Effects of short-term dietary nitrate supplementation on blood pressure, O₂uptake kinetics, and muscle and cognitive function in older adults

Abstract

AM. Effects of shortterm dietary nitrate supplementation on blood pressure, O 2 uptake kinetics, and muscle and cognitive function in older adults. Am J Physiol Regul Integr Comp Physiol 304: R73-R83, 2013. First published November 21, 2012 doi:10.1152/ajpregu.00406.2012 Ϫ ) supplementation has been shown to reduce resting blood pressure and alter the physiological response to exercise in young adults. We investigated whether these effects might also be evident in older adults. In a double-blind, randomized, crossover study, 12 healthy, older (60 -70 yr) adults supplemented their diet for 3 days with either nitrate-rich concentrated beetroot juice (BR; 2 ϫ 70 ml/day, ϳ9.6 mmol/day NO 3 Ϫ ) or a nitrate-depleted beetroot juice placebo (PL; 2 ϫ 70 ml/day, ϳ0.01 mmol/day NO 3 Ϫ ). Before and after the intervention periods, resting blood pressure and plasma [nitrite] were measured, and subjects completed a battery of physiological and cognitive tests. Nitrate supplementation significantly increased plasma [nitrite] and reduced resting systolic (BR: 115 Ϯ 9 vs. PL: 120 Ϯ 6 mmHg; P Ͻ 0.05) and diastolic (BR: 70 Ϯ 5 vs. PL: 73 Ϯ 5 mmHg; P Ͻ 0.05) blood pressure. Nitrate supplementation resulted in a speeding of the V O2 mean response time (BR: 25 Ϯ 7 vs. PL: 28 Ϯ 7 s; P Ͻ 0.05) in the transition from standing rest to treadmill walking, although in contrast to our hypothesis, the O 2 cost of exercise remained unchanged. Functional capacity (6-min walk test), the muscle metabolic response to low-intensity exercise, brain metabolite concentrations, and cognitive function were also not altered. Dietary nitrate supplementation reduced resting blood pressure and improved V O2 kinetics during treadmill walking in healthy older adults but did not improve walking or cognitive performance. These results may have implications for the enhancement of cardiovascular health in older age.nitrate; nitrite; nitric oxide; blood pressure; exercise performance; cognitive performance; O2 uptake kinetics THE BENEFICIAL EFFECTS OF a vegetable-rich diet upon cardiovascular health (27) and longevity (79) have been well described. These positive effects have been attributed, in part, to inorganic nitrate (NO 3 Ϫ ), which is particularly rich in leafy greens and beetroot. The NO 3 Ϫ anion itself is inert, and any biological effects are likely to be the result of its conversion to the nitrite anion (NO 2 Ϫ ) in the mouth via facultative anaerobic bacteria on the surface of the tongue (25). When swallowed, NO 2 Ϫ can be further converted into nitric oxide (NO) (9), but it is clear that some NO 2 Ϫ enters the circulation. The subsequent reduction of NO 2 Ϫ to NO and other reactive nitrogen intermediates is facilitated in hypoxia (11). The production of NO via nitric oxide synthase (NOS) is impaired in hypoxia and, thus, it has been proposed that the NO 3 Ϫ -NO 2 Ϫ -NO pathway represents a complementary system for NO generation across a wide range of redox states (53). NO is an essential physiological signaling molecule with numerous functions in...

Effect of dietary nitrate on blood pressure, endothelial function, and insulin sensitivity in type 2 diabetes

“…Again this used a higher daily dose of 9.6 mmoles of nitrate, with the last supplementation episode 2.5 hours prior to BP measurement in laboratory conditions. 45 The unsupplemented plasma nitrite concentration in the diabetic cohort described in the present study -which had a median value and range of 232 nmol/L (200, 265) -was similar to that in the healthy subjects in Kelly et al's study (248 ± 182 nmol/l; mean ± SD). 45 The study by Sobko et al 46 examined the effect of a traditional Japanese diet.…”

“…45 The unsupplemented plasma nitrite concentration in the diabetic cohort described in the present study -which had a median value and range of 232 nmol/L (200, 265) -was similar to that in the healthy subjects in Kelly et al's study (248 ± 182 nmol/l; mean ± SD). 45 The study by Sobko et al 46 examined the effect of a traditional Japanese diet. The subjects had a mean age of 36 ± 10 years and again no difference was seen in systolic BP.…”

Dietary nitrate supplementation: effects on plasma nitrite and pulmonary O2 uptake dynamics during exercise in hypoxia and normoxia

“…This finding is consistent with a recent study in older individuals, where the V O 2 mean response time was speeded with BR supplementation (32). This may be related to the slower V O 2 kinetics that is typically found in older individuals and the potential to abate this through enhancing muscle O 2 delivery (57), via increasing NO bioavailability.…”

“…Furthermore, the interindividual differences in the V O 2 response to exercise in normoxia evident in the current study, may have also contributed to the lack of statistically significant effects. It may be concluded that BR supplementation can (3,4,14,40,41,62), but does not always (present study, 5,8,32,66), alter the O 2 cost of exercise in normoxia.…”

Improvement in blood pressure after short-term inorganic nitrate supplementation is attenuated in cigarette smokers compared to non-smoking controls

“…Increased dietary NO 3 -intake in the form of NO 3 --rich beetroot [11][12][13] or spinach [14,15] supplementation alone has also been shown to lower resting blood pressure. These findings are consistent with the emerging body of evidence to support improved vascular health following dietary NO 3 -supplementation (4-16 mmol·day -1 ) in younger [11][12][13] and older [16,17] normotensive adults, and in individuals with hypertension [18], peripheral artery disease [19] and heart failure [20]. Therefore, enriching the diet with NO 3 -, at a dose that can be readily achieved by a diet high in vegetables [4,7,9], might represent a practical and cost-effective intervention to lower cardiovascular disease morbidity and mortality.…”