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Why does SAD exist at all?

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.

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Why does SAD exist at all?

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  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 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!

  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 > 9h have 30% less risk • So use light IN THE DAYTIME

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