Prior to reaching the golden years, too much body fat tends to increase the risk of dying, but extra weight may have the opposite effect for older adults, a new study hints.

Higher fat mass in older adults “is thought to be an energy reserve that helps the individual survive illnesses and chronic conditions,” Dr. Jennifer L. Kuk, from York University in Toronto, Canada, noted in an email to Reuters Health.

The study she co-conducted with Dr. Chris I. Ardern, also from York University, seems to bear this out. In the study, many lower weight and body fat indicators were associated with a greater risk of dying among men and women aged 65 and older.

Among individuals older than 75, having a low versus a normal body weight seemed to raise the risk of death from any cause by a factor of 1.6 in men and nearly 3 in women, they report in the Journal of the American Geriatrics Society.

Kuk and Ardern used data from the Third National Health and Nutrition Examination Survey conducted between 1988 and 1994 to assess body mass, waist circumference, waist-to-hip ratio, hip circumference, and other body mass and body fat indicators among 4,437 men and 5,166 women. Overall, 1,116 of them were 65 to 75 years old and 1,200 were older than 75 years.

Over an average of 8.7 years, 1,466 study participants died.

As expected, the fewest deaths - 4 percent in men and 3.5 percent in women - occurred among those 18 to 64 years old. In this group, the risk of death was increased in obese men and in overweight and obese women.

But in the older groups, being underweight was associated with greater mortality, whereas being overweight was associated with lower mortality.

When considering risk of death, obesity may be a greater concern in younger than older adults, the researchers say. Weight management should continue to be a target for reductions in illness and death in younger individuals, they add.

However, in light of their findings, although weight loss may improve risk for various co-existing illnesses associated with obesity, “the appropriateness of weight loss as an intervention to extend longevity in older populations is unclear and warrants further investigation,” Kuk and Ardern conclude.

SOURCE: Journal of the American Geriatrics Society, November 2009.