Associations of Protein Intake and Protein Source with Bone Mineral Density and Fracture Risk: A Population-Based Cohort Study

Abstract

High dietary protein has been hypothesized to cause lower bone mineral density (BMD) and greater fracture risk. Previous results are conflicting and few studies have assessed potential differences related to differing protein sources.

Objective: To determine associations between total protein intake, and protein intake by source (dairy, non-dairy animal, plant) with BMD, BMD change, and incident osteoporotic fracture.

Design/setting: Prospective cohort study (Canadian Multicentre Osteoporosis Study). Participants/Measures: Protein intake was assessed as percent of total energy intake (TEI) at Year 2 (1997-99) using a food frequency questionnaire (N=6510). Participants were contacted annually to ascertain incident fracture. Total hip and lumbar spine BMD was measured at baseline and Year 5. Analyses were stratified by group (men 25-49 y, men 50+ y, premenopausal women 25-49 y, and postmenopausal women 50+ y) and adjusted for major confounders. Fracture analyses were limited to those 50+ y.

Results: Intakes of dairy protein (with adjustment for BMI) were positively associated with total hip BMD among men and women aged 50+ y, and in men aged 25-49. Among adults aged 50+ y, those with protein intakes of <12% TEI (women) and <11% TEI (men) had increased fracture risk compared to those with intakes of 15% TEI. Fracture risk did not significantly change as intake increased above 15% TEI, and was not significantly associated with protein source.

Conclusions: In contrast to hypothesized risk of high protein, we found that for adults 50+ y, low protein intake (below 15% TEI) may lead to increased fracture risk. Source of protein was a determinant of BMD, but not fracture risk.

Figure 1

Flowchart detailing Canadian Multicentre Osteoporosis Study participants with exposure assessment at Year 2, exclusions from the regression analyses for BMD and fracture outcomes^,and study sample size for each outcome

Figure 2

The Cross-sectional Association between Protein Intake (Dairy, Non-dairy Animal, Plant) as % TEI and Year 5 BMD (TotalHip and Lumbar Spine) adjusted for BMI Data are shown as betas and error bars indicate the range of the 95% CI. Regression analysis done with standardized variables, dairy protein: 1 SD=2.3% TEI, non-dairy animal protein: 1 SD=1.9% TEI, plant protein: 1 SD=1.5% TEI. All models adjusted for age, height, TEI, center, education, smoking, alcohol intake, physical activity, sedentary hours, calcium and vitamin D supplement use, hormone therapy (women 50+ y), bisphosphonate use (50+ y), and diagnosis of osteoporosis (50+ y).

Figure 3

The Association between Protein Intake as % of Total Energy Intake (%TEI) and Incident Fragility (Low-Trauma) Fracture and Incident Main Fracture among Men 50+ y and Postmenopausal Women 50+ y The solid black line is the hazard ratio, while the dotted lines indicate the range of the 95% CI. All models adjusted for age, height, TEI, center, education, smoking, alcohol intake, physical activity, sedentary hours, calcium and vitamin D supplement use, hormone therapy (women only), bisphosphonate use (women only), and diagnosis of osteoporosis (women only).