Scientific studies have shown that sunlight encourages the production of serotonin in our brains, writes Muiris Houston
Some very delicate frames indeed may be affected by wet weather -Samuel Johnson 1763
THE POOR weather has been a regular "ice-breaker" in consultations over the past number of weeks. With extensive flooding at times, there has been no shortage of reference points, either local or international.
Of course, there has been the inevitable gnashing of teeth about the summer being over without it having delivered a reasonable quota of sunshine. One patient told me that it had been a full eight days since he had seen even a glimpse of blue sky.
But it is not as notable in practice as one August some years ago which stands out for its weather-related consultations.
It too was a bad summer - not as much rain as this year but it was cold, windy and cloudy. In about the third week of August, it all became too much, at least for some of my patients.
It was the first and only time when a number of people came to the practice complaining of "feeling down" because of the weather. Their mood had dipped appreciably, although most would not have been classified as clinically depressed.
Rather they were lethargic, de-motivated and simply could not face the prospect of "summer" merging into winter. And perhaps most notably, they all came to see me over the same 10-day period.
I remember at the time musing about a scientific link between weather patterns and neurotransmitters in the brain; however, with no science to back the theory up, the episode got filed away in the "life's curiosities" department of my memory.
Until last week, that is, when a paper in the medical journal Archives of General Psychiatrycaught my eye.
The Canadian authors carried out brain scans at different times of the year on some 90 healthy people. From these, they calculated the levels of a protein responsible for transporting the brain chemical serotonin.
The results show that serotonin levels were high in spring and summer and lower in winter and autumn. But of particular note was the finding that brain serotonin levels were lowest on days when meteorological data reported the least sunshine.
Serotonin is a key chemical controlling mood in the brain. Low levels have been linked with depression: the main class of antidepressant therapy used by doctors is called selective serotonin reuptake inhibitors (SSRIs).
The psychiatrists from the University of Toronto, Canada said: "These findings have important implications for understanding seasonal mood change in healthy individuals, vulnerability to seasonal affective disorder, and the relationship of light exposure to mood", adding that future research should focus on temperature and humidity as well as sunshine levels.
Certainly, the research goes some way to explaining seasonal affective disorder (Sad). The depression accompanying long winter nights, although recognised as a disorder in its own right, has never been fully explained.
Despite a relatively recent resurgence, Sad is not a new disease. In the second century, Aretaeus noted that "lethargics are to be laid in the light and exposed to the rays of the sun (for the disease is gloom)".
Most recently, researchers have suggested that Sad sufferers may be closer to their mammalian roots than others: mammals use changes in the length of the day to regulate seasonal behaviours.
Like mammals, Sad patients have been shown to secrete greater amounts of the chemical melatonin in winter, compared with during summer months.
In his book Flagging the Problem: a new approach to mental health, Drogheda GP and occasional Irish Timescolumnist Dr Harry Barry notes that melatonin and serotonin are interwoven into the normal circadian rhythms of our lives. Darkness encourages the brain to produce melatonin. Light increases the production of serotonin. "Sad seems to be caused by an excessive production of [melatonin] and in particular, a lack of serotonin," he says.
Another factor pointing to a role for sunlight in mood regulation is the finding that the incidence of Sad increases as one moves northwards.
The condition is said to be unknown in those who are living within 30 degrees of the equator.
And as my clinical experience shows, certain meteorological conditions can trigger Sad - like symptoms in those without a history of mood disorder.
• Dr Houston is pleased to hear from readers at mhouston@irish-times.ie but regrets he is unable to reply to individual medical queries