1. Why does SAD exist at all? Randolph Nesse The University of Michigan

2. Questions Why does seasonal affective disorder exist at all? Why does seasonal affective disorder exist at all? Are seasonal mood changes useful? Are seasonal mood changes useful? Is SAD a disease of the modern environment? Is SAD a disease of the modern environment?

3. Mood is useful Good to invest more when payoffs are large, save your effort when times are bad. Good to invest more when payoffs are large, save your effort when times are bad. Steady perky enthusiasm is just as abnormal as steady low mood (although more pleasant!) Steady perky enthusiasm is just as abnormal as steady low mood (although more pleasant!) Is lower mood useful in the winter? Is lower mood useful in the winter?

4. If seasonality is useful, then… Most people should experience it Most people should experience it Other organisms should show related effects Other organisms should show related effects Symptoms should be useful Symptoms should be useful Timing of symptoms should be when useful Timing of symptoms should be when useful More common in those with ancestors from northern latitudes More common in those with ancestors from northern latitudes

5. Many people experience seasonality Kasper, AGP, 1989 Slide By Norman Rosenthal

6. Slide by Thomas Wehr

7. More in the North (maybe) Rosen, PsyRes, 1990 Slide By Norman Rosenthal

8. Symptoms occur in winter (when useful?) Modell, Biological Psychiatry, 2005 Slide By Norman Rosenthal

9. Ethnic variations No big differences observed No big differences observed Some tendency for more SAD in immigrants to the North Some tendency for more SAD in immigrants to the North

10. A disease of modern times?

11. Wehr, AGP, 2001 Slide by Thomas Wehr

12. Most of us live in perpetual artificial summer! SAD in those whose melatonin levels are more normal because they are not decreased by artificial light SAD in those whose melatonin levels are more normal because they are not decreased by artificial light But their low mood is not useful now But their low mood is not useful now For them, bright lights are a bright idea For them, bright lights are a bright idea

13. Conclusions Most people get a little low in winter Most people get a little low in winter It used to be useful, but isn’t now It used to be useful, but isn’t now Most of us are protected by artificial light Most of us are protected by artificial light People with SAD are less sensitive to artificial light and need much more of it to live in artificial summer like the rest of us. People with SAD are less sensitive to artificial light and need much more of it to live in artificial summer like the rest of us. Bright lights are a bright idea! Bright lights are a bright idea!

14. Respect Mother Nature Breast cancer is 5 times more common in modern societies Breast cancer is 5 times more common in modern societies Melatonin suppresses tumor growth Melatonin suppresses tumor growth Women who work night shifts have a 50% increased risk of breast cancer Women who work night shifts have a 50% increased risk of breast cancer Women w/ more melatonin have less cancer Women w/ more melatonin have less cancer Women who sleep > 9h have 30% less risk Women who sleep > 9h have 30% less risk So use light IN THE DAYTIME So use light IN THE DAYTIME