Genetic and Environmental Factors in Average Longevity
Let’s return to Susie, who wonders whether she can expect to live a long life. What influences how long we will live on average? Our average longevity is influenced most by genetic, environmental, ethnic, and gender factors. Clearly, these factors interact; being from an ethnic minority group or being poor, for example, often means that one has a higher risk of exposure to a harmful environment and less access to high-quality health care. But it is important to examine each of these factors and see
how they influence our longevity. Let’s begin with genetic and environmental factors.
Genetic Factors. Living a long life has a clear, but probably complex, genetic link (Kirkwood, 2008). We have known for a long time that a good way to increase one’s chances of a long life is to come from a family with a history of long-lived individuals. For example, if your mother lives to at least age 80, roughly 4 years are added to your average longevity (Woodruff-Pak, 1988). Alexander Graham Bell (the same guy who received the credit for inventing the telephone) was one of the first people to demonstrate systematically the benefits of coming from a long-lived family. Bell considered 8,797 of William Hyde’s descendants and found that children of parents who had lived beyond 80 survived about 20 years longer than children whose parents had both died before they were 60. Thus Susie’s long-lived family sets the stage for Susie to enjoy a long life herself.
One exciting line of contemporary research, the Human Genome Project, completed in 2003, has mapped all our genes. This research and its spinoffs in microbiology and behavior genetics are continuing to produce some astounding results in terms of genetic linkages to disease and aging (you can track these through the main website of the Project, http:// www. ornl. gov/sci/techresources/Human_Genome/ research/spinoffs. shtml). Based on this gene mapping work, attempts are being made to treat diseases by improving the way that medications work and even by implanting “corrected” genes into people in the hopes that the good genes will reproduce and eventually wipe out the defective genes (Kanehisa et al., 2008). Payoffs from such research are helping us understand how increasing numbers of people are living to 100 or older. For example, research on people over age 100 (centenarians) in Italy showed a connection between genetics and ability to cope with disease (Franceschi et al., 2008). The oldest – old, such as Suzie’s grandmother, are hardy because they have a high threshold for disease and show slower rates of disease progression than their peers who develop chronic diseases at younger ages and die earlier.
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Environmental Factors. Although genes are a major determinant of longevity, environmental factors also affect the life span, often in combination with genes (Perls & Terry, 2003). Some environmental factors are more obvious; diseases, toxins, lifestyle, and social class are among the most important. Diseases, such as cardiovascular disease and Alzheimer’s disease, and lifestyle issues, such as smoking and exercise, receive a great deal of attention from researchers. Environmental toxins, encountered mainly as air and water pollution, are a continuing problem. For example, toxins in fish, bacteria and cancer-causing chemicals in drinking water, and airborne pollutants are major agents in shortening longevity.
The impact of social class on longevity results from the reduced access to goods and services, especially medical care, that characterizes most ethnic minority groups, the poor, and many older adults (National Center for Health Statistics, 2008a). Most of these people have little or no health insurance, and many cannot afford the cost of a more healthful lifestyle. For example, air pollution, poor
drinking water, and lead poisoning from old water pipes are serious problems in large urban areas, but many people simply cannot afford to move. How environmental factors influence average life expectancy changes over time. For example, acquired immunodeficiency syndrome (AIDS) has had a devastating effect on life expectancy in Africa, where in some countries (e. g., Botswana, Namibia, South Africa, Zimbabwe) average longevity may be reduced by as much as 30 years from otherwise expected levels (Kinsella & Phillips, 2005). In contrast, negative effects of cardiovascular diseases on average longevity are lessening as the rates of those diseases decline in many developed countries (National Center for Health Statistics, 2008a).
The sad part about most environmental factors is that we are responsible for most of them. Denying adequate health care to everyone, continuing to pollute our environment, and failing to address the underlying causes of poverty have undeniable consequences: They needlessly shorten lives and dramatically increase the cost of health care.