Does Low Body Mass Index Matter? Relationship between Body Mass Index and Subjective Well-Being among Long-Lived Women over 95 Years of Age.

OBJECTIVES

To examine the relationship between body mass index (BMI) and subjective well-being (SWB) among long-lived women over 95 years of age and evaluate whether this relationship is mediated by functional ability.

DESIGN

Retrospective cohort study.

SETTING

Data from the Rugao longevity cohort, a population-based study in Rugao, China.

PARTICIPANTS

A sample of 342 long-lived women (mean age 97.4 ± 2.1, range 95-107) whose SWB and other covariates were available were included in this study.

MEASUREMENTS

BMI was calculated as weight in kilograms divided by height in meters-squared (kg/m(2)). SWB was measured by life satisfaction (LS), positive affect (PA), negative affect (NA) and affect balance (AB). Functional ability was assessed by the Katz Index of Activities of Daily Living (ADL).

RESULTS

According to BMI classification standards for China, the underweight group had lower levels of LS than the normal and overweight groups (28.62 vs. 30.51 and 31.57, respectively; p<.05). Correlation analysis showed that BMI was significantly related to LS (r = 0.166, p<.01). The strength of the BMI and LS association was diminished when ADL was included in the general linear regression models. Mediation analysis revealed that ADL mediated this relationship (effect size = 22.6%). We did not observe significant associations of BMI with other SWB components (PA, NA, and AB).

CONCLUSION

For long-lived women, low BMI, rather than elevated BMI, is an indicator of poor psychological well-being. The findings call for public health awareness about low body weight in long-lived women, especially in those with physical disabilities when focusing on quality of life.