A flurry of newspaper headlines have called into question the existence of SAD, or Seasonal Affective Disorder. Scientists, they reported, appear to have debunked a widespread conviction, that feeling low in winter time is a genuine illness caused by disturbed levels of brain chemicals and that demands treatment.
A visit to any number of Seasonal Affective Disorder (SAD) websites leads to online questionnaires offering “diagnosis”, treatment recommendations, and advertisements for light boxes – gadgets that simulate daylight and compensate for poor exposure to the real thing. SAD is identified as a form of depression caused by disturbances of hormonal rhythms sensitive to daylight, primarily melatonin. Unusually, intense exposure to artificial light often is advocated as a treatment. There is even a device that can be worn on the head, allowing the patient to use a light box on the move.
Where’s the evidence?
The publication prompting the news story is a large US survey associating the experience of depression with season, latitude and sunlight exposure. Although various models confirm associations between the experience of depression and variables such as age, gender, education, employment and marital status, it found there were no associations between depression and season, latitude, a combination of the two, or sunlight exposure – as derived from knowledge of the respondent’s location and US Naval Observatory records.
These are high-quality data that have been analysed appropriately. They also confirm similar findings that are equally unable to associate reported mental distress and fluctuations in daylight length, even those of the extreme type found in polar regions.
The sad truth
So how might we reconcile the fact that seemingly conclusive research is unable to demonstrate an association between symptoms of depression and sunlight exposure, with the sheer number of people who believe they suffer from SAD?
According to one source, SAD prevalence ranges from 9.7% in New Hampshire to 1.4% in Florida. In the UK, the estimate is that it affects 2.4% of the adult population. These estimates represent a large number of people – and their conviction that they are suffering from a real illness is often a strong one.
Indeed, SAD can even carry the juridical significance of a formal disability. According to the Los Angeles Times: “The US 7th Circuit Court of Appeals in Chicago ruled in October  that a teacher could pursue a lawsuit against her former employer alleging that the school district had failed to accommodate her SAD, causing her mental health to deteriorate.”