Given that SAD is so tied to the seasons and to sunlight in
particular, you might predict that people who live in places
with cold, dark winters would be more likely than people living
in sunny climes to experience SAD. You'd be right. For example,
the rate of SAD in New Hampshire has been estimated at 10%,
whereas less than 2% of people living in Florida suffer with the
condition. In fact, I've known many patients over the years who
only developed SAD when they left places like Florida to live
further north. In this way, SAD is the quintessential
environmental disorder -- no winter, no SAD. But that is not the
whole story. Like all psychiatric conditions, SAD occurs at the
intersection of genes and environment, of nature and nurture.
This point has been brought home by several remarkable studies
showing that people in Iceland have remarkably low rates of SAD,
despite living in one of the darkest winter environments on
earth. Even more remarkably, people of Icelandic descent living
in the prairie provinces of