It’s that time of year – the clocks have gone back, it’s cold, and already getting dark on our commute home. Whilst many people moan about this time of year, for some it can trigger symptoms of low mood and depression.
Seasonal Affective Disorder is defined as “a type of depression that comes and goes in a seasonal pattern.” (NHS Choices). It’s typically worse from December to February, getting better in spring and summer. For SAD to be diagnosed, there has to be clear evidence of worsening symptoms during winter, which can’t be explained by other circumstances (DSM-IV). In addition, there needs to be evidence for part or full remission during the summer months. Symptoms of SAD are similar to those of depression: low motivation and self-esteem, sleep problems, changes in appetite, withdrawing from social interactions and persistent negative thoughts.
Estimates of the prevalence of SAD range from 0 – 9.4% of the population, depending on who is being studied (Magnusson, 2000). One study compared rates of SAD at 4 different latitudes in the USA and found that is was most common in the northern latitudes (Rosen et al, 1990), which would be expected as SAD can be triggered by lower levels of natural light. This study also found higher rates of SAD in females than males (this finding is in line with overall levels of depression between men and women). It is thought to be caused by the lack of sunlight in winter months disrupting our circadian rhythm, which can be described as our internal body clock. This can affect the serotonin system in the brain, which is responsible in part for mood regulation.
There are various different treatment options for SAD, including light therapy, cognitive behavioural therapy, or antidepressants (Lurie et al, 2006). I’ve spoken about CBT before on this blog (see here for more information), so today I’ll just focus on light therapy and antidepressants as treatments for SAD.
Light therapy involves sitting by a specialised lamp, which emits a specified wavelength and brightness of light (at least 2500 lux). It is thought to work by encouraging the brain to produce serotonin – a neurotransmitter which is linked to feeling happy. Sitting by a lamp for 30 minutes to an hour each morning is the recommended ‘dose’ of light (NHS.uk). One meta-analysis has shown that light therapy is as effective as drug therapy in treating SAD (Golden et al, 2005).
Some antidepressants also work by increasing our serotonin levels. Known as SSRIs (selective serotonin reuptake inhibitors), they work by stopping as much serotonin from being reabsorbed at synapses in the brain and therefore leading to an increase in our mood. For antidepressants to be optimally effective in SAD, the NHS recommend starting to take them before winter and continue until spring.