People who notice a mood shift in winter can mistakenly assume they have Seasonal Affective Disorder (SAD), a type of depression formally recognised in the 1980s, says Murray. SAD, however, is actually rare, affecting only about one in 300 Australians, he says.

A growing number of scientists also believe the influence of the seasons on mood has been overstated, more on which shortly. Depression, however, is not rare and can occur at any time of year. If you have been experiencing persistent low mood, take it seriously, be kind to yourself and seek support. Beyond Blue is a good place to start.

Early research into winter depression involved a great deal of excitement about sunlight and exposure to bright artificial light was shown to alleviate the symptoms. More recent research, however, has shown that more than half of people who experience winter SAD do not respond to bright light treatment. Furthermore, people who live in Iceland and the far north of Norway, where winter nights literally go on for months, have little experience of the disorder.

The way research into seasonal mood shifts has been conducted may also have led to exaggerated rates of prevalence, says Murray. Studies have typically asked participants to look back at their own past moods, which is notoriously unreliable. Some studies also asked leading questions, such as: "At what time of year do you feel worst?".

There are strong cultural associations with winter, says Murray, such as bare trees, grey skies and hibernation. "If you ask people 'at what time of year do you feel worst?', the risk is that they're not actually telling you how their mood varies with the seasons, they're just reporting on cultural associations with the seasons."