasonally Affective Disorder or SAD for short. For example a study in Norway found modest increases in levels of depression between November and March among 10,000 men and women (Oyane 2008). As an ecotherapist I am interested in understanding what is going on here and whether ecotherapy can play a part in alleviating the symptoms of depression in winter. Does SAD really happen? What are the processes that might influence a seasonal change in mood? And can we counteract the negative effects of seasonal change by using ecotherapy?

In 1984 American psychiatrists began to notice patients who showed a history of recurrent depression which developed in autumn and winter and then abated during spring and summer (Rosenthal 1984 in Golden 2005). It was already known that reduced light exposure lead to increased melatonin in the body and the assumption was that melatonin somehow had a depressive effect on the mind. The researchers carried out preliminary trials to see if exposing seasonally depressed individuals to bright light (with similar wavelengths to natural light) as opposed to dim light would delay the onset of SAD.

Soon after the publication of these results, which were positive in their outcome, it was possible to buy a Light Therapy box containing special light bulbs that mimicked daylight. People were encouraged to sit in front of the natural light box for set periods every day in order to reduce their SAD. Much research into the effectiveness of Light Therapy ensued, but the conservatism of mainstream psychiatry to all things non-pharmacological meant that it was not universally adopted. In 2003 the American Psychiatric Association decided to review the efficacy of light therapy in the treatment of mood disorders.

The meta-review laid down strict research criteria such as the use of randomised controlled trials and effective placebo conditions (Golden 2005). Most of the studies were flawed according to their criteria and only 13% were accepted for the review. However the twenty studies that made it to the finals indicated some interesting conclusions. The results from the selected research revealed a significant reduction in depression symptom severity with bright light treatment for both SAD, dawn simulation (light intensity is gradually increased over 1.5 to 2 hours) and non-seasonal depression. The authors add a word of caution with regard to two issues they did not address. One is safety, no one knows yet the effect of this treatment on the eye, and the combined effects of medication and high light exposure. Secondly only adults were tested; different concerns arise when using this therapy with children and older adults.

With further research the picture seems more complex, although the overall link between sunlight and mood change holds up. There could be cultural, genetic and climatic factors at play. For example the incidence of SAD in the USA is twice that of Europe, even though Europe is in a higher latitude (Mersch and others 1999 in McNair 2012). There are positive correlation links between cloudiness and SAD as well as minutes of sunshine, day length and temperature (Potkin and others 1986 in McNair 2012). A study of Icelandic immigrants in Canada suggests there may be a genetic adaptation which conferred the immigrants with lower rates of SAD than among other Canadians (McNair 2012).

If we look at birds and animals we can see countless examples of changes in their behaviour as a result of daily and seasonal changes, what are called circadian rhythms. Reproductive hormones become active in all our native species of birds not long after the midwinter solstice, and by Valentine’s Day many of our common woodland birds are already paired up and ready to breed. The trigger for the change in behaviour is daylight. A rise in temperature does have an effect on breeding behaviour but is an unreliable signal for seasonal change. Anyone familiar with the British weather will know what I am talking about! However daylight consistently gets stronger and the days lengthen from the beginning of the new year, thus providing the body with a reliable indicator of seasonal change. Light fluctuations tell our bodies about diurnal cycles as well as seasonal changes. Melatonin is the hormone involved in circadian and seasonal rhythms. It appeared early in evolution and is found in plants and animals. In humans melatonin is produced by the pineal gland situated deep below the brain but neurally independent of it. As light decreases one effect is that our body produces more melatonin, triggering a desire to sleep. As an aside, in older people melatonin production comes into play earlier and peaks earlier in the night, while for adolescents the reverse is true, which explains a lot about both groups of people’s behaviour.

Research shows (McNair 2012) that older people sleep much better if they are exposed to bright light during the day, particularly first thing in the morning (light is also bluer at that time of day). Unlike vitamin D production the light only has to reach the eye to have this effect and so even overcast days are effective. Much more light reaches the eye when we are outdoors than if we are even close to a big window.

Blue light is the most reactive wavelength for the suppression of melatonin. The open fires our ancestors sat around, and incandescent bulbs we used to use, produce much less blue and more orange light. Modern LED, fluorescent lights and computer screens are cooler and bluer in tone. Harvard Medical School (Harvard Medical School 2013) recommends we should expose ourselves to lots of bright light during the day in order to help us sleep better at night and to boost our mood during the day. They also recommend not using computer screens 2-3 hours before going to sleep.

Researchers in Sweden found that if people working in offices are exposed to blue enriched white light then their alertness, positive mood, concentration, and daytime sleepiness were significantly improved (Viola AU and others 2008). They also slept better at night. There is some suggestion that their alertness, concentration, and performance may have been affected by participant’s expectations though.

If blue light wavelengths are the most effective in suppressing melatonin and consequently boosting our mood I am also wondering if the pleasure we get from seeing blue sky is in part related to this effect. Studies of people’s preferences when looking at photographs of nature show that a blue sky is significant (Pretty & others 2005).

In conclusion, the results from research suggest that doing ecotherapy on a sunny day, particularly in winter, is likely to boost a person’s mood and reduce anxiety.

What about Spring suicides?

Is there evidence that there are more suicides in Spring than any other time of year? If so how are they explained?

Does a lack of vitamin D, which we get from the sun, affect the mind?

To find out the answers to these questions and other environmental effects on mental health you will have to wait for my new book: With Nature in Mind: an ecotherapy manual for mental health professionals, to be published by Jessica Kingsley in the UK and USA in April 2016.