The north east of Scotland has a higher prevalence of Seasonal Affective Disorder (SAD) than the rest of the UK, a study has suggested.
SAD sufferers experience low moods, lethargy and anxiety
Consultant psychiatrist Dr John Eagles calculated that 3.5% of the area's residents suffered from the condition, compared to 2.4% in the rest of the UK.
He said scepticism about the condition among medics was slowly receding.
SAD stems from a lack of bright light and sufferers experience low moods, sleep problems and lethargy in winter.
Dr Eagles, of NHS Grampian, calculated that 3.5% of adults in the north east were affected by the most serious form of SAD, which can have a debilitating effect on sufferers.
He said that as his calculation was the only Scottish study of prevalence, the rate for the country as a whole was not known.
UK-wide studies have found that a further 10% of British adults experienced milder forms of SAD, sometimes known as the "winter blues".
The majority of sufferers are treated with a combination of anti-depressants and light therapy boxes, currently unavailable on the NHS.
Steve Hayes, managing director of Outside In, a Cambridge-based light therapy company, said that sales of the boxes were booming in the north east.
He explained: "Aberdeen and the surrounding area is a different story to the rest of the UK in terms of sales.
"It's a long way north, compared to the rest of the UK, and can get a lot darker there.
"Also, a significant proportion of the population seems to come from Texas and they can't believe what's hit them, after being used to blue skies."
Dr Richard Bowskill, consultant psychiatrist with the Priory hospital, said there was still some scepticism within the medical profession about whether the condition even existed.
"Psychiatrists are probably more accepting that it's a real condition, whereas some GPs are less open to making the diagnosis.
"It is sometimes difficult to differentiate between SAD and non-seasonal depression. There is often overlap between the two," he said.
However, Dr Eagles believes scepticism about the condition is gradually ebbing away.
He said: "Scepticism is probably slowly receding. It's not difficult to diagnose if you consider the possibility of SAD, but many doctors and sufferers don't consider it."
Neither CBI Scotland nor its UK counterpart had any data or anecdotal information about the number of employees with SAD, or the extent of lost productivity.
North Sea oil companies BP and Shell said they had not come across a significant prevalence among employees.
Dr Andrew Godge, medical adviser to the UK Oil Operators Association, said: "It isn't a big problem within the industry. That's not to say that I haven't come across it but it's no greater problem than elsewhere."
However, some UK employers have included light therapy as part of their occupational health policy.
Mr Hayes said his customers included government offices as well as individual sufferers.
He added: "In my experience, some SAD sufferers have actually lost their job over the winter; some have experienced relationship break-ups and children moving out of the family home.
"However, employers are increasingly sympathetic about the condition, mainly because doing something about it is pretty simple."