Why does SADexist at all?
Randolph NesseRandolph Nesse
The University of MichiganThe University of Michigan
Questions
Why does seasonal affective disorder existat all?Why does seasonal affective disorder existat all?
Are seasonal mood changes useful?Are seasonal mood changes useful?
Is SAD a disease of the modernenvironment?Is SAD a disease of the modernenvironment?
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 assteady low mood (although more pleasant!)Steady perky enthusiasm is just as abnormal assteady low mood (although more pleasant!)
Is lower mood useful in the winter?Is lower mood useful in the winter?
If seasonality is useful, then…
Most people should experience itMost people should experience it
Other organisms should show related effectsOther organisms should show related effects
Symptoms should be usefulSymptoms should be useful
Timing of symptoms should be when usefulTiming of symptoms should be when useful
More common in those with ancestors fromnorthern latitudesMore common in those with ancestors fromnorthern latitudes
Many people experience seasonalityKasper, 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 observedNo big differences observed
Some tendency for more SAD in immigrantsto the NorthSome tendency for more SAD in immigrantsto 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 aremore normal because they are not decreasedby artificial lightSAD in those whose melatonin levels aremore normal because they are not decreasedby artificial light
But their low mood is not useful nowBut their low mood is not useful now
For them, bright lights are a bright ideaFor them, bright lights are a bright idea
Conclusions
Most people get a little low in winterMost people get a little low in winter
It used to be useful, but isn’t nowIt used to be useful, but isn’t now
Most of us are protected by artificial lightMost of us are protected by artificial light
People with SAD are less sensitive toartificial light and need much more of it tolive in artificial summer like the rest of us.People with SAD are less sensitive toartificial light and need much more of it tolive in artificial summer like the rest of us.
Bright lights are a bright idea!Bright lights are a bright idea!
Respect Mother Nature
Breast cancer is 5 times more common inmodern societiesBreast cancer is 5 times more common inmodern societies
Melatonin suppresses tumor growthMelatonin suppresses tumor growth
Women who work night shifts have a 50%increased risk of breast cancerWomen who work night shifts have a 50%increased risk of breast cancer
Women w/ more melatonin have less cancerWomen w/ more melatonin have less cancer
Women who sleep > 9h have 30% less riskWomen who sleep > 9h have 30% less risk
So use light IN THE DAYTIMESo use light IN THE DAYTIME