Oral Temperature and pH Influence Dietary Nitrate Metabolism in Healthy Adults

Abstract

This study tested the hypothesis that the increases in salivary and plasma [NO2−] after dietary NO3− supplementation would be greater when oral temperature and pH were independently elevated, and increased further when oral temperature and pH were elevated concurrently. Seven healthy males (mean ± SD, age 23 ± 4 years) ingested 70 mL of beetroot juice concentrate (BR, which provided ~6.2 mmol NO3−) during six separate laboratory visits. In a randomised crossover experimental design, salivary and plasma [NO3−] and [NO2−] were assessed at a neutral oral pH with a low (TLo-pHNorm), intermediate (TMid-pHNorm), and high (THi-pHNorm) oral temperature, and when the oral pH was increased at a low (TLo-pHHi), intermediate (TMid-pHHi), and high (THi-pHHi) oral temperature. Compared with the TMid-pHNorm condition (976 ± 388 µM), the mean salivary [NO2−] 1–3 h post BR ingestion was higher in the TMid-pHHi (1855 ± 423 µM), THi-pHNorm (1371 ± 653 µM), THi-pHHi (1792 ± 741 µM), TLo-pHNorm (1495 ± 502 µM), and TLo-pHHi (2013 ± 662 µM) conditions, with salivary [NO2−] also higher at a given oral temperature when the oral pH was increased (p < 0.05). Plasma [NO2−] was higher 3 h post BR ingestion in the TMid-pHHi, THi-pHHi, and TLo-pHHi conditions, but not the TLo-pHNorm and THi-pHNorm conditions, compared with TMid-pHNorm (p < 0.05). Therefore, despite ingesting the same NO3− dose, the increases in salivary [NO2−] varied depending on the temperature and pH of the oral cavity, while the plasma [NO2−] increased independently of oral temperature, but to a greater extent at a higher oral pH.

Influence of acute dietary nitrate supplementation timing on nitrate metabolism, central and peripheral blood pressure and exercise tolerance in young men

“…Salivary and plasma [NO 3 − ] and [NO 2 − ] were not different between pre-supplementation baseline measures during the morning, afternoon, and evening experimental testing sessions. Consistent with previous research (Bailey et al 2016 ; Cocksedge et al 2023 ; Burleigh et al 2018 ; Woessner et al 2016 ), both salivary and plasma [NO 3 − ] and [NO 2 − ] increased following the acute ingestion of BR in the present study. However, contrary to the experimental hypothesis, the increases in salivary and plasma [NO 3 − ] and [NO 2 − ] after BR supplementation were consistent across the morning, afternoon, and evening.…”

“…In addition to SFR, salivary pH can impact oral NO 3 − reduction. Specifically, increasing salivary pH after NO 3 − supplementation has been reported to increase salivary and plasma [NO 2 − ] (Cocksedge et al 2023 ). Since both unstimulated SFR (Dawes 1975 , 1972 ) and salivary pH (Choi et al 2017 ; Ferguson and Fort 1974 ) exhibit circadian rhythms, with an acrophase in the afternoon, oral NO 3 − reduction and the resultant increases in salivary and plasma [NO 2 − ] after NO 3 − supplementation may be greatest in the afternoon.…”

The Cardioprotective Role of Nitrate-Rich Vegetables

“…Recently, Cocksedge et al [ 34 ] reported that independently increasing or lowering oral temperature or increasing oral pH significantly increased mean salivary NO 2 − after NO 3 − supplementation in healthy adults. In this experiment, seven healthy men consumed 70 mL/day of beetroot juice (which has about 6.2 nM NO 3 − ) during six separate laboratory visits.…”

“…Fresh beetroot fresh juice is most commonly used for nitrate supplementation, but it has a lower concentration compared to other beetroot products ( Table 2 ). Nevertheless, various studies have demonstrated a significant increase in nitrite levels (a marker of NO) in plasma after intake of beetroot juice [ 23 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ].…”

“…Fresh beetroot fresh juice is most commonly used for nitrate supplementation, but it has a lower concentration compared to other beetroot products (Table 2). Nevertheless, various studies have demonstrated a significant increase in nitrite levels (a marker of NO) in plasma after intake of beetroot juice [23,[28][29][30][31][32][33][34][35][36][37][38][39]. The stability of NO3 − in vegetables and their food products is important when considering their functional activity.…”