Bone tissue undergoes remodeling throughout life. It is a dynamic balance of simultaneous destruction (resorption) and bone formation. Remodeling allows you to fuse bones and eliminate fragments after fractures. An imbalance in the direction of bone resorption causes osteopenia, which leads to osteoporosis.
Osteoporosis is a bone disease in which the loss of bone mass exceeds its accumulation. The disease is most often manifested in the elderly, characterized by bone fragility and accompanied by fractures.
About 50 years ago, it was hypothesized that a diet high in animal proteins increases the acid load on the body. Bone tissue, decreasing in volume, neutralizes part of the food acid load. Decades of high-acid diets contribute to bone loss in osteoporosis. The proposed idea was that the process of bone resorption could be slowed or stopped by an alkaline diet.
At the same time, in vitro studies were conducted demonstrating the dissolution of bones by acid. In vivo studies on animals and humans have shown that an acid-producing diet resulted in a negative calcium balance and reduced bone volume.
Acid balance of the body
For living systems to maintain balance, the amount of substance at the input must equal the amount of material at the output.
The level of acidity (pH) of the blood reflects the production, buffering, and excretion of both acids and alkalis. In healthy people with normal kidney function, the blood pH ranges from 7.35 to 7.45. The kidneys of such people can remove excess acid even with a high-acid diet.
With age, the body’s ability to maintain a healthy pH level decreases. By the age of 80, it falls to the range lower limit and decreasing of the bicarbonates level in the blood. The most likely cause is kidney function reduction. It is the kidneys, forming bicarbonate, that removes the bulk of non-carbon acid (not H2CO3).
Food acids and alkalis
Biochemical analysis of food revealed the acidic orientation of most of them. However, in addition to acid precursors, fruits and vegetables also contain alkali precursors.
Many studies have attempted to assess the acidic or alkaline effects of various foods on the body. For this purpose, formulas were developed that take into account cations (sodium, potassium, calcium, magnesium) and anions (chloride, sulfate, phosphate). Some methods also involve the production of anions and the factor of ion absorption in the intestine. The use of indicators of acid or alkaline food exposure allows you to exclude the influence of the renal factor on the final value of the evaluated parameter. As a result, it was found that the average modern diet produces about 50 millimoles of acid per day.
Alkaline diet effectiveness in osteoporosis prevention
Proponents of the alkaline diet theory rely on in vitro studies that found that increasing acid levels activates osteoclasts (multi-core cells that destroy bone tissue). Thus, the systematic use of acid precursor products leads to a stable high level of acid in the blood and tissues of the body. This process is aggravated by an age-related decline in the ability of the kidneys to regulate the acid-base balance. Therefore, the diet may be a clinically significant factor in osteoporosis.
In vitro studies have shown that at a pH close to 7.0, the activity of osteoblasts (cells that form new bone) decreases, and the operation of osteoclasts increases. In a more alkaline environment with a pH of about 7.4, the opposite effect was observed: the activity of osteoblasts was maximal, and the activity of osteoclasts significantly decreased. Moreover, it has been noted that at pH < 7.4, osteoblasts do not mineralize the bone's collagen matrix. It was also found that a decrease in systemic pH leads to an increase in the release of calcium from living and dead bones.
Human studies further support this hypothesis.
In one study, 18 postmenopausal women received oral potassium bicarbonate (KHCO3) for 18 days. The dose was sufficient to neutralize endogenous acid (from 71 to 13 mmol per day). The result was an improved balance of calcium and phosphorus – more of these elements entered the body than were excreted in the urine and feces. The positive calcium balance was 56 ± 76 mg per day per 60 kg. The positive phosphorus balance was 47 ± 64 mg. The value of osteocalcin, a marker of bone formation, also increased. In blood serum, this indicator increased from 5.5 ± 2.8 to 6.1 ± 2.8 ng per milliliter. There was a decrease in hydroxyproline, a marker of bone resorption. Its value in the urine decreased from 28.9 ± 12.3 to 26.7 ± 10.8 mg per day.
Another 4-week randomized controlled trial involved 30 young and healthy women with regular calcium intake. One group of participants took alkaline mineral water rich in bicarbonate. Another group is acidic mineral water, rich in calcium. As a result, it turned out that alkaline water leads to a significant decrease in serum parathyroid hormone and C-telopeptide, a marker of bone resorption. In the group that took acidic mineral water rich in calcium, no changes were observed.
A long-term 2-year randomized, double-blind, placebo-controlled trial showed the effectiveness of potassium citrate to increase bone mineral density (BMD) in the lumbar region. Participants were non-vegetarians aged 65-80 years, male and female. One group of participants received 60 millimoles of potassium citrate, and the second group received a placebo. As a result, the test group experienced an increase in BMD by 1.7 ± 1.5%. Also, these people had a lower risk score for fracture compared to the placebo group.
Alkaline therapy opposite studies
Opponents of the theory of an alkaline diet believe that bones can not be the main neutralizers of acid in the body. The opinion is based on a quantitative calculation of the depletion time of the supply of alkali in the bones of people with chronic metabolic acidosis. In this disease, the blood pH of patients often exceeds the lower limit of the norm of 7.35. Every day in their bodies, an additional 12-19 mmol of acid is formed, which must be buffered with the same amount of alkali. The bone consists of calcium hydroxyapatite and contains about 25,000 millimoles of alkali. If you spend 19 millimoles per day, this reserve will be used up in less than 4 years.
Observations supplement the arguments of the opponents of the theory of an alkaline diet that the production of sulfuric acid and organic acids decreases in renal failure.
The results of studies demonstrating a positive acid balance from alkali therapy are also subject to doubt. The authors of several articles point to errors in the methods of measuring the excretion of acid.
Opponents of alkali therapy for the treatment of osteoporosis refer to the results of a meta-analysis of cohort data and epidemiological studies.
One 2-year randomized placebo-controlled study involved 276 women aged 55-65 years. All participants were in the postmenopausal period. Scientists divided all participants into 4 groups. The first group received high doses of potassium citrate: 55.5 mEq per day. The second group is a low dose of potassium citrate: 18.5 mEq per day. The third group is a placebo. The fourth group received the natural equivalent of 18.5 mEq of lye in the form of 300g of additional fruits or vegetables per day. The results showed no persistent changes in bone renewal or mineral density in any group. Temporary improvements were observed only in the group receiving high doses of potassium citrate. After 4 to 6 weeks, a decrease in the level of deoxypyridinoline, a marker of bone resorption, was registered. However, after 3 months, the value returned to its original level.
Scientists have evaluated the effect of acid excretion on the balance of calcium in the urine when using alkaline supplements. This meta-analysis examined the dynamics of calcium balance due to changes in the amount or type of protein in food. There was a linear relationship between the increase in urinary excretion of both acid and calcium. Moreover, the calcium balance remained unchanged. No association was found between excessive acid excretion and changes in N-telopeptides, a marker of bone resorption. The researchers concluded that calcium balance is not a direct indicator of bone health.
Thus, in some large-scale studies, scientists have found no evidence of the effect of an acidic diet on bone density and fracture frequency.
Study of acid-base balance regulation
The arguments of supporters and opponents of the theory of the benefits of an alkaline diet are diametrically opposed.
Scientists at the University of California suggested that difference in opinion is caused by a lack of information about the regulation mechanisms of acid-base balance. In their view, the following issues remain unclear:
- What is the impact of acid on bones in healthy people?
- Does an acidic diet increase the acid balance in the bodies of healthy people?
- What other systems, besides bones, can buffer excessive acid load? Like muscles?
- In addition to sulfuric acid, what other acids are produced by the body at the systemic level and can affect bone density?
Scientists point out that an acidic diet can harm bones, but in quantitative terms, it will be significantly inferior to more serious factors. For example, physical inactivity, weight, gender, and age increase the risk of fractures more than coffee, tobacco, and a lack of trace elements.
In healthy people, increasing the acidity of the diet increases the pH of the blood. The concentration of hydrogen ions in the blood increases, while the level of bicarbonate in the blood plasma decreases. The study showed that with an acid load of more than 1 millimoles per kilogram of weight per day, homeostatic mechanisms could not maintain previous levels of hydrogen and bicarbonate ions.
Acid levels also increase with age. As shown in a meta-analysis of 971 healthy people, as the age increases from 20 to 80 years, the level of blood acidity decreases by 7%. During this time, the concentration of bicarbonate in the plasma reduces by about 12%.
Healthy people are also prone to a tendency for kidney function to deteriorate as they age. To study this mechanism, researchers observed patients with stage 2 chronic kidney disease (CKD-2). The degree of kidney failure in these people was similar to reduced kidney function in the elderly. The kidneys of patients with CKD-2 had a reduced ability to remove the acid. As a result, their body tissues accumulated more hydrogen ions than those of patients with CKD 1. These data demonstrate that high levels of acid contribute to the development of kidney failure. Treatment of patients with CKD 1, 2 with bicarbonate slowed the degradation of kidney function and delayed the onset of dialysis.
In the process of studying the mechanisms of regulation of the acid-base balance, a hypothesis was formulated that the production of organic acids regulates the systemic pH of the blood. A study of overweight people who starved or followed a ketone diet revealed this mechanism of regulation. In the first group, the subjects received ammonium chloride (acid). They had both reduced production of ketoacid and decreased excretion of acid in the urine. In the second group, people received sodium bicarbonate (lye). In their case, the situation was the opposite: increased acid production, acid excretion in the urine, and acid levels in the blood.
Thus, quantitative changes in the production of organic acids can be an essential mechanism for regulating systemic acid levels.
Conclusions
Scientists at the University of California suggest that all the accumulated research results are correct, but combine them into a single system.
The accumulated facts are as follows:
- Positive acid balance is regulated not only by the bone tissue
- Endogenous acid production increases and decreases to maintain the systemic pH of the blood
- More young people can maintain pH in the higher range of normal. Older people –
only at low levels of the norm
- As kidney function decreases, acid excretion decreases
- High acid levels lead to more rapid damage to the kidneys
- A diet high in acid precursors increases the acid load on the body
- Factors of age, gender, physical inactivity, and race are quantitatively more important for determining bone health than diet
Thus, scientists suggest that older adults with impaired kidney function can obtain the most significant benefit from an alkaline diet.
