Why does SAD exist at all

1
Why does SAD exist at all?

• Randolph Nesse
• The University of Michigan

2
Questions

• Why does seasonal affective disorder exist at
  all?
• Are seasonal mood changes useful?
• 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.
• Steady perky enthusiasm is just as abnormal as
  steady low mood (although more pleasant!)
• Is lower mood useful in the winter?

4
If seasonality is useful, then

• Most people should experience it
• Other organisms should show related effects
• Symptoms should be useful
• Timing of symptoms should be when useful
• More common in those with ancestors from northern
  latitudes

5
Many people experience seasonalityKasper, 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
• 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
• But their low mood is not useful now
• For them, bright lights are a bright idea

13
Conclusions

• Most people get a little low in winter
• It used to be useful, but isnt now
• 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.
• Bright lights are a bright idea!

14
Respect Mother Nature

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