Four risk factors-all of them preventable-reduce life expectancy among U.S. men by 4.9 years and among U.S. women by 4.1 years, according to a study by the Harvard School of Public Health and the Institute for Health Metrics and Evaluation at the University of Washington. (According to U.N. figures, current U.S. life expectancy is 75.6 years for men and 80.8 years for women.)
The four factors are smoking, high blood pressure, elevated blood sugar, and being overweight or obese. Individually and together, the four factors lead to hundreds of thousands of deaths per year from such chronic diseases as diabetes, cardiovascular disease, and cancer.
For their study, the Harvard and Washington researchers used 2005 data from the National Center for Health Statistics, the National Health and Nutrition Examination Survey, and the Behavioral Risk Factor Surveillance System. They also conducted an extensive review of other studies on the effects of the four factors on mortality.
From those data, they extrapolated how many deaths could have been prevented if people had followed guidelines for reducing their exposure to the four factors. They then estimated the increase in life expectancy that avoidance of the risks would have added to people's lives.
The researchers also estimated the effects of the four risk factors on the longevity of eight distinct subgroups of Americans, which they called the "Eight Americas." The groups were identified by ethnicity, the counties in which they lived, and the affluence and educational levels of those counties. The Eight Americas included East Asians, three categories of low-income whites ("Middle America," "Northland," and Appalachia and Mississippi Valley residents), western Native Americans, and three categories of blacks (black "Middle America," high-risk urban blacks, and Southern low-income rural blacks). The reason for identifying ethnic, geographical, and socioeconomic characteristics, said the researchers, is to assist in developing public health strategies that intelligently and efficiently address the levels of risks in various groups.
Results showed that ethnicity and location were effective predictors of a person's life expectancy and general health: Among the findings:
- Western Native American men and Southern low-income rural black women have the highest body mass index
- Western Native American men and low-income whites in Appalachia and the Mississippi Valley are the biggest smokers
- Blacks, especially those in the rural South, have the highest blood pressure
- Whites have the lowest blood pressure
- Asian American men and women have the lowest body mass index, blood sugar levels, and levels of smoking
If only one of the four risk factors is eliminated, the estimated increase in life expectancy is:
- Smoking: 2.5 years for men, 1.8 years for women
- Blood pressure: 1.5 years for men, 1.6 years for women
- Obesity: 1.3 years for men, 1.3 years for women
- Blood sugar: 0.5 years for men, 0.3 years for women
The study appears in the March 23, 2010 issue of the journal PLos Medicine.
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