Americans are living longer but in poorer health, according to a new study.

The USC-led study examined life expectancy trends and disability rates in a 40-year period, from 1970 to 2010. The analysis of U.S. vital statistics found that the average total lifespan increased for men and women in those 40 years, but so did the proportion of time spent living with a disability.

The study found increased longevity is not necessarily indicative of good health. Most age groups live longer with a disability or other health problem.

"We could be increasing the length of poor quality life more than good-quality life," lead author Eileen Crimmins, USC University Professor and AARP Professor of Gerontology at the USC Davis School of Gerontology. "There are a number of indications that the Baby Boomer generation that is now reaching old age is not seeing improvements in health similar to the older groups that went before them." Only for people aged 65 and older was there a "compression of morbidity" -- a reduction in the proportion of years spent with disability.

The findings have significant implications for policymaking, such as proposals to raise the retirement age for Social Security and Medicare eligibility.

"Clearly, there is a need to maintain health and reduce disability at younger ages to have meaningful compression of morbidity across the age range," Crimmins said. "The trends for the last 40 years do not support projections and policies that are based on assumptions of a reduced length of disabled life."

Findings

The average lifespan for men increased by 9.2 years to 76.2 years, the researchers found. The number of years they live with a disability increased by 4.7 years while the number of years spent disability-free increased by 4.5 years.

For women, the average lifespan increased by 6.4 years to 81 years. The number of years that women spend with a disability increased by 3.6 years, exceeding the increase in women's disability-free life (2.7 years).

"The smaller increase in healthy life than in total life for women was surprising and another indication that American women have not done as well as American men in terms of improving health in recent decades," Crimmins said.

Different factors may affect disability at different ages. For instance, younger populations may have had an increase in disability because of a greater emphasis on mental health, increased diagnoses of autism spectrum and attention-deficit hyperactivity disorders, and changes in drug use.

The study, "Trends Over 4 Decades in Disability-Free Life Expectancy in the United States," was published online Wednesday in the American Journal of Public Health. Yuan Zhang of the USC Leonard Davis School of Gerontology and Yasuhiko Saito, a USC graduate and faculty member at Nihon University, were co-authors.

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The study was supported by a grant from the US National Institute on Aging (P30-AG17265) and a Special Research Grant by the Japan Ministry of Health, Labour and Welfare (H26-Tokubetsu-Shitei-029).