The Census Bureau reports, in 2003, there were 35.9 million people living in the U.S. who were 65 and older. Of those, 12.9 million were 75 to 84 and 4.7 million were 85 and older.

Currently, older people make up about 12 percent of the U.S. population. But as baby boomers age, their numbers will increase greatly. By 2030, the number of Americans 65 and older is expected to reach 72 million and account for 20 percent of the population.

There are important differences in the health, economic and social characteristics of today's older population compared to their counterparts a few generations ago. Back in 1900, the average life expectancy was 47.3 years. Only 17 percent of those 65 and older had ever graduated from high school and three percent from college. Today, a person born in 2000 has a life expectancy of 76.9 years. 72 percent of older people had graduated from high school and 17 percent had a bachelor's degree. In addition, older men and women are saving for retirement and are better prepared to live well in their retirement years.

Studying Life Characteristics

While Americans are living longer, disability and disease still continue to plague many older people. About 80 percent of those 65 and older have at least one chronic health condition (like arthritis, high blood pressure, heart disease or diabetes) and 50 percent have two or more conditions. Heart disease continues to be the leading cause of death in the U.S., followed by cancer and stroke.

Genetics play an important role in health and longevity, but other factors may also be involved. The best way to look at various factors that influence wellness is to follow patients through their lifespan in longitudinal studies.

The Wisconsin Longitudinal Study is the first large, ongoing survey of a selected population group in the U.S. It started in April 1957, when researchers pooled a random sample of more than 10,000 men and women graduating from Wisconsin high schools. The survey aimed to find out about students' social backgrounds, high school courses and activities and plans for the future. A follow-up survey was mailed to one-sixth of the parents six months later.

In the early 1960s, a researcher came across the original data and decided to perform a follow-up analysis. In 1964, a questionnaire was mailed to one-third of the original participants to determine their current social, economic and health status. The response was so good, investigators decided to continue periodic data collection from participants and their siblings. The periodic data collection enabled scientists to follow and study the life course of a large group of Americans beginning in late adolescence through adulthood and into their early/mid 60s.

Researchers have collected data on participants' educational achievement, occupational histories, income, assets, physical and mental health, and relationships with siblings, parents and offspring. The information may eventually be helpful in determining risk factors for disease, disability and early death. And now, DNA analysis will add to the information. Participants have submitted saliva samples that will help investigators look more closely at the roles of genes and environment in the risk for diseases, like Alzheimer's and depression.

For information on the Wisconsin Longitudinal Study:

http://www.disc.wisc.edu/wls/index.html

For general information on other longitudinal studies by the National Institute on Aging, http://www.nia.nih.gov/ResearchInformation/ScientificResources/LongitudinalStudiesallCurrent.htm.