Moderate consumption of freeze-dried blueberry powder increased net bone calcium retention compared with no treatment in healthy postmenopausal women: a randomized crossover trial

Abstract

Background: Preclinical studies suggest that blueberry consumption is associated with improved bone health.

Objectives: We conducted a blueberry dose-response study in ovariectomized (OVX)-rats that informed a study in postmenopausal women using the urinary appearance of calcium (Ca) tracers from prelabeled bone to reflect changes in bone balance. We hypothesized that blueberry consumption would reduce bone loss in a dose-dependent manner compared with no treatment.

Methods: OVX rats were fed 4 doses of blueberry powder (2.5%, 5%, 10%, and 15%) in randomized order to determine bone ⁴⁵Ca retention. Fourteen healthy, nonosteoporotic women ≥4 y past menopause were dosed with 50 nCi of ⁴¹Ca, a long-lived radioisotope, and equilibrated for 5 mo to allow ⁴¹Ca deposition in bone. Following a 6-wk baseline period, participants were assigned to a random sequence of 3 6-wk interventions, a low (17.5 g/d), medium (35 g/d), or high (70 g/d) dose of freeze-dried blueberry powder equivalent to 0.75, 1.5, or 3 cups of fresh blueberries incorporated into food and beverage products. Urinary ⁴¹Ca:Ca ratio was measured by accelerator mass spectrometry. Serum bone resorption biomarkers and urinary polyphenols were measured at the end of each control and intervention period. Data were analyzed using a linear mixed model and repeated measures analysis of variance.

Results: In both OVX rats and postmenopausal women, blueberry interventions benefited net bone calcium balance at lower but not at higher doses. In women, net bone calcium retention increased by 6% with the low (95% CI: 2.50, 8.60; P < 0.01) and 4% with the medium (95% CI: 0.96, 7.90; P < 0.05) dose compared with no treatment. Urinary excretion of hippuric acid increased dose-dependently with blueberry consumption. No significant relationships were found between bone resorption biomarkers, 25-hydroxyvitamin D, and interventions.

Conclusions: Moderate consumption (<1 cup/d) of blueberries may be an effective strategy to attenuate bone loss in healthy postmenopausal women. This trial was registered at clinicaltrials.gov as NCT02630797.

Keywords: blueberries; bone; calcium; osteoporosis; polyphenols; postmenopausal.

FIGURE 1

CONSORT chart. The chart shows participant progress through the study phases.

FIGURE 2

Human study design. Participants were dosed with ⁴¹Ca and completed a 5-mo equilibration, a 6-wk baseline, and a random sequence of 3 interventions, each followed by a 6-wk washout. Urine was collected over 24 h weekly during the intervention and every 3 wk during washout for the assessment of primary outcome, net bone calcium retention. Secondary outcomes, including bone metabolism biomarkers, serum calcium, vitamin D, and urinary polyphenolics, were measured in fasting blood collected at the end of each study period.

FIGURE 3

Hormetic effect of BB powder on bone balance in 20 OVX female rats. The net bone calcium retention increased with the lowest dose of BB power, showed a trend toward an increase with the moderate dose, and no effect with the highest dose compared with no treatment. Data are means and 95% CI, ∗P < 0.05, n = 20. BB, blueberry; OVX, ovariectomized.

FIGURE 4

Change in net bone calcium retention as measured by urinary ⁴¹Ca:Ca ratio in postmenopausal women consuming low (17.5 g/d), medium (35 g/d), and high dose (70 g/d) of freeze-dried BB powder compared with no treatment. Net bone calcium retention is expected to increase above the control line (dotted line) whenever a treatment reduces bone resorption. Our results showed that the net bone calcium retention increased with the low and medium doses of BB power compared with no treatment. Data were analyzed with the use of a linear mixed model. Data are means and 95% CI, ∗P < 0.05, ∗∗P < 0.01, n = 13. BB, blueberry.

FIGURE 5

Serum RANKL(A), RANKL/OPG ratio (B), and P1NP concentration in postmenopausal women at baseline (0 g/d) and after the intervention with low (17.5 g/d), medium (35 g/d), and high dose (70 g/d) of freeze-dried BB powder. Bone resorption marker RANKL was significantly reduced by the medium dose of BB powder. Bone formation marker P1NP was reduced by the low, medium, and high doses of BB powder. Data were analyzed by RM ANOVA followed by Dunnett’s post hoc test. Data are means ± SD, ∗P < 0.05, ∗∗P < 0.01, n = 13. BB, blueberry; OPG, osteoprotegerin; P1NP, procollagen type 1 N-terminal propeptide; RANKL, receptor activator of nuclear factor kappa-Β ligand.

FIGURE 6

Urinary polyphenolics and their metabolites: total polyphenols (A), hippuric acid (B), phenolic acids (C), and anthocyanins (D) normalized to creatinine in postmenopausal women without (0 g/d) and after the intervention with low (17.5 g/d), medium (35 g/d), and high dose (70 g/d) of freeze-dried BB powder. Urinary excretion of hippuric acid was higher during the high-dose intervention compared with baseline. Data were analyzed by RM ANOVA followed by Dunnett’s post hoc test. Data are means ± SD, ∗P < 0.05, ∗∗P < 0.01, n = 14. BB, blueberry.