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Changing seasonality of mortality from coronary heart disease
D Seretakis1, P Lagiou, L Lipworth
1Department of Epidemiology, Harvard School of Public Health, Boston, MA 02115, USA.
Insights
Seasonal coronary heart disease deaths have changed, with reduced winter peaks. This shift correlates with increased home heating and air conditioning use over time.
Area of Science:
- Environmental Health
- Epidemiology
- Cardiovascular Disease Research
Background:
- Coronary heart disease (CHD) is a leading cause of mortality in the United States.
- CHD mortality exhibits a seasonal pattern, with higher rates during winter months.
- Identifying risk factors for CHD is crucial for public health initiatives.
Purpose of the Study:
- To analyze temporal changes in the seasonal pattern of coronary mortality.
- To investigate the hypothesis that reduced exposure to extreme temperatures influences this seasonal pattern.
- To explore the impact of environmental factors on cardiovascular disease mortality.
Main Methods:
- Utilized published U.S. coronary mortality data from 1937-1991.
- Employed sine curve fitting to analyze monthly death frequencies and seasonal patterns.
- Examined trends in the peak-to-trough ratio of seasonal mortality curves over time.
Main Results:
- A significant decline in the seasonal peak-to-trough ratio was observed until approximately 1970, indicating a flattening of the seasonal pattern.
- The trend reversed post-1970, suggesting a potential re-emergence or stabilization of seasonal variations.
- Regional analysis showed a steeper decline in seasonal variation in New England compared to the South.
Conclusions:
- The seasonal patterns of coronary mortality in the U.S. have demonstrably changed over the study period.
- These changes are consistent with increased adoption of residential heating and air conditioning.
- Environmental microclimate modifications may partially explain socioeconomic disparities in cardiovascular mortality.
Context:
Coronary heart disease is the major cause of mortality in the United States. Factors associated with coronary risk are important to identify. Coronary mortality is greater during the winter months.
Objective:
To investigate whether declining coronary mortality has been accompanied by a change in the seasonal pattern and to investigate the hypothesis that diminishing exposures to environmental cold and heat have affected the seasonal pattern.
Design:
We used published data on coronary mortality by year to evaluate the time trend in the seasonal pattern. We fit a sine curve to the monthly frequency of deaths in each year and examined the trend over time in the ratio of the peak to the trough of the curve.
Setting:
We used monthly coronary deaths in the United States from 1937 through 1991. Deaths by cause and month were not available by geographic area within the United States, but we were able to examine total monthly deaths in 2 regions with contrasting climates, New England and the South.
Outcome Measures:
We used the yearly peak-to-trough ratio as our primary outcome and assessed its trend over time by linear regression. We also depicted the time trends using polynomial smoothing.
Results:
The peak-to-trough ratio diminished by about 2% per year until around 1970, when the trend reversed. In New England, the decline was steeper than in the South, as measured from all deaths.
Conclusion:
Seasonal patterns in coronary mortality in the United States have changed with time. These changes are compatible with the gradual expansion of adequate heating and the subsequent increased use of air-conditioning. Microclimatic influences on coronary mortality could explain in part the socioeconomic gradient of cardiovascular mortality.