HMS4602: SPORTS SUPPLEMENTS AND
ERGOGENIC AIDS
Faculty of Health, Medicine and Life Sciences
Human Movement Sciences; Sports Nutrition
2020-2021
,HMS4602: SPORTS SUPPLEMENTS AND ERGOGENIC AIDS
NITRATE
WHAT IS NITRATE
Nitrate (NO3-) serves as a precursor for Nitrite (NO 2-) and Nitric Oxide (NO) (the active compound). NO 3- can be reduced to NO2- in
the human mouth and, further, under hypoxia and/or low pH, to NO. NO is a gaseous signaling molecule that is produced
continuously to enable or facilitate:
- Neurotransmission
- Vasodilation
- Angiogenesis
- Cellular respiration
- Mitochondrial biogenesis
- Muscular contraction
The nitrate-nitrite-NO pathway represents an alternative and differently regulated system for NO generation that operates in
parallel to the classical L-arginine-NOS-NO pathway. Several researchers have lined out that the nitrate-nitrate-NO pathway is
involved in regulation of blood flow, blood pressure, cell signaling, glucose homeostasis and tissue responses to hypoxia.
These findings could be of interest in patients with cardiovascular, respiratory or metabolic diseases.
Exogenous and endogenous nitrates
Although inorganic nitrate is present at high levels in beetroot, celery and in green leafy vegetables such as spinach and lettuce,
humans do not only get NO3- from their diet. Nitrate is also generated endogenously by oxidation of nitric oxide (NO) formed
canonically via the L-arginine/NO synthase pathway.
Nitric oxide production via NOS enzymes requires the presence of O 2-. A backup system of NO is located in skeletal muscle
which is used in low PO2 conditions. Local storage of nitrite would minimize the reduction steps required to increase NO
bioavailability.
Nitric oxide can be produced alternatively via the NOS-independent, single-electron reduction of NO 2-, which is obtained via
dietary NO2- and NO3- as well as via oxidation of endogenous NO. A maintenance of NO availability is obtained under
circumstances of low PO2 and low pH.
WHAT IS THE MECHANISM OF NITRATE IN THE BODY?
1) 25% of nitrate is absorbed in the intestine and transported in the blood.
2) When humans eat NO3- rich food, 5-7% of NO3- is converted to NO2- by nitrate reductases in commensal bacteria that reside
in the posterior part of the tongue.
3) Reduced Salivary NO2- is rapidly protonated in the acidic environment of the stomach resulting in the formation of NO and
(in some circumstances) other reactive nitrogen species (RNS) including nitrogen dioxide (NO 2), nitrous acid (HNO2) and
dinitrogen trioxide (N2O3).
4) Approximately 20% of the nitrate (re-)entering the oral cavity through the salivary glands is reduced to nitrite by commensal
bacteria residing on the dorsal part of the tongue. Nitrite is subsequently swallowed, absorbed into the circulation from the
intestines and transported to other parts within the body where further reduction to NO and other nitrogen oxides.
Nitrate supplementation has been shown to decrease diastolic blood pressure.
When the same supplementation protocol was used in participants that performed different exercise intensities, it was
shown that the amount of oxygen needed to perform the same
exercise intensity was lower than when compared to the control
group. This indicates that nitrate supplementation increases the
efficiency of energy production.
, These results were quite promising, therefore a time-to-exhaustion study was performed and the beetroot-supplemented
group showed a 16% increase in time to-exhaustion when compared to the placebo group.
Blood pressure
Nitric oxide induces the activity of cGMP, which leads to smooth muscle relaxation. Smooth muscle is the type of muscle located
in the blood vessels, therefore, if relaxation in these muscles occurs, blood pressure will be lowered. Nitrate supplementation
might therefore be beneficial in high-blood-pressure populations.
Where is NO formed? And stored?
Muscle
Dietary NO3- increases the efficiency of ATP synthesis and/or of skeletal muscle work by increasing the expression of glucose
transporters and/or by raising insulin availability.
Furthermore, NO3- increases the rate of skeletal muscle recovery after exercise in hypoxia, which suggests an increased
maximum rate of oxidative ATP synthesis and lowers the ATP cost of contractile force production.
NO regulates calcium flux via S-nitrosylation of thiols contained in ryranodine receptor (RyR1) Ca 2+ channels. These are activated
only by NO at low physiological PO 2 (10 mm Hg), such that low PO 2 in active muscle increases contractility, and high physiological
PO2 has the opposite effect.
Type 2 (fast twitch) fibers differ in terms of myofibrillar protein content and calcium handling, typically have lower
mitochondrial and capillary density and, therefore, rely relatively more on nonoxidative compared with oxidative pathways of
ATP resynthesis. The article of Jones et al., hypothesizes that Type 2 muscle fibers may be especially targeted by NO 3-
supplementation rests, at least in part, on differences in intramyocyte PO 2.
Type 1 muscle fibers Type 2 muscle fibers
- High capillary density - Low oxygen availability
- High mitochondrial density - Anaerobic energy production
NO2- also modulates cell signaling independently of NO in hypoxia and normoxia. NO 2- activates AMPK in rat aortic smooth
muscle, thus stimulating mitochondrial biogenesis, and increasing coupling efficiency and cellular respiratory control. NO−2
activates PKA in cultured cardiomyocytes, stimulating mitochondrial fusion and again increasing cellular respiratory control NO2-
increases proliferation of muscle and epithelial cells (Totzeck et al., 2014)
Mitochondria
Reactive nitrogen species (ROS) can modify proteins and may thus improve mitochondrial
coupling efficiency in various ways by for instance increasing electron transfer in respiratory
complexes. Some experiments have shown that beetroot juice (containing nitrates) provokes
mitochondrial biogenesis and increases basal cellular respiration without affecting respiratory
capacity and proton leak.
