(April 2009) When some people reach older ages, they begin to lose their ability to reason and to remember. For at least one in every 12 elderly people, the decline in cognitive function is so severe they have difficulty performing the normal activities of daily living, and eventually, cannot live independently.

With continued population aging—the number of Americans ages 65 or older is projected to swell from around 41 million to 65 million over the next 15 years—the loss of cognitive function among some older Americans foreshadows a potentially enormous social and economic burden on individuals, families, communities, and the nation. The U.S. National Institutes on Aging Division of Behavioral and Social Research is funding research to find out more about declines in cognitive functioning among older Americans. What are the recent trends? What factors are associated with a faster or slower decline? The answers to these questions are relevant for policymaking in a wide variety of areas.

Kenneth Langa, University of Michigan School of Medicine and Institute for Social Research, has conducted research using data from the national Health and Retirement Study. Results from Langa's study show that cognitive impairment among Americans ages 70 or older declined between 1993 and 2002, from 12.2 percent to 8.7 percent. Langa and his colleagues attribute this improvement to several factors, including more effective treatment of stroke and heart disease—risk factors for dementia—and increased educational levels of older Americans. Average educational attainment for participants in the 2002 study was almost one year greater than for those in the 1993 study.

But Langa warns that other trends may adversely affect the brain health of Americans, especially rising obesity rates and a consequent increase in diabetes, which is also associated with declining cognitive function among older adults.

In this interview, Langa discusses cognitive impairment and its causes, trends, and effects in the United States.