Dietary Intervention Favorably Influences Physical Functioning: The Women's Health Initiative Randomized Dietary Modification Trial

Abstract

Background: In the Women's Health Initiative Dietary Modification randomized trial, the dietary intervention reduced breast cancer mortality by 21% (P = .02) and increased physical activity as well.

Objective: Therefore, the aim was to examine whether or not these lifestyle changes attenuated age-related physical functioning decline.

Design: In a randomized trial, the influence of 8 years of a low-fat dietary pattern intervention was examined through 20 years of cumulative follow-up.

Participants and setting: From 1993 to 1998, 48,835 postmenopausal women, ages 50 to 79 years with no prior breast cancer and negative baseline mammogram were randomized at 40 US clinical centers to dietary intervention or usual diet comparison groups (40 out of 60). The intervention significantly reduced fat intake and increased vegetable, fruit, and grain intake.

Main outcome measures: In post hoc analyses, physical functioning, assessed using the RAND 36-Item Short Form Health Survey, evaluated quality or limitations of 10 hierarchical physical activities. Longitudinal physical functioning, reported against a disability threshold (when assistance in daily activities is required) was the primary study outcome.

Statistical analyses performed: Semiparametric linear mixed effect models were used to contrast physical functioning trajectories by randomization groups.

Results: Physical functioning score, assessed 495,317 times with 11.0 (median) assessments per participant, was significantly higher in the intervention vs comparison groups through 12 years of cumulative follow-up (P = .001), representing a reduction in age-related functional decline. The intervention effect subsequently attenuated and did not delay time to the disability threshold. Among women in the dietary intervention vs comparison groups, aged 50 to 59 years, who were physically inactive at entry, a persistent, statistically significant, favorable influence on physical functioning with associated delay in crossing the disability threshold by approximately a year was seen (P value for interaction = .007).

Conclusions: In the Women's Health Initiative Dietary Modification randomized trial, a dietary intervention that significantly reduced breast cancer mortality also significantly reduced age-related functional decline through 12 years, which was attenuated with longer follow-up.

Keywords: Disability threshold; Low-fat dietary pattern; Physical functioning; Randomized trial; Women’s Health Initiative.