Daily Green Tea Infusions in Hypercalciuric Renal Stone Patients: No Evidence for Increased Stone Risk Factors or Oxalate-Dependent Stones

Oxalates: Dietary Oxalates and Kidney Inflammation: A Literature Review

This literature review explores the role of dietary oxalate in the development of chronic inflammatory kidney disease in middle-aged and older individuals. The authors pose the following questions: Is oxalate produced endogenously? If food sources contribute to chronic kidney disease and inflammation, what are those foods? What role do cultural food preparation and cooking play in denaturing food oxalates? The concentration of oxalates found within the body at any particular time is not limited to edible plants; normal human metabolic processes of breaking down ascorbic acid may create up to 30 mg of oxalate daily. Research supports urolithiasis as a common urologic disease in industrialized societies. Approximately 80% of kidney stones are composed of calcium oxalate, resulting in hyperoxaluria. Exogenous (originating outside the cell or organism) oxalate sources include ascorbic acid, amino acids, and glyoxal metabolism. Additional research estimates the daily endogenous (produced within the cell or organism) production of oxalate to be 10-25 mg. Suboptimal colonization of oxalate-degrading bacteria and malabsorptive disease are also contributing factors to the development of chronic kidney disease. Oxalate transcellular processes, though poorly understood, rely on multifunctional anion exchangers, and are currently being investigated. A review of research showed that normal human metabolic processes, including the breakdown of ascorbic acid, account for 35-55% of circulating oxalates and can create ≤30 mg of circulating serum oxalate daily. Glyoxylic acid accounts for 50-70% of circulating urinary oxalate in compromised individuals with liver glycation, bacterial insufficiencies, malabsorption, and anion exchange challenges. For persons with a family history of kidney stones, consumption of foods high in oxalates may be consumed in moderation, provided there is adequate calcium intake in the diet to decrease the absorption of oxalates from the meal ingested.

Unlocking New Approaches to Urolithiasis Management Via Nutraceuticals

Urolithiasis, commonly known as kidney stones, is characterized by the formation of hard deposits in the urinary tract. These stones can cause severe pain and discomfort, and their management typically involves a combination of medical interventions and lifestyle modifications. According to the literature, 30% and 50% of urolithiasis cases recur. Between 9 and 12% of persons in industrialised countries are predicted to have urolithiasis at some time. Due to the high frequency of stone formation, recurrent nature, and prevalence in adults, it has a significant impact on society, the person, and the health care system. Adopting the best prophylactic measures is crucial in light of these developments to decrease the impact of urolithiasis on individuals and society. In recent years, there has been growing interest in the potential role of nutraceuticals in the management of urolithiasis. Nutraceuticals, such as herbal extracts, vitamins, minerals, and probiotics, have gained recognition for their potential in promoting urinary health and reducing the risk of urolithiasis. These compounds can aid in various ways, including inhibiting crystal formation, enhancing urine pH balance, reducing urinary calcium excretion, and supporting kidney function. Additionally, nutraceuticals can help alleviate symptoms associated with urolithiasis, such as pain and inflammation. While medical interventions remain crucial, incorporating nutraceuticals into a comprehensive management plan can offer a holistic approach to urolithiasis, improving patient outcomes and quality of life. Therefore, nutraceuticals may be a desirable choice for treating and avoiding recurring urolithiasis for patients and medical professionals. Therefore, the present study has focused on nutraceuticals' role in preventing urolithiasis.

The Protective Role of Dietary Polyphenols in Urolithiasis: Insights into Antioxidant Effects and Mechanisms of Action

Urolithiasis is a common urological disease with increasing prevalence and high recurrence rates around the world. Numerous studies have indicated reactive oxygen species (ROS) and oxidative stress (OS) were crucial pathogenic factors in stone formation. Dietary polyphenols are a large group of natural antioxidant compounds widely distributed in plant-based foods and beverages. Their diverse health benefits have attracted growing scientific attention in recent decades. Many literatures have reported the effectiveness of dietary polyphenols against stone formation. The antiurolithiatic mechanisms of polyphenols have been explained by their antioxidant potential to scavenge free radicals and ROS, modulate the expression and the activity of endogenous antioxidant and prooxidant enzymes, regulate signaling pathways associated with OS, and maintain cell morphology and function. In this review, we first describe OS and its pathogenic effects in urolithiasis and summarize the classification and sources of dietary polyphenols. Then, we focus on the current evidence defining their antioxidant potential against stone formation and put forward challenges and future perspectives of dietary polyphenols. To conclude, dietary polyphenols offer potential applications in the treatment and prevention of urolithiasis.

Diet and Stone Disease in 2022

Diet plays a central role in the development and prevention of nephrolithiasis. Although pharmacologic treatment may be required for some patients who are resistant to dietary measures alone, dietary modification may be sufficient to modulate stone risk for many patients. While there is no single specialized diet for stone prevention, several dietary principles and recommendations for stone prevention are supported by practice guidelines, including adequate fluid intake, modest calcium intake, low dietary sodium, and limited animal protein. In this review, we summarized the evidence supporting these dietary recommendations and reviewed the current literature regarding specific dietary components and comprehensive diets for stone prevention.

Tea Infusions as a Source of Phenolic Compounds in the Human Diet

Phenolic compounds are components with proven beneficial effects on the human body, primarily due to their antioxidant activity. In view of the high consumption of tea and the numerous factors that affect the nutritional value of its infusions, the aim of this study was to identify the effects of tea type and duration of leaf extraction with water on the levels of phenolic compounds and other components that determine biological activity (oxalates, Ca, Na, Cu, and Mn). Based on assays, infusions of red tea prepared for 20 min were found to be the best source of phenolics (202.9 mg/100 mL), whereas the lowest level of these compounds was determined in infusions of black tea extracted from leaves for 30 min (46.9 mg/100 mL). The highest degree of increase in polyphenol content (by approx. 50%) was noted in red and green tea infused for between 10 and 20 min, whereas for black tea, polyphenol levels decreased with time. The biological activity of tea infusions appears to be determined to the greatest extent by the interactions between phenolic compounds and oxalates (r = 0.6209), calcium (r = 0.8516), and sodium (0.8045). A daily intake of three to four mugs (1 L) of tea infusions provides the human body the entire amount of phenolics recommended for health reasons (as regards red tea, this is possible at 1/3 of the volume) and covers the daily requirement for manganese, as well as (partially) copper.

Modulation of Rat Kidney Stone Crystallization and the Relative Oxidative Stress Pathway by Green Tea Polyphenol

The role of tea polyphenol (TP) in modulating kidney stone crystallization and regulating the relative nephropathy pathway of rats was investigated. Calcium oxalate (CaOx) crystallization and oxidative stress are essential for kidney stone diseases. The kidney stone model in a rat was established by using ethylene glycol to affect the oxalic acid metabolism. The crystallization process of CaOx in the rat kidney was modulated by different TP intakes. At the same time, the effects of different types of CaOx, extracted from the rat kidney, on the proliferation and differentiation of HK-2 cells were also studied. The results showed that calcium oxalate monohydrate crystals were obtained in the blank control and the low-dose TP groups. However, CaOx crystals extracted from higher-TP-intake groups were mainly calcium oxalate dihydrate. Moreover, the size of the CaOx crystals produced in TP intake groups was much smaller than that of the blank control group. Cell experiment results show that TP can effectively reduce the damage of CaOx crystals to HK-2 cells. Further research found that TP can significantly improve oxidative stress in cases of kidney stones. TP has been proven to control CaOx crystallization in vitro, but the in vivo research results obtained through the rat stone model in this paper are novel and originally important for researching the relationship between tea drinking and preventive treatment of kidney stone diseases.

Tea and coffee consumption and the risk of urinary stones-a systematic review of the epidemiological data

OBJECTIVE

To explore the relationship between the consumption of coffee and tea with urolithiasis. We evaluated large epidemiological and small clinical studies to draw conclusions regarding their lithogenic risk.

METHODS

A systematic review was performed using the Medline and Scopus databases, in concordance with the PRISMA statement. English, French, and Spanish language studies regarding the consumption of caffeinated and decaffeinated coffee and tea, and the relationship to urinary stone disease were reviewed. Case reports and letters, unpublished studies, posters, and comments were excluded.

RESULTS

As per the inclusion criteria, 13 studies were included in the final review. Most studies, including four large prospective studies and one meta-analysis, reported a reduced risk of stone formation for coffee and tea. Caffeine has a diuretic effect and increases the urinary excretion of calcium, but if these losses are compensated for, moderate caffeine intakes may have little or no deleterious effects. Green and Herbal teas infused for short time had low oxalate content compared to black tea.

CONCLUSION

There is no evidence that moderate consumption of coffee raises the risk for stone formation in healthy individuals, provided the recommended daily fluid intake is maintained. The currently available literature supports in general a protective role for tea against the stone formation, mainly for green tea. However, heterogeneity of published data and lack of standardization needs to be addressed before final and clear conclusions can be given to patients and to the public in general.

Tea and coffee consumption and pathophysiology related to kidney stone formation: a systematic review

OBJECTIVE

To explore the mechanisms behind the potential protective effect of coffee and tea consumption, regarding urinary stone formation, previously demonstrated in large epidemiological studies.

METHODS

A systematic review was performed using the Medline, Cochrane library (CENTRAL) and Scopus databases, in concordance with the PRISMA statement. English, French and Spanish language studies, regarding the consumption of caffeinated and decaffeinated coffee and tea, and the relationship to urinary stone formation were reviewed. Meta-analyses, systematic reviews, case reports and letters, unpublished studies, posters and comments abstracts were excluded.

RESULTS

As per the inclusion criteria, 13 studies were included in the final review. The major findings show that caffeine increases urinary excretion of calcium, sodium and magnesium, in addition to a diuretic action with consumption > 300-360 mg (approximately four cups of coffee). Together with other components of coffee, this beverage might have potential protective effects against the formation of urinary stones. Tea exerts many protective effects against stone formation, through the accompanying water intake, the action of caffeine and the effects of components with antioxidant properties.

CONCLUSION

Caffeine has a hypercalciuric effect, balanced partially by a diuretic effect which appears after consumption of large quantities of caffeine. The current available literature supports in general, a potentially protective role for tea against stone formation, mainly for green tea. Additional standardization in this field of research, through specification of tea and coffee types studied, and their respective compositions, is needed for further clarification of the relation between coffee, tea and urinary stones.

Preprotection of Tea Polysaccharides with Different Molecular Weights Can Reduce the Adhesion between Renal Epithelial Cells and Nano-Calcium Oxalate Crystals

Crystal adhesion is an important link in the formation of kidney stones. This study investigated and compared the adhesion differences between nano-calcium oxalate monohydrate (COM) and human renal proximal tubule epithelial (HK-2) cells before and after treatment with tea polysaccharides (TPSs) TPS0, TPS1, TPS2, and TPS3 with molecular weights of 10.88, 8.16, 4.82, and 2.31 kDa, respectively. TPS treatment effectively reduced the damage of COM to HK-2 cells, thereby resulting in increased cell activity, decreased release of lactate dehydrogenase, cell morphology recovery, decreased level of reactive oxygen species, increased mitochondrial membrane potential, increased lysosomal integrity, decreased expression of adhesion molecule osteopontin and eversion of phosphatidylserine, and decreased crystal adhesion. Among the TPSs, TPS2 with moderate molecular weight had the best protective effect on cells and the strongest effect on the inhibition of crystal adhesion. Thus, TPS2 may be a potential anticalculus drug.

Comparison of the adhesion of calcium oxalate monohydrate to HK-2 cells before and after repair using tea polysaccharides

Background: Kidney stone formation is closely related to renal epithelial cell damage and the adhesion of calcium oxalate crystals to cells. Methods: In this research, the adhesion of human kidney proximal tubular epithelial cells (HK-2) to calcium oxalate monohydrate crystals with a size of approximately 100 nm was studied. In addition, the inhibition of crystal adhesion by four tea polysaccharides (TPS0, TPS1, TPS2, and TPS3) with the molecular weights of 10.88, 8.16, 4.82, and 2.31 kDa, respectively were compared. Results: When oxalic acid-damaged HK-2 cells were repaired, cell viability increased. By contrast, reactive oxygen species level, phosphatidylserine eversion, and osteopontin expression decreased, thus indicating that tea polysaccharides have a repairing effect on damaged HK-2 cells. Moreover, after repairing the damaged cells, the amount of adherent crystals was reduced. The repair effect of tea polysaccharides is closely related to molecular weight, and TPS2 with the moderate molecular weight displayed the best repair effect. Conclusion: These results suggest that tea polysaccharides, especially TPS2, may inhibit the formation and recurrence of calcium oxalate kidney stones.

A Study of Diet and Lifestyle and the Risk of Urolithiasis in 1,519 Patients in Southern China

Background

This study aimed to evaluate the risk factors associated with the development of urolithiasis in a population in Southern China.

Material/Methods

A questionnaire-based study was conducted between March 2017 to April 2018 that included 1,519 patients in Southern China and included questions on patient demographics, diet, and lifestyle. Patients were divided into the urolithiasis group who had urinary calculi and the control group.

Results

There were 829 patients (54.6%) in the urolithiasis group and 690 patients (45.4%) in the control group. Using a chi-squared (χ²) test, 13 variables were found to be significantly associated with urolithiasis, including age, physical activity, and dietary factors that included high sodium, protein, fat, lean meat, vegetables, pickled food, fluid intake, drinking habits and tea consumption, and frequency and duration of physical exercise. Multivariate logistic regression analysis showed that dietary factors, including vegetables (OR, 0.856; 95% CI, 0.769–0.948), pickled foods (OR, 1.271; 95% CI, 1.030–1.357), and animal protein intake (OR, 1.138; 95% CI, 1.031–1.258), drinking strong tea (OR, 0.793; 95% CI, 0.702–0.897), fluid intake (OR, 0.758; 95% CI, 0.644–0.816), and duration of physical exercise (OR, 0.840; 95% CI, 0.808–0.973) were significantly associated with the occurrence of urolithiasis and were independent risk factors.

Conclusions

High consumptions of pickled foods and animal protein were the main risk factors for the development of urolithiasis in a population of southern China, but high fluid intake with a preference for strong tea, a diet of vegetables, and physical exercise were protective factors.