Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Dietary inorganic nitrate: role in exercise physiology, cardiovascular and metabolic regulation
Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences. (Karolinska Institutet, Inst för fysiologi och farmakologi / Dept of Physiology and Pharmacology)ORCID iD: 0000-0002-1343-8656
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nitric oxide (NO) is a ubiquitous signaling molecule with a vast number of tasks in the body, including regulation of cardiovascular and metabolic function. A decreased bioavailability of NO is a central event in disorders such as hypertension and metabolic syndrome. NO is also important in the regulation of blood flow and metabolism during exercise. The production of NO has previously been thought to be under the exclusive control of the nitric oxide synthases (NOS) but this view is now being seriously challenged. Recent lines of research suggest the existence of an NO-synthase independent pathway in which the supposedly inert NO oxidation products nitrate (NO3-) and nitrite (NO2-) can be reduced back to NO in blood and tissues. An important additional source of nitrate is our everyday diet and certain vegetables are particularly rich in this anion. In this thesis the possibility that dietary derived nitrate is metabolized in vivo to form reactive nitrogen oxides with NO-like bioactivity has been explored. It is shown that nitrate in amounts easily achieved via the diet, increases the systemic levels of nitrite and reduces blood pressure in healthy humans. Moreover, nitrate reduces whole body oxygen cost during submaximal and maximal exercise; a surprising effect involving improvement in mitochondrial efficiency and reduced expression of specific mitochondrial proteins regulating proton conductance. Alterations in the mitochondrial affinity for oxygen can explain this reduction in both submaximal and maximal oxygen consumption and predicts basal metabolic rate in humans. Finally, in mice lacking endothelial NO synthase, dietary supplementation with nitrate could reverse several features of the metabolic syndrome that develop in these animals. These studies demonstrate that dietary nitrate can fuel a nitrate-nitrite-NO pathway with important implications for cardiovascular and metabolic functions in health and disease.

Place, publisher, year, edition, pages
Solna: Karolinska Institutet , 2011.
National Category
Medical and Health Sciences
Research subject
Medicine/Technology
Identifiers
URN: urn:nbn:se:gih:diva-2079ISBN: 978-91-7457-397-8 (print)OAI: oai:DiVA.org:gih-2079DiVA: diva2:474305
Public defence
2011-06-17, Aulan Farmakologen, Nanna Svartz väg 2, Solna, 09:00 (English)
Opponent
Supervisors
Note
Avhandling vid Karolinska Institutet och Gymnastik- och idrottshögskolan, GIHAvailable from: 2012-01-09 Created: 2012-01-09 Last updated: 2016-08-08Bibliographically approved
List of papers
1. Effects of dietary nitrate on blood pressure in healthy volunteers
Open this publication in new window or tab >>Effects of dietary nitrate on blood pressure in healthy volunteers
Show others...
2006 (English)In: New England Journal of Medicine, ISSN 0028-4793, Vol. 28, no 355(26), 2792-3 p.Article in journal (Refereed) Published
Abstract [en]

To the Editor:

Nitric oxide, generated by nitric oxide synthase, is a key regulator of vascular integrity. This system is dysfunctional in many cardiovascular disorders, including hypertension. A fundamentally different pathway for the generation of nitric oxide was recently described in which the anions nitrate (NO3 ) and nitrite (NO2 ) are converted into nitric oxide and other bioactive nitrogen oxides.1-3 Nitrate is abundant in our diet, and particularly high levels are found in many vegetables.3

We examined the effect of 3-day dietary supplementation with either sodium nitrate (at a dose of 0.1 mmol per kilogram of body weight per day) or placebo (sodium chloride, at a dose of 0.1 mmol per kilogram per day) on blood pressure in 17 physically active, healthy volunteers, none of whom smoked (15 men and 2 women; mean age, 24 years). The study had a randomized, double-blind, crossover design with two different treatment periods during which the subjects received either nitrate or placebo; the treatment periods were separated by a washout period of at least 10 days. The compounds were dissolved in water and could not be distinguished by taste or appearance. During the two treatment periods, the subjects were instructed to avoid all foods with a moderate or high nitrate content.3

Systolic blood pressure Effects of 3-Day Dietary Supplementation with Inorganic Nitrate or Placebo on Systolic (Panel A) and Diastolic (Panel B) Blood Pressure in 17 Healthy Volunteers.) and pulse rate did not change significantly after nitrate supplementation, as compared with placebo supplementation. However, the diastolic blood pressure was on average 3.7 mm Hg lower after nitrate supplementation than after placebo supplementation (P<0.02) (Figure 1B), and the mean arterial pressure was 3.2 mm Hg lower (P<0.03). Plasma nitrate levels were higher after nitrate ingestion than after placebo ingestion (mean [±SD], 178±51 and 26±11 μM, respectively; P<0.001), as were plasma nitrite levels (219±105 and 138±38 nM, respectively; P<0.01).

The daily nitrate dose used in the study corresponds to the amount normally found in 150 to 250 g of a nitrate-rich vegetable such as spinach, beetroot, or lettuce. It is clear from earlier studies, such as the Dietary Approaches to Stop Hypertension (DASH) trial, that a diet rich in fruits and vegetables can reduce blood pressure,4,5 but attempts to modify single nutrients have been inconsistent. Therefore, it has been argued that the effect of any individual nutrient is too small to detect in trials. In our study, reduced blood pressure was associated with nitrate supplementation alone; this effect was evident in young normotensive subjects. In fact, it was similar to that seen in the healthy control group in the DASH study.4 The exact mechanism behind the blood-pressure–lowering effect of nitrate needs to be clarified in future studies.

We conclude that short-term dietary supplementation with inorganic nitrate reduces diastolic blood pressure in healthy young volunteers.

National Category
Physiology
Research subject
Medicine/Technology
Identifiers
urn:nbn:se:gih:diva-303 (URN)10.1056/NEJMc062800 (DOI)17192551 (PubMedID)
Available from: 2007-10-12 Created: 2007-10-12 Last updated: 2017-03-31Bibliographically approved
2. Effects of dietary nitrate on oxygen cost during exercise
Open this publication in new window or tab >>Effects of dietary nitrate on oxygen cost during exercise
2007 (English)In: Acta Physiologica, ISSN 1748-1708, E-ISSN 1748-1716, Vol. 191, no 1, 59-66 p.Article in journal (Refereed) Published
Abstract [en]

AIM: Nitric oxide (NO), synthesized from l-arginine by NO synthases, plays a role in adaptation to physical exercise by modulating blood flow, muscular contraction and glucose uptake and in the control of cellular respiration. Recent studies show that NO can be formed in vivo also from the reduction of inorganic nitrate (NO(3) (-)) and nitrite (NO(2) (-)). The diet constitutes a major source of nitrate, and vegetables are particularly rich in this anion. The aim of this study was to investigate if dietary nitrate had any effect on metabolic and circulatory parameters during exercise. METHOD: In a randomized double-blind placebo-controlled crossover study, we tested the effect of dietary nitrate on physiological and metabolic parameters during exercise. Nine healthy young well-trained men performed submaximal and maximal work tests on a cycle ergometer after two separate 3-day periods of dietary supplementation with sodium nitrate (0.1 mmol kg(-1) day-1) or an equal amount of sodium chloride (placebo). RESULTS: The oxygen cost at submaximal exercise was reduced after nitrate supplementation compared with placebo. On an average Vo(2) decreased from 2.98 +/- 0.57 during CON to 2.82 +/- 0.58 L min(-1) during NIT (P < 0.02) over the four lowest submaximal work rates. Gross efficiency increased from 19.7 +/- 1.6 during CON to 21.1 +/- 1.3% during NIT (P < 0.01) over the four lowest work rates. There was no difference in heart rate, lactate [Hla], ventilation (VE), VE/Vo(2) or respiratory exchange ratio between nitrate and placebo during any of the submaximal work rates. CONCLUSION: We conclude that dietary nitrate supplementation, in an amount achievable through a diet rich in vegetables, results in a lower oxygen demand during submaximal work. This highly surprising effect occurred without an accompanying increase in lactate concentration, indicating that the energy production had become more efficient. The mechanism of action needs to be clarified but a likely first step is the in vivo reduction of dietary nitrate into bioactive nitrogen oxides including nitrite and NO.

National Category
Physiology
Identifiers
urn:nbn:se:gih:diva-302 (URN)
Available from: 2007-10-12 Created: 2007-10-12 Last updated: 2017-03-31Bibliographically approved
3. Dietary nitrate reduces maximal oxygen consumption while maintaining work performance in maximal exercise.
Open this publication in new window or tab >>Dietary nitrate reduces maximal oxygen consumption while maintaining work performance in maximal exercise.
2010 (English)In: Free Radical Biology & Medicine, ISSN 0891-5849, E-ISSN 1873-4596, Vol. 48, no 2, 342-7 p.Article in journal (Refereed) Published
Abstract [en]

The anion nitrate-abundant in our diet-has recently emerged as a major pool of nitric oxide (NO) synthase-independent NO production. Nitrate is reduced stepwise in vivo to nitrite and then NO and possibly other bioactive nitrogen oxides. This reductive pathway is enhanced during low oxygen tension and acidosis. A recent study shows a reduction in oxygen consumption during submaximal exercise attributable to dietary nitrate. We went on to study the effects of dietary nitrate on various physiological and biochemical parameters during maximal exercise. Nine healthy, nonsmoking volunteers (age 30+/-2.3 years, VO(2max) 3.72+/-0.33 L/min) participated in this study, which had a randomized, double-blind crossover design. Subjects received dietary supplementation with sodium nitrate (0.1 mmol/kg/day) or placebo (NaCl) for 2 days before the test. This dose corresponds to the amount found in 100-300 g of a nitrate-rich vegetable such as spinach or beetroot. The maximal exercise tests consisted of an incremental exercise to exhaustion with combined arm and leg cranking on two separate ergometers. Dietary nitrate reduced VO(2max) from 3.72+/-0.33 to 3.62+/-0.31 L/min, P<0.05. Despite the reduction in VO(2max) the time to exhaustion trended to an increase after nitrate supplementation (524+/-31 vs 563+/-30 s, P=0.13). There was a correlation between the change in time to exhaustion and the change in VO(2max) (R(2)=0.47, P=0.04). A moderate dietary dose of nitrate significantly reduces VO(2max) during maximal exercise using a large active muscle mass. This reduction occurred with a trend toward increased time to exhaustion implying that two separate mechanisms are involved: one that reduces VO(2max) and another that improves the energetic function of the working muscles.

National Category
Physiology
Research subject
Medicine/Technology
Identifiers
urn:nbn:se:gih:diva-1429 (URN)10.1016/j.freeradbiomed.2009.11.006 (DOI)19913611 (PubMedID)
Available from: 2010-11-02 Created: 2010-11-02 Last updated: 2017-03-31Bibliographically approved
4. Dietary inorganic nitrate reverses features of metabolic syndrome in endothelial nitric oxide synthase-deficient mice.
Open this publication in new window or tab >>Dietary inorganic nitrate reverses features of metabolic syndrome in endothelial nitric oxide synthase-deficient mice.
Show others...
2010 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 41, 17716-20 p.Article in journal (Refereed) Published
Abstract [en]

The metabolic syndrome is a clustering of risk factors of metabolic origin that increase the risk for cardiovascular disease and type 2 diabetes. A proposed central event in metabolic syndrome is a decrease in the amount of bioavailable nitric oxide (NO) from endothelial NO synthase (eNOS). Recently, an alternative pathway for NO formation in mammals was described where inorganic nitrate, a supposedly inert NO oxidation product and unwanted dietary constituent, is serially reduced to nitrite and then NO and other bioactive nitrogen oxides. Here we show that several features of metabolic syndrome that develop in eNOS-deficient mice can be reversed by dietary supplementation with sodium nitrate, in amounts similar to those derived from eNOS under normal conditions. In humans, this dose corresponds to a rich intake of vegetables, the dominant dietary nitrate source. Nitrate administration increased tissue and plasma levels of bioactive nitrogen oxides. Moreover, chronic nitrate treatment reduced visceral fat accumulation and circulating levels of triglycerides and reversed the prediabetic phenotype in these animals. In rats, chronic nitrate treatment reduced blood pressure and this effect was also present during NOS inhibition. Our results show that dietary nitrate fuels a nitrate-nitrite-NO pathway that can partly compensate for disturbances in endogenous NO generation from eNOS. These findings may have implications for novel nutrition-based preventive and therapeutic strategies against cardiovascular disease and type 2 diabetes.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:gih:diva-2080 (URN)10.1073/pnas.1008872107 (DOI)20876122 (PubMedID)
Available from: 2012-01-09 Created: 2012-01-09 Last updated: 2016-08-08Bibliographically approved
5. Dietary inorganic nitrate improves mitochondrial efficiency in humans.
Open this publication in new window or tab >>Dietary inorganic nitrate improves mitochondrial efficiency in humans.
Show others...
2011 (English)In: Cell Metabolism, ISSN 1550-4131, Vol. 13, no 2, 149-159 p.Article in journal (Refereed) Published
Abstract [en]

Nitrate, an inorganic anion abundant in vegetables, is converted in vivo to bioactive nitrogen oxides including NO. We recently demonstrated that dietary nitrate reduces oxygen cost during physical exercise, but the mechanism remains unknown. In a double-blind crossover trial we studied the effects of a dietary intervention with inorganic nitrate on basal mitochondrial function and whole-body oxygen consumption in healthy volunteers. Skeletal muscle mitochondria harvested after nitrate supplementation displayed an improvement in oxidative phosphorylation efficiency (P/O ratio) and a decrease in state 4 respiration with and without atractyloside and respiration without adenylates. The improved mitochondrial P/O ratio correlated to the reduction in oxygen cost during exercise. Mechanistically, nitrate reduced the expression of ATP/ADP translocase, a protein involved in proton conductance. We conclude that dietary nitrate has profound effects on basal mitochondrial function. These findings may have implications for exercise physiology- and lifestyle-related disorders that involve dysfunctional mitochondria.

National Category
Physiology
Research subject
Medicine/Technology
Identifiers
urn:nbn:se:gih:diva-1805 (URN)http://dx.doi.org/10.1016/j.cmet.2011.01.004 (DOI)21284982 (PubMedID)
Available from: 2011-05-06 Created: 2011-05-06 Last updated: 2017-03-31Bibliographically approved
6. Mitochondrial oxygen affinity predicts basal metabolic rate in humans
Open this publication in new window or tab >>Mitochondrial oxygen affinity predicts basal metabolic rate in humans
2011 (English)In: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 25, no 8, 2843-52 p.Article in journal (Refereed) Published
Abstract [en]

The basal metabolic rate (BMR) is referred to as the minimal rate of metabolism required to support basic body functions. It is well known that individual BMR varies greatly, even when correcting for body weight, fat content, and thyroid hormone levels, but the mechanistic determinants of this phenomenon remain unknown. Here, we show in humans that mass-related BMR correlates strongly to the mitochondrial oxygen affinity (p50(mito); R(2)=0.66, P=0.0004) measured in isolated skeletal muscle mitochondria. A similar relationship was found for oxygen affinity and efficiency during constant-load submaximal exercise (R(2)=0.46, P=0.007). In contrast, BMR did not correlate to overall mitochondrial density or to proton leak. Mechanistically, part of the p50(mito) seems to be controlled by the excess of cytochrome c oxidase (COX) protein and activity relative to other mitochondrial proteins. This is illustrated by the 5-fold increase in p50(mito) after partial cyanide inhibition of COX at doses that do not affect maximal mitochondrial electron flux through the ETS. These data suggest that the interindividual variation in BMR in humans is primarily explained by differences in mitochondrial oxygen affinity. The implications of these findings are discussed in terms of a trade-off between aerobic efficiency and power.

National Category
Medical and Health Sciences
Research subject
Medicine/Technology
Identifiers
urn:nbn:se:gih:diva-1913 (URN)21576503 (PubMedID)
Note
At the time of Filip Larsens dissertation the article was accepted, not yet published.Available from: 2011-10-14 Created: 2011-10-14 Last updated: 2017-03-31Bibliographically approved

Open Access in DiVA

No full text

Other links

Länk till avhandlingen hos Karolinska Institutet

Search in DiVA

By author/editor
Larsen, Filip J.
By organisation
Department of Sport and Health Sciences
Medical and Health Sciences

Search outside of DiVA

GoogleGoogle Scholar

Total: 337 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf