Longer life spans are scarred by more number of years of sickness than before, reveals a new study.

Indeed, a 20-year-old today can expect to live one less healthy year over his or her life span than a 20-year-old a decade ago, even though life expectancy has grown.

From 1970 to 2005, the probability of a 65-year-old surviving till age 85 has doubled from about a 20 percent chance to a 40 percent chance, reports the Journal of Gerontology.

But new research from Prof Eileen Crimmins, gerontologist at the University of Southern California, and Hiram Beltran-Sanchez, Crimmins` junior colleague, shows that the period spent with a serious disease or loss of functional mobility has actually increased in the last few decades.

`There is substantial evidence that we have done little to-date to eliminate or delay disease while we have prevented death from diseases,` Crimmins explained, according to a Southern California release.

`At the same time, there have been substantial increases in the incidences of certain chronic diseases, specifically, diabetes.`

A 20-year-old male in 1998 could expect to live another 45 years without at least one of the leading causes of death: cardiovascular disease, cancer or diabetes.

The number fell to 43.8 years in 2006, the loss of more than a year. For young women, expected years of life without serious disease fell from 49.2 years to 48 years over the last decade.

At the same time, the number of people who report lack of mobility has grown, starting with young adults.

Functional mobility is defined as the ability to walk up 10 steps, walk a quarter mile, stand or sit for two hours, and stand, bend or kneel without using special equipment.