Assessing the respective contributions of dietary flavanol monomers and procyanidins in mediating cardiovascular effects in humans: randomized, controlled, double-masked intervention trial

Abstract

Background: Flavanols are an important class of food bioactives that can improve vascular function even in healthy subjects. Cocoa flavanols (CFs) are composed principally of the monomer (-)-epicatechin (∼20%), with a degree of polymerisation (DP) of 1 (DP1), and oligomeric procyanidins (∼80%, DP2-10).

Objective: Our objective was to investigate the relative contribution of procyanidins and (-)-epicatechin to CF intake-related improvements in vascular function in healthy volunteers.

Design: In a randomized, controlled, double-masked, parallel-group dietary intervention trial, 45 healthy men (aged 18-35 y) consumed the following once daily for 1 mo: 1) a DP1-10 cocoa extract containing 130 mg (-)-epicatechin and 560 mg procyanidins, 2) a DP2-10 cocoa extract containing 20 mg (-)-epicatechin and 540 mg procyanidins, or 3) a control capsule, which was flavanol-free but had identical micro- and macronutrient composition.

Results: Consumption of DP1-10, but not of either DP2-10 or the control capsule, significantly increased flow-mediated vasodilation (primary endpoint) and the concentration of structurally related (-)-epicatechin metabolites (SREMs) in the circulatory system while decreasing pulse wave velocity and blood pressure. Total cholesterol significantly decreased after daily intake of both DP1-10 and DP2-10 as compared with the control.

Conclusions: CF-related improvements in vascular function are predominantly related to the intake of flavanol monomers and circulating SREMs in healthy humans but not to the more abundant procyanidins and gut microbiome-derived CF catabolites. Reduction in total cholesterol was linked to consumption of procyanidins but not necessarily to that of (-)-epicatechin. This trial was registered at clinicaltrials.gov as NCT02728466.

Figures

FIGURE 1

Schematic of the fate of cocoa flavanols in the gastrointestinal tract. Only the monomeric flavanol (−)-epicatechin is absorbed in the small intestine and metabolized to the major SREMs (–)-epicatechin-3′-O-glucuronide, 3′-O-methyl-(–)-epicatechin-5-sulfate, and (–)-epicatechin-3′-sufate. Oligomeric procyanidins are neither absorbed nor metabolized in the small intestine. Both monomers and procyanidins are catabolized by gut microbes in the colon, leading to ring fission products including γVL, which, in turn, is absorbed and further metabolized to γVLMs. DP, degree of polymerization; SREM, structurally related (−)-epicatechin metabolite; γVL, 5-(3′,4′-dihydroxyphenyl)-γ-valerolactone; γVLM, phase II γVL metabolite.

FIGURE 2

CONSORT study flow. CONSORT, Consolidated Standards of Reporting Trials; DP, degree of polymerization.

FIGURE 3

Changes in values of FMD from baseline at 2 h, 1 mo, and 2 h at 1 mo after supplementation of the following: 1) DP1–10, standardized cocoa extract that contains monomeric flavanols, mainly (−)-epicatechin, and procyanidins with a DP that ranges from 2 to 10; 2) a cocoa extract that contains predominantly procyanidins (DP2–10); or 3) a flavanol-free control (Control) (see Table 1 for their compositions). Time × intervention interaction, P = 0.101; main effect of intervention, P < 0.001; repeated-measurements ANCOVA with baseline values as covariates with Bonferroni post hoc test. Values are means ± SEMs. *P < 0.05 vs. DP2–10. #P < 0.05 vs. Control. DP, degree of polymerization; FMD, flow-mediated vasodilation.

FIGURE 4

(A) Changes in plasma SREMs from baseline at 2 h, 1 mo, and 2 h at 1 mo after supplementation of the following: 1) DP1–10, a standardized cocoa extract that contains monomeric flavanols, mainly (−)-epicatechin, and procyanidins with a DP that ranges from 2 to 10; 2) a cocoa extract that contains predominantly procyanidins (DP2–10); or 3) a flavanol-free control (Control) (see Table 1 for their compositions). Time × intervention interaction, P < 0.001; main effect of intervention, P < 0.001; repeated-measurements ANCOVA with baseline values as covariates with Bonferroni post hoc test. Amount of SREMs (B) and γVL metabolites (C) excreted over 24 h in urine on day 1 and the last day of study at 1 mo (time by intervention interactions P = 0.325 and P = 0.467 and main effects of intervention, each P < 0.001; repeated-measurements ANOVA with Bonferroni post hoc test). All values are means ± SEMs. *P < 0.05 vs. DP2–10; #P < 0.05 vs. Control. DP, degree of polymerization; SREM, structurally related (−)-epicatechin metabolite; γVL, 5-(3′,4′-dihydroxyphenyl)-γ-valerolactone.

FIGURE 5

Changes in SBP (A) and PWV (B) from baseline at 2 h, 1 mo, and 2 h at 1 mo and total cholesterol (C) at 1 mo after supplementation of the following: 1) DP1–10, a standardized cocoa extract that contains monomeric flavanols, mainly (−)-epicatechin, and procyanidins with a DP that ranges from 2 to 10; 2) a cocoa extract that contains predominantly procyanidins (DP2–10); or 3) a flavanol-free control (Control) (see Table 1 for their compositions). Repeated-measurements ANCOVA (A, B) and univariate ANCOVA (C), with baseline values as covariates with Bonferroni post hoc test; time × intervention interactions, P = 0.291 (A) and P = 0.176 (B); main effects of intervention, P = 0.047 (A), P < 0.001 (B), and P = 0.007 (C) .Values are means ± SEMs. *P < 0.05 vs. DP2–10; #P < 0.05 vs. Control. DP, degree of polymerization; PWV, pulse wave velocity; SBP, systolic blood pressure.