Dietary protein intake in midlife in relation to healthy aging - results from the prospective Nurses' Health Study cohort

Abstract

Background: Protein intake plays an important role in maintaining the health status of older adults. However, few epidemiologic studies examined midlife protein intake in relation to healthy aging.

Objectives: The objective of this study was to evaluate the long-term role of dietary protein intake in healthy aging among female participants in the prospective Nurses' Health Study (NHS) cohort.

Methods: We included 48,762 NHS participants aged <60 y in 1984. Total protein, animal protein, dairy protein (a subset of animal protein), and plant protein were derived from validated food frequency questionnaires. Healthy aging was defined as being free from 11 major chronic diseases, having good mental health, and not having impairments in either cognitive or physical function, as assessed in the 2014 or 2016 NHS participant questionnaires. We used multivariate logistic regression adjusted for lifestyle, demographics, and health status to estimate the odds ratios (ORs) and 95% confidence intervals for protein intake in relation to healthy aging.

Results: A total of 3721 (7.6%) NHS participants met our healthy aging definition. Protein intake was significantly associated with higher odds of healthy aging. The ORs (95% confidence intervals) per 3%-energy increment with healthy aging were 1.05 (1.01, 1.10) for total protein, 1.07 (1.02, 1.11) for animal protein, 1.14 (1.06, 1.23) for dairy protein, and 1.38 (1.24, 1.54) for plant protein. Plant protein was also associated with higher odds of absence of physical function limitations and good mental status. In substitution analyses, we observed significant positive associations for the isocaloric replacement of animal or dairy protein, carbohydrate, or fat with plant protein (ORs for healthy aging: 1.22-1.58 for 3% energy replacement with plant protein).

Conclusions: Dietary protein intake, especially plant protein, in midlife, is associated with higher odds of healthy aging and with several domains of positive health status in a large cohort of female nurses.

Keywords: animal protein; diet; healthy aging; lifestyle; plant protein; protein.

FIGURE 1

Odds ratios (ORs) (95% confidence intervals) of healthy aging (n = 3721) associated with isocaloric substitution of protein (total, animal, dairy, and plant) for dietary carbohydrate (total, refined, and from whole grains) and dietary fatty acids (total, saturated, polyunsaturated, and trans) modeled in 3%-energy increments in 48,762 participants in the Nurses’ Health Study.^1,2 BMI, body mass index; CI, confidence interval; MET, metabolic equivalent; MUFA, monounsaturated fatty acid; OR, odds ratio; PUFA, polyunsaturated fatty acid; SFA, saturated fatty acid; TFA, trans fatty acid. ¹The isocaloric substitutions can be interpreted as the effect of substituting 3% of calories contributed by a given dietary protein variable for the corresponding calories contributed by either dietary carbohydrate or dietary fat variables on the odds of healthy aging. For each comparison, we simultaneously included each protein variable and the corresponding replacement macronutrient in a multivariate logistic, both modeled continuously. The ORs and 95% CIs for the isocaloric substitution association were derived from the difference between the regression coefficients for each variable. ²To assess the substitution associations for total, whole grain, or refined-grain carbohydrates, we used multivariate logistic models adjusted for baseline age (continuous), race (White, other), education (registered nurse, bachelor, or graduate), marital status (married, other), postmenopausal hormone use (premenopausal; never, past user, the current user), smoking status (never smoked; former smoker, 0.1–14.9, 15.0–29.9, >30 pack-y), alcohol intake (0, 0.1–4.9, 5.0–14.9, >15.0 g/d), physical activity (<3, 3–8.9, 9–17.9, 18–26.9, >27 MET/wk); BMI (averaged 1984 and 1986; <22.5, 22.5–24.9, 25.0–27.5, 27.5–30.0, 30.0–34.9, >35.0), baseline history of hypertension or hypercholesterolemia (yes, no); aspirin use (never, past, current); multivitamin use (yes, no), and total energy intake (kcal/d, continuous) We used the same multivariate logistic model to assess the substitution associations for the fat variables. Of note, we simultaneously included SFA, PUFA, MUFA, and TFA variables in the same model. ³Refined carbohydrate was defined as the sum of carbohydrates from refined grains, potatoes, and added sugar