Abstract
This study was conducted to investigate whether regular dietary intake of l-arginine is associated with serum nitrate + nitrite (NOx). In this cross-sectional study, 2771 men and women, who had participated in the third examination of the Tehran Lipid and Glucose Study (2006–2008), were recruited. Demographics, anthropometrics and biochemical variables were evaluated. Dietary data were collected using a validated 168-food item semi-quantitative food frequency questionnaire and dietary intake of l-arginine was calculated. To determine any association between dietary l-arginine and serum NOx, linear regression models with adjustment for potential confounders were used. Mean age of participants (39.2% men) was 45.9 ± 15.9 years. After adjustment for all potential confounding variables, a significant positive association was observed between l-arginine intake and serum NOx concentrations in the fourth quartile of l-arginine (β = 6.63, 95% CI = 4.14, 9.12, p for trend = 0.001), an association stronger in women. Further analysis, stratified by age, body mass index and hypertension status categories, showed a greater association in middle-aged and older adults (β = 9.12, 95% CI = 3.99, 13.6 and β = 12.1, 95% CI = 6.48, 17.7, respectively). l-arginine intakes were also strongly associated with serum NOx levels in overweight and obese subjects in the upper quartile (β = 10.7, 95% CI = 5.43, 16.0 and β = 11.0, 95% CI = 4.29, 17.5); a greater association was also observed between l-arginine intakes and serum NOx in non-hypertensive (HTN) compared to HTN subjects (β = 2.65, 95% CI = 2.1–3.2 vs. β = 1.25, 95% CI = −1.64–4.15). Dietary l-arginine intakes were associated to serum NOx and this association may be affected by sex, age, body mass index, and hypertension status.
Highlights
L -arginine is a conditionally essential amino acid and its deficiency has been reported to be related to a variety of inflammatory and oxidative processes leading to metabolic disorders and cardiovascular diseases [1,2,3]
Basal nitric oxide (NO) synthesis rate in healthy subjects has been estimated to be in the range of 13–65 μmol/h; plasma L-arginine supplies 54% of the substrate used for whole daily NO synthesis [14], and contribution of dietary L-arginine intake in the daily basal NO synthesis was reported at approximately 2.7%–5.7% (1.1–2.3 μmol/h during the 8 h following a low-and high-arginine diet, respectively) [15,16]
A univariate analysis was performed for each potential confounder including age, medication usage, smoking, obesity, diabetes, hypertension, serum creatinine as well as the main nitrate–nitrite containing foods including high- and medium-nitrate containing vegetables, grains and processed meats; variables with PE < 0.2 in the univariate analysis were selected for the multivariable models; PE (p value for entry) determines which variables should be included in the final multivariable model
Summary
L -arginine is a conditionally essential amino acid and its deficiency has been reported to be related to a variety of inflammatory and oxidative processes leading to metabolic disorders and cardiovascular diseases [1,2,3]. L-Arginine is involved in production of nitric oxide (NO), an important signaling molecule in biological pathways, as the substrate of NO synthase (NOS) enzymes family [5,6]. Basal NO synthesis rate in healthy subjects has been estimated to be in the range of 13–65 μmol/h; plasma L-arginine supplies 54% of the substrate used for whole daily NO synthesis [14], and contribution of dietary L-arginine intake in the daily basal NO synthesis was reported at approximately 2.7%–5.7% (1.1–2.3 μmol/h during the 8 h following a low-and high-arginine diet, respectively) [15,16]. Direct utilization of dietary L-arginine in NO synthesis seems to be low, and reduced L-arginine intake may limit NO production due to a large dependence of intracellular
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