Protein Intake and Incident Frailty in the Women's Health Initiative Observational Study

Jeannette M. Beasley, PhD, MPH, RD; Andrea Z. LaCroix, PhD; Marian L. Neuhouser, PhD; Ying Huang, PhD; Lesley Tinker, PhD; Nancy Woods, PhD; Yvonne Michael, PhD; J. David Curb, MD; Ross L. Prentice, PhD

Disclosures

J Am Geriatr Soc. 2010;58(6):1063-1071. 

In This Article

Abstract and Introduction

Abstract

Objectives: To evaluate the association between protein intake and incident frailty.
Design: Prospective cohort study.
Setting: Subset of the Women's Health Initiative Observational Study conducted at 40 clinical centers.
Participants: Twenty-four thousand four hundred seventeen women aged 65 to 79 who were free of frailty at baseline with plausible self-reported energy intakes (600–5,000 kcal/day) according to the Food Frequency Questionnaire (FFQ).
Measurements: Baseline protein intake was estimated from the FFQ. Calibrated estimates of energy and protein intake were corrected for measurement error using regression calibration equations estimated from objective measures of total energy expenditure (doubly labeled water) and dietary protein (24-hour urinary nitrogen). After 3 years of follow-up, frailty was defined as having at least three of the following components: low physical function (measured using the Rand-36 questionnaire), exhaustion, low physical activity, and unintended weight loss. Multinomial logistic regression models estimated associations for uncalibrated and calibrated protein intake.
Results: Of the 24,417 eligible women, 3,298 (13.5%) developed frailty over 3 years. After adjustment for confounders, a 20% increase in uncalibrated protein intake (%kcal) was associated with a 12% (95% confidence interval (CI)=8–16%) lower risk of frailty, and a 20% increase in calibrated protein intake was associated with a 32% (95% CI=23–50%) lower risk of frailty.
Conclusion: Higher protein consumption, as a fraction of energy, is associated with a strong, independent, dose-responsive lower risk of incident frailty in older women. Using uncalibrated measures underestimated the strength of the association. Incorporating more protein into the diet may be an intervention target for frailty prevention.

Introduction

Frailty is a geriatric syndrome characterized by slowness, weakness, fatigue, low physical activity, and unintentional weight loss.[1] Frail older individuals are at substantially greater risk of many adverse health outcomes, including falls, fractures, development of disabilities, hospitalizations, and death.[2,3] Frailty is an increasingly important public health problem with the aging of the U.S. population; prevalence estimates of frailty from several population-based cohorts of women aged 65 and older range from 7.3% to 16.3%.[1,3,4]

The Health, Aging and Body Composition Study (Health ABC) recently reported that, over a 3-year period, participants in the highest quintile of protein intake lost approximately 40% less total lean mass than those in the lowest quintile.[5] This supports the hypothesis that increasing protein intake may confer protection against frailty. This hypothesis has not been examined in prospective, observational studies, many of which lack detailed dietary data or are limited by related measurement shortcomings.[6,7] The major question of clinical importance is whether the Institute of Medicine's Recommended Dietary Allowance (RDA) for protein of 0.8 g/kg per day[8] is adequate for elderly individuals, because recommendations were established based primarily on short-term nitrogen balance studies in young men,[9,10] and after 14 weeks of consuming 0.8 g/kg per day of protein, older adults lost muscle.[11]

The current study investigated protein intake in relation to incident frailty in the Women's Health Initiative Observational Study (WHI-OS). To improve upon self-reported protein intake, an approach for statistically correcting for measurement error using biomarkers for total energy and protein was employed.[12] Thus, this report compares association findings from crude self-reported intake with findings obtained using biomarker-calibrated intake estimates. Because higher-quality dietary protein is postulated to strengthen the protein frailty association,[13] the association between protein intake and frailty stratified according to the amount of essential amino acid or protein from animal (vs vegetable) sources was also examined.

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