Vascular endothelial function and oxidative stress are related to dietary niacin intake among healthy middle-aged and older adults

Abstract

We tested the hypothesis that vascular endothelial function and oxidative stress are related to dietary niacin intake among healthy middle-aged and older adults. In 127 men and women aged 48-77 yr, brachial artery flow-mediated dilation (FMD) was positively related to dietary niacin intake [%change (Δ): r = 0.20, P < 0.05; mmΔ: r = 0.25, P < 0.01]. In subjects with above-average dietary niacin intake (≥ 22 mg/day, NHANES III), FMD was 25% greater than in subjects with below-average intake (P < 0.05). Stepwise linear regression revealed that dietary niacin intake (above vs. below average) was an independent predictor of FMD (%Δ: β = 1.8; mmΔ: β = 0.05, both P < 0.05). Plasma oxidized low-density lipoprotein, a marker of systemic oxidative stress, was inversely related to niacin intake (r = -0.23, P < 0.05) and was lower in subjects with above- vs. below-average niacin intake (48 ± 2 vs. 57 ± 2 mg/dl, P < 0.01). Intravenous infusion of the antioxidant vitamin C improved brachial FMD in subjects with below-average niacin intake (P < 0.001, n = 33), but not above-average (P > 0.05, n = 20). In endothelial cells sampled from the brachial artery of a subgroup, dietary niacin intake was inversely related to nitrotyrosine, a marker of peroxynitrite-mediated oxidative damage (r = -0.30, P < 0.05, n = 55), and expression of the prooxidant enzyme, NADPH oxidase (r = -0.44, P < 0.01, n = 37), and these markers were lower in subjects with above- vs. below-average niacin intake [nitrotyrosine: 0.39 ± 0.05 vs. 0.56 ± 0.07; NADPH oxidase: 0.38 ± 0.05 vs. 0.53 ± 0.05 (ratio to human umbilical vein endothelial cell control), both P < 0.05]. Our findings support the hypothesis that higher dietary niacin intake is associated with greater vascular endothelial function related to lower systemic and vascular oxidative stress among healthy middle-aged and older adults.

Keywords: NADPH oxidase; flow-mediated dilation; oxidized low-density lipoprotein.

Fig. 1.

A and C: relation between dietary niacin intake and flow-mediated dilation (FMD) [percent change (%Δ; A), absolute change (mmΔ; C)]. B and D: differences in FMD (%Δ; B, mmΔ; D) between individuals with below- (<22 mg/day, n = 76) and above-average (≥22 mg/day, n = 51) dietary niacin intake. *P < 0.05 vs. low-niacin group.

Fig. 2.

A: relation between dietary niacin intake and circulating oxidized low-density lipoprotein (LDL). B: differences in oxidized LDL between individuals with below- (<22 mg/day, n = 65) and above-average (≥22 mg/day, n = 38) dietary niacin intake. †P < 0.01 vs. low-niacin group.

Fig. 3.

FMD (%Δ) following intravenous infusion of saline and vitamin C (Vit C) in a subset of subjects with below- (<22 mg/day; n = 33) and above-average (≥22 mg/day; n = 20) dietary niacin intake. NS, nonsignificant. ‡P < 0.001 vs. saline condition.

Fig. 4.

A and B: relation between dietary niacin intake and arterial endothelial nitrotyrosine abundance (A) and NADPH oxidase protein expression (B). Representative immunofluorescent images are displayed below each graph. C and D: differences in nitrotyrosine abundance (C) and NADPH oxidase expression (D) between individuals with below- (<22 mg/day; n = 36 and n = 29, respectively) and above-average (≥22 mg/day; n = 19 and n = 8, respectively) dietary niacin intake. Values are expressed as human endothelial cell intensity relative to human umbilical vein endothelial cell intensity. *P < 0.05 vs. low-niacin group.