Is the relationship between BMI and mortality increasingly U-shaped with advancing age? A 10-year follow-up of persons aged 70-95 years

Abstract

Background: In the call for papers (Alley DE, Ferrucci L, Barbagallo M, Studenski SA, Harris TB. A research agenda: the changing relationship between body weight and health in aging. J Gerontol A Biol Sci Med Sci. 2008;63(11):1257-1259.), it is assumed that the association between body mass index (BMI [kilogram per square meter]) and mortality becomes increasingly U-shaped with advancing age. The aim of this study is to examine the association between BMI and mortality and to test whether the association is changing with advancing age for persons aged 70-95 years in Denmark.

Methods: The study populations comprised two surveys: the Longitudinal Study of Aging of Danish Twins (LSADT) and the Danish 1905 Cohort Survey. From 1995 to 1999, 4253 individuals aged 70-95 years from the LSADT were interviewed at home. In 1998, 2,262 individuals aged 92-93 years from the 1905 Cohort were interviewed at home. The information in both surveys included self-reported weight and height. With virtually no loss to follow-up, survival was assessed through a 10-year follow-up period, during which 4,664 (72%) of the persons died.

Results: The association between BMI and mortality is changing with advancing age for people aged 70-95 years. There was a significant decrease in the association between mortality and low BMI with advancing age for both genders (p < or = .03). There was also a tendency for the association between mortality and high BMI to decrease with advancing age for males (p = .06).

Conclusion: In a large contemporary Danish population-based sample, the association of BMI and mortality became decreasingly U-shaped with advancing age for the age range 70-95 years.

Figure 1.

Graphical representation of the linear spline Cox regression for each gender and age groups.

Figure 2.

Linear trend analysis for the hazard ratio with an increment of 1.0 in body mass index (BMI) according to age groups having a low (below knot) or high (above knot) BMI for each gender. The hazard ratios are from the separate linear spline models of the four age groups. The bars represent 95% confidence intervals. The p value refers to a linear trend test. The graph on the left shows that the association between mortality and low BMI decreases with advancing age, and the graph on the right also shows that the association between mortality and high BMI decreases with advancing age.