Magnesium intake, bone mineral density, and fractures: results from the Women's Health Initiative Observational Study

Abstract

Background: Magnesium is a necessary component of bone, but its relation to osteoporotic fractures is unclear.

Objective: We examined magnesium intake as a risk factor for osteoporotic fractures and altered bone mineral density (BMD).

Design: This prospective cohort study included 73,684 postmenopausal women enrolled in the Women's Health Initiative Observational Study. Total daily magnesium intake was estimated from baseline food-frequency questionnaires plus supplements. Hip fractures were confirmed by a medical record review; other fractures were identified by self-report. A baseline BMD analysis was performed in 4778 participants.

Results: Baseline hip BMD was 3% higher (P < 0.001), and whole-body BMD was 2% higher (P < 0.001), in women who consumed >422.5 compared with <206.5 mg Mg/d. However, the incidence and RR of hip and total fractures did not differ across quintiles of magnesium. In contrast, risk of lower-arm or wrist fractures increased with higher magnesium intake [multivariate-adjusted HRs of 1.15 (95% CI: 1.01, 1.32) and 1.23 (95% CI: 1.07, 1.42) for quintiles 4 and 5, respectively, compared with quintile 1; P-trend = 0.002]. In addition, women with the highest magnesium intakes were more physically active and at increased risk of falls [HR for quintile 4: 1.11 (95% CI: 1.06, 1.16); HR for quintile 5: 1.15 (95% CI: 1.10, 1.20); P-trend < 0.001].

Conclusions: Lower magnesium intake is associated with lower BMD of the hip and whole body, but this result does not translate into increased risk of fractures. A magnesium consumption slightly greater than the Recommended Dietary Allowance is associated with increased lower-arm and wrist fractures that are possibly related to more physical activity and falls.

Trial registration: ClinicalTrials.gov NCT00000611.

Figures

FIGURE 1.

Least-squares means (±SDs) of BMD at specified sites on the basis of quintiles of magnesium intake. Values were adjusted for covariates (age, race-ethnicity, parental history of fracture, personal fracture at ≥55 y of age, BMI, history of coronary heart disease, treated diabetes, self-reported health, hormone therapy use, alcohol intake, total calcium intake, smoking, and physical activity). *Quintile 5 compared with quintile 1, P < 0.001 (tests for linear trend across quintiles). BMD, bone mineral density.