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Increased heart attacks in the winter may be due to lack of sunshine – Nov 2012

Seasonal Variation in Cardiac Death Rates is Uniform across Different Climates

American Heart Association conference presentation,Nov 07, 2012,
Bryan G Schwartz, Robert A Kloner, Good Samaritan Hosp, Los Angeles, CA

BACKGROUND
Total and cardiac death rates are increased in winter versus summer.
The factors influencing this seasonal variation are not well studied.

METHODS
We obtained daily death certificate data from health departments in a variety of climates (Texas [TX], Arizona [AZ], Georgia [GA], Los Angeles [LA], Washington [WA], Pennsylvania [PA], Massachusetts [MA]) from 1/1/05 through 12/31/08 and compared them. Average seasonal values for each day of the year were obtained by calculating a 19-day centered moving average (to smooth the curve) and taking the average values of the 4 years’ curves.

RESULTS
Average seasonal values varied by location but all locations revealed a “U” shaped curve with peaks in winter and troughs in summer (Figure 1).
Using raw daily death rates, the peak 8 day period was significantly greater than the trough 8 day period (p<0.0001 for each location).

Total death rates parallel circulatory death rates. The data were normalized to (divided by) the average annual death rate for that location (Figure 2) revealing very similar patterns in the difference between peak versus trough despite very different climates. The maximum % change (using the peak 8 day period and the trough 8 day period) was calculated using raw daily death rates. Maximum % change was similar, 26-36% across a wide spectrum of climates (p = NS between locations) (Figure 2).

CONCLUSIONS
While different locations report different average total and circulatory death rates, when normalized by average annual death rate the “U” curves are superimposed suggesting an acclimatization phenomenon. There is a 26-36% greater death rate in winter than summer despite different locations and climates.

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Figure 1: Circulatory Death Rate

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Figure 2: Normalized Circulatory Death Rate

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Figure 2a: Note that Arizona and Mass. have similar ranges

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Attached files

ID Name Comment Uploaded Size Downloads
1697 Season max change.jpg admin 09 Nov, 2012 12:29 11.17 Kb 702
1696 Season2.jpg admin 09 Nov, 2012 12:28 32.26 Kb 732
1695 Season1.jpg admin 09 Nov, 2012 12:28 27.72 Kb 755
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