Dose of summer sun good for you - and others

by the Canadian Institutes of Health Research

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Research Profile - July 2007

Feeling quarrelsome and irritable? Try chilling-out with a little sun. That's the conclusion of a new Canadian study that's the first to show an association between catching rays and not just improved mood but also being more sociable.

And while Canadians are known to seek-out the sun in winter, the new study also reveals that getting a good dose of bright light in the summer is equally as potent a mood and behaviour booster.

"We found that when a person is exposed to more bright light during part of the day, whether it's in the winter or summer, they're more likely to be agreeable during that part of the day than when they're exposed to less bright light," says Simon Young, a research psychiatrist at McGill University in Montreal.

The study led by former PhD student Marije aan de Rot and funded by the Canadian Institutes of Health Research, involved 42 Montreal-based indoor workers. They wore light meters to record their light exposure minute-by-minute for several weeks. The participants also recorded their moods and social interaction at intervals in the morning, afternoon and evening.

As little as 20 minutes exposure to bright light in winter - when many Canadians experience the effects of the low-light winter blahs, formally called Seasonally Affective Disorder (SAD) - made participants not just happier, but by their own estimation also more pleasant to be with.

In the summer, the average participant received only one-and-a-half hours of bright light per day. Dr. Young notes that this is probably less than our ancestors would have received on a winters' day while working outside.

"Compared with the situations under which humans have evolved we're living in a very light-deprived world," Dr. Young says.

Indoor artificial lighting in offices is not usually bright enough to stimulate the effects of sunlight, he says.

While Dr. Young notes that the results are preliminary, he's pursuing the link between bright light and changes in brain chemistry. His research points to a link between bright light and a boost in serotonin, low levels of which are closely associated with depression.