Transcript SAD - University of Michigan Depression Center

Why does SAD
exist at all?
Randolph Nesse
The University of Michigan
Questions
Why does seasonal affective disorder exist
at all?
 Are seasonal mood changes useful?
 Is SAD a disease of the modern
environment?

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?

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

Many people experience seasonality
Kasper, AGP, 1989
Slide By
Norman Rosenthal
Slide by Thomas Wehr
More in the North (maybe)
Rosen, PsyRes, 1990
Slide By
Norman Rosenthal
Symptoms occur in winter (when useful?)
Modell, Biological Psychiatry, 2005
Slide By
Norman Rosenthal
Ethnic variations
No big differences observed
 Some tendency for more SAD in immigrants
to the North

A disease of modern times?
Wehr, AGP, 2001
Slide by Thomas Wehr
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

Conclusions
Most people get a little low in winter
 It used to be useful, but isn’t 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!

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 > 9h have 30% less risk
 So use light IN THE DAYTIME
