Urine alkalization facilitates uric acid excretion

Abstract

Background: Increase in the incidence of hyperuricemia associated with gout as well as hypertension, renal diseases and cardiovascular diseases has been a public health concern. We examined the possibility of facilitated excretion of uric acid by change in urine pH by managing food materials.

Methods: Within the framework of the Japanese government's health promotion program, we made recipes which consist of protein-rich and less vegetable-fruit food materials for H+-load (acid diet) and others composed of less protein but vegetable-fruit rich food materials (alkali diet). Healthy female students were enrolled in this consecutive 5-day study for each test. From whole-day collected urine, total volume, pH, organic acid, creatinine, uric acid and all cations (Na+,K+,Ca(2+),Mg(2+),NH₄+) and anions (Cl⁻,SO₄(2-),PO₄⁻) necessary for the estimation of acid-base balance were measured.

Results: Urine pH reached a steady state 3 days after switching from ordinary daily diets to specified regimens. The amount of acid generated ([SO₄(2-)] +organic acid-gut alkai) were linearly related with those of the excretion of acid (titratable acidity+ [NH4+] - [HCO3⁻]), indicating that H+ in urine is generated by the metabolic degradation of food materials. Uric acid and excreted urine pH retained a linear relationship, where uric acid excretion increased from 302 mg/day at pH 5.9 to 413 mg/day at pH 6.5, despite the fact that the alkali diet contained a smaller purine load than the acid diet.

Conclusion: We conclude that alkalization of urine by eating nutritionally well-designed food is effective for removing uric acid from the body.

Figure 1

Effect of acid (square) and alkali (diamond) diets on urine pH. Data are presented as mean ± SD. Asterisks indicate statistical significance between two groups (p < 0.002).

Figure 2

Relationship between endogenous acid generation and renal acid excretion. Diamonds indicate data for the alkali diet and squares those for the acid diet. The equation for the straight line adopted to data by the least square method is y = 0.834 × + 27.09 (R² = 0.362, n = 102, p < 0.01). The lines above and below the regression line are the 99% confidence limits.

Figure 3

Relationship between excreted uric acid as expressed in mg uric acid in urine per day and urine pH. Diamonds indicate data for the alkali diet and squares those for the acid diet. Equation for the straight line obtained by the least square method is y = 165x-669(R² = 0.342, n = 102, p < 0.01). The lines above and below the regression line are the 99% confidence limits.