Introduction
The metabolic processes that occur within our body lead to constant pH changes through a continuous succession of intake-elimination of “acids” and “bases” that alter the concentration of the hydrogen ion (H +), thus changing the pH of the body that must cope with these variations and maintain the physiological pH (pH 7.38-7.44). The metabolism of carbohydrates and fats produces 15,000 mmol of CO2 per day (volatile or respiratory acidosis), while protein metabolism leads to the formation of sulfuric and phosphoric acid (non-volatile acidosis). Therefore, the body has some mechanisms to put in place to maintain the acid-base homeostasis:
Acidosis
Acidosis is a functional alteration due to an excess of hydrogen ions (H+) in the extracellular fluids with a consequent decrease in the buffer reserve; this brings about a change in all the metabolic processes of the cells, as it is necessary - for their proper functioning - to maintain a perfect balance and ratio between the production and excretion of acid and alkaline substances. The main organs involved in this process are the kidney and the lungs. Respiratory acidosis occurs when there is an increase in carbonic acid in the blood, as a result of reduced pulmonary CO2 elimination due to lower ventilation; non-volatile acidosis occurs when there is an increase in the production of acid substances by the body that are released into the extracellular environment (catabolites - see ECW, ECMatrix - BIA-ACC).
Respiratory or volatile acidosis
The cellular metabolic activity leads to the production of carbon dioxide (CO2), that spreads from the cells to the interstitial spaces and, from there, into the bloodstream.
| CO2 + H2O | ⇔ | H2CO3 | ⇔ | H+ + HCO3- |
| Lung | Kidney |
Carbon dioxide flows into the red blood cells and, through the carbonic anhydrase, produces H2CO3, which is in turn split into hydrogen ions (H+) and bicarbonate ions (HCO3-); dissociated hydrogen ions are buffered by haemoglobin and bicarbonates are transported into the plasma. In the lungs, the whole sequence is repeated in reverse so that carbon dioxide is produced again and released into the alveolar air. Volatile acidosis is due to impaired lung ventilation, that can be caused by the following factors: restricted lung expansion (sedentary lifestyle, low aerobic activity and HIIT, inadequate breathing technique, overweight and obesity), airway obstruction (obstructive pulmonary disease), gas exchange disorders (pneumonia, pulmonary oedema), inhibition of the respiratory centre (opiates, barbiturates, anaesthetics), neuromuscular disorders (e.g. multiple sclerosis), neurovegetative dysautonomia (alterations or disorders of the autonomic nervous system - PPG Stress Flow).
Non-volatile acidosis
Non-volatile (or fixed) acids are substances produced in small quantities by the catabolism of amino acids; once produced, they remain in solution until they are excreted by the kidneys. The most important ones are sulphuric acid (H2SO4) , deriving from the oxidation of sulphur contained in sulphur amino acids (methionine and cysteine), and phosphoric acid (H3PO4), resulting from the hydrolysis of salts and phosphates introduced with food. Non-volatile acidosis implies an increase in the production of fixed acids due to metabolic deviations: intense exercise, lipoperoxidation, prolonged fasting, a diet that favours “acid” food such as proteins and carbohydrates (positive PRAL diet), fever, alcoholism, diabetes, ketosis, shock (see also Psychophysical stress, free radicals and antioxidants).
Mixed acidosis
The change in pH affects both volatile and non-volatile acids.
Buffer systems
The addition of acid or basic substances, even in small doses, to a solution leads to a very sharp change in pH. However, if this addition takes place in a solution with a buffer system, the change in pH is minimal. This is because buffer systems are compounds that can limit, within very narrow ranges, the changes in pH by adding small quantities of strong acids or bases. For example, the addition of 0.01 moles of hydrochloric acid (a fraction of a gram) to a litre of water induces a change in pH from 7 to 2, whereas the addition of the same amount of acid to a litre of buffer solution brings about an almost negligible change in pH.
Non-volatile acidosis is due to the presence of acid catabolites that dissociate and release hydrogen ions into the body fluids; these ions are captured by the following buffer systems:
– Bicarbonate/carbonic acid system
In the presence of sulphuric acids, this type of buffer releases hydrogen ions and leads to the formation of water, carbon dioxide and non-volatile acid salt, according to the following reaction:
| H2SO4 + 2NaHCO3 | → | Na2SO4 + 2H2O + CO2 |
| Sulphuric acid | Sodium sulphate |
This system maintains physiological pH values by regulating carbon dioxide pressure through lung ventilation, the excretion of hydrogen ions and the reabsorption of bicarbonate ions in the kidney.
– Phosphate system
| 2Na2HPO4 + H2CO3 | → | 2NaH2PO4 + 2NaHCO3 |
| Monosodium phosphate | Disodium phosphate |
In the phosphate buffer system, the monophosphate ion binds the hydrogen ion when it comes into contact with it in the extracellular environment, and transforms into bisphosphate ion, thus minimising the change in pH.
Solutions to counteract acidosis
As mentioned, the body’s respiratory and renal function and the buffer systems interact to control the pH of body fluids very precisely. When buffers are saturated or altered, or there is respiratory or renal damage, the pH will exceed these limits, leading to the onset of symptoms of acidosis. Temporary pH fluctuations are common and, in most cases, they can be quickly recovered, but if the situation underlying the disorder persists, the pH may remain altered. There are many causes that lead to an imbalance in the acid-base system: the most serious ones are disease conditions such as some CNS disorders involving respiratory and circulatory reflexes, but there are others that are part of daily life and can expose us to this condition, such as stress and alcohol, intensive sports activity, smoking, sedentary lifestyle, insufficient liquid intake, prolonged use of medication, an excess of acidifying food such as meat, cheese and salami, or an insufficient intake of alkalising foods (fruit and vegetables); see PRAL - Potential Renal Acid Load - table.
One of the first solutions, in the case of mild acidosis, is a correct diet, which includes the intake of adequate amounts of fruit and vegetables (basic food). In recent years, a positive relationship has been shown between a high consumption of fruit and vegetables and bone health indices: various diseases can be prevented or their progression stopped through the body’s alkalinity. Fruit and vegetable intake is key because these food groups are oxidised during digestion and release carbonic acid, which dissociates to form carbonates (e.g. sodium carbonate) (see Glycaemic Load - maximum PRAL value Table), i.e. buffering elements – unlike proteins and carbohydrates which form acidic substances. However, contemporary diet is rich in carbohydrates and sodium and low in fruit and vegetables, fibre, magnesium and potassium, and also contains excessive amounts of animal-derived products. This results in the production of non-metabolizable anions, the extent of which increases progressively with age due to the physiological decline in kidney function; hence, supplementation with buffering substances becomes appropriate. Counteracting acidosis is important because of the conditions it can cause: chronic fatigue, sleep disorders, joint pain, increased susceptibility to allergies, frequent inflammation. But perhaps the most interesting topic involving the acid-base balance is osteoporosis: bone tissue plays a fundamental role in balancing the body pH, and is in itself a buffer system against acidosis; acidosis conditions are associated with bone demineralisation (reduced Bbuffer, T-Score - BIA-ACC), hypercalciuria and negative calcium balance. In the body, if there are enough bases to buffer the production of acidic metabolic waste, everything works perfectly, but if this does not occur, the body has to resort to its reserves which normally have other functions. This is the case, for example, of phosphates and carbonates in the bones, which have a structural function. Drawing on this source leads to decalcification, which in turn can obviously lead to increased bone fragility and hypercalcemia. From a therapeutic viewpoint, therefore, in order to cope with such a situation it is essential to take proper supplementation with phosphate and bicarbonate buffer systems: restoring the pH is a strategic priority compared to calcium replenishment, considering that calcium may already have excessive plasma concentrations due to progressive bone demineralisation.
Benefits of the buffer systems
The effectiveness of buffer substances has been proven by scientific literature, that has analysed the benefits of such substances in various fields, from sport to diseases such as cancer.
Sport: lthe intake of sodium bicarbonate has been shown to be beneficial, especially in terms of improved performance, in particular in short-duration, high-intensity sports (boxing, swimming). Benefits are seen both with acute intake (half an hour before activity) and continuous use (better results than acute intake).
Gastrointestinal system:carbonates (also known as antacids) have been used for disorders such as non-ulcer dyspepsia, minor episodes of heartburn (gastro-oesophageal, reflux disease), stress gastritis and gastro-oesophageal reflux, duodenal and gastric ulcers. Their effect on the stomach is due to the partial neutralisation of gastric hydrochloric acid and inhibition of the proteolytic enzyme, pepsin.
Oncology: the tumour microenvironment (extracellular space) is an acidic zone due to over-regulated glycolysis and reduced blood perfusion; there is growing evidence that extracellular acidity increases the invasiveness and metastatic capacity of tumour cells; moreover, this acidity makes these cells relatively resistant to chemotherapeutic drugs and may prevent immune rejection. Studies have shown that increasing extracellular pH has been able to improve the therapeutic efficacy associated with a reduction in the metastatic process and an improved response to certain cytotoxic agents.
Degenerative skeletal diseases: oral administration of potassium bicarbonate, at a dose sufficient to neutralise endogenous acid, improves calcium and phosphorous balance, reduces bone resorption, increases the rate of bone formation as well as the amount of bone calcium (important both in terms of prevention and treatment of osteoporosis). Confirming the positive action of bicarbonates, several studies have reported a reduction in bone resorption after the introduction of bicarbonate (or following a high negative PRAL diet): oral administration of potassium bicarbonate improves calcium and phosphorus balance, reduces bone resorption and increases the rate of bone formation, while the intake of sodium bicarbonate alkalinises urine and reduces the increased urinary calcium excretion, which occurs under acidosis, resulting in a positive net calcium balance: mineral-based and protein-based buffer systems.
Author: Dario Boschiero - Date: 07/01/2021
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