Influence of iodide ingestion on nitrate metabolism and blood pressure following short-term dietary nitrate supplementation in healthy normotensive adults

Uptake of inorganic nitrate (NO3-) into the salivary circulation is a rate-limiting step for dietary NO3- metabolism in mammals. It has been suggested that salivary NO3- uptake occurs in competition with inorganic iodide (I-). Therefore, this study tested the hypothesis that I- supplementation would interfere with NO3- metabolism and blunt blood pressure reductions after dietary NO3- supplementation. Nine healthy adults (4 male, mean +/- SD, age 20 +/- 1 yr) reported to the laboratory for initial baseline assessment (control) and following six day supplementation periods with 140 mL.day(-1) NO3--rich beetroot juice (8.4 mmol NO3-.day(-1)) and 198 mg potassium gluconate.day(-1) (nitrate), and 140 mL.day(-1) NO3--rich beetroot juice and 450 mu g potassium iodide.day(-1) (nitrate + iodide) in a randomized, cross-over experiment. Salivary [I-] was higher in the nitrate + iodide compared to the control and NIT trials (P < 0.05). Salivary and plasma [NO3-] and [NOT] were higher in the nitrate and nitrate + iodide trials compared to the control trial (P < 0.05). Plasma [NO3-] was higher (474 +/- 127 vs. 438 +/- 117 mu M) and the salivary-plasma [NO3-] ratio was lower (14 +/- 6 vs. 20 +/- 6 mu M), indicative of a lower salivary NO3- uptake, in the nitrate + iodide trial compared to the nitrate trial (P < 0.05). Plasma and salivary [NO3-] were not different between the nitrate and nitrate + iodide trials (P > 0.05). Systolic blood pressure was lower than control (112 +/- 13 mmHg) in the nitrate (106 +/- 13 mmHg) and nitrate + iodide (106 11 mmHg) trials (P < 0.05), with no differences between the nitrate and nitrate + iodide trials (P > 0.05). In conclusion, co-ingesting NO3- and I- perturbed salivary NO3- uptake, but the increase in salivary and plasma [NO3-] and the lowering of blood pressure were similar compared to NO3- ingestion alone. Therefore, increased dietary I- intake, which is recommended in several countries worldwide as an initiative to offset hypothyroidism, does not appear to compromise the blood pressure reduction afforded by increased dietary NO3- intake. (C) 2016 Elsevier Inc. All rights reserved.