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18-03-2013 | Cardiology | Article

BMI linked to disease-specific mortality in very elderly Japanese

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medwireNews: Very elderly Japanese individuals should not let their body mass index (BMI) fall to below 22, warn researchers.

Ideally, people of this age should maintain their BMI between 22.5 and 23.8, say Yutaka Takata (Kyushu Dental University, Kitakyushu City, Japan) and colleagues, who investigated the association between BMI and disease-specific mortality in a population of individuals aged 80 years.

"Although many investigations have examined the relationship between body mass index (BMI) and mortality, little is known about the relationship between BMI and disease-specific mortality in very elderly people," they explain in the Archives of Gerontology and Geriatrics.

For the current study, the team measured BMI in 675 individuals living in Japan's Fukuoka Prefecture who were aged 80 years in 1998 and followed them up 12 years later.

Takata and team found that 397 (59%) of the individuals had died, 241 (36%) were alive, and 37 (5%) were unlocatable.

For the cases of death, the researchers created six groups according to BMI values: most thin (BMI <19.5 kg/m2), relatively thin (19.5 to <21.1 kg/m2), thin/normal (21.1 to <22.5 kg/m2), normal/overweight (22.5 to <23.8 kg/m2), relatively obese (23.8 to <26.0 kg/m2), and most obese (≥26.0 kg/m2).

Survival curve analysis showed that the most thin group had the lowest overall survival rate, significantly lower than in the normal/overweight, relatively obese, and most obese groups. By contrast, the normal/overweight group had the highest survival rate, significantly higher than in the most thin, the relatively thin, and the thin/normal groups.

Cox regression analysis showed that overall mortality and death due to cardiovascular disease (CVD) were highest in the most thin group and lowest in the normal/overweight group, with the most thin versus normal/overweight individuals at a 2.1-fold and 2.2-fold greater risk for overall mortality and CVD mortality, respectively.

"We surmise that the relationship between overall mortality and BMI could be influenced by that between cardiovascular mortality and BMI," writes the team.

Furthermore, mortality due to respiratory disease was highest in the most thin group and lowest in the most obese group, with the most thin group at a 5.1-fold greater risk for death from respiratory disease versus the most obese group.

"It may be that very old individuals (ie, near 80 years old) should keep their BMI around 23, and should avoid losing weight to a BMI less than 19.5," suggests the team.

By Sally Robertson, medwireNews Reporter

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