A LOOK AT SEASONAL MOOD SWINGS and serotonin levels. “The molecular explanation to why these physical and emotional functions vary with seasonal changes has always been unknown, but the positron emission tomography (PET) technology used in this study was precise enough to detect correlations between dropping serotonin levels and amount of daily sun light. . . . The discovery of this correlation helps explain why more people experience major depressive episodes in the fall and winter than in the spring and summer. Major depressive disorder is the fourth leading cause of death and disability, according to the World Health Organization, and the goal of this research is to eventually prevent the illness itself. If researchers can label which specifics in certain environments raise or lower serotonin transporter levels, then they can suggest an ideal environment for people susceptible to seasonal depression, and hopefully prevent its onset all together.” Until then, you might want to schedule a Caribbean vacation, just to be safe!

UPDATE: Reader James Woolery, M.D., emails:

I noted your mention today of the connection between serotonin and changes in mood with a shortening of day length…

This time of year out my office window in the North Bay, looking over the estuaries of the Napa River, near evening I will see flocks of canvasback ducks wheeling in flight and settling on the water…

This phenomenon is exactly matched temporally with an increase in return visits of my depressed patients, and both phenomena derive, ultimately, from the same change: a decrease in the number of photons striking the retina, whether in man or bird.

Obviously, the solution is for us to fly south, too. Why am I not planning a Cayman trip?