High-calcium intake abolishes hyperoxaluria and reduces urinary crystallization during a 20-fold normal oxalate load in humans

Association between milk consumption and kidney stones in U.S. adults: results from NHANES 2007-2018

Background

Dietary strategies play a crucial role in the prevention of kidney stones. While milk is known for its rich nutritional content, its impact on kidney stone formation remains unclear. This study aimed to examine the relationship between milk consumption and the risk of kidney stones among U.S. adults.

Methods

We included 24,620 participants aged 20 and older from the National Health and Nutrition Examination Survey (2007-2018). Milk consumption was defined based on each participant's response to the questionnaire item on "Past 30 day milk product consumption." Kidney stones history was self-reported by participants. The analysis employed weighted multivariate logistic regression models, followed by subgroup analyses for result validation, and explored the age-related dynamics of milk consumption's effect on kidney stone risk using a restricted cubic spline model.

Results

Adjusted findings revealed that higher milk intake was associated with a decreased risk of kidney stones (odds ratio [OR] = 0.90, 95% confidence interval [CI] 0.85-0.96), notably among women (OR = 0.86, 95% CI 0.80-0.92) but not significantly in men (OR = 0.94, 95% CI 0.86-1.02). Smoothed curves across all ages showed that women consuming milk had a lower incidence of kidney stones than those who did not, particularly with regular consumption.

Conclusion

This study uncovered that across all age groups, higher frequency of milk consumption in women is associated with a reduced risk of kidney stones. However, further prospective cohort studies are needed to confirm this finding.

Pharmacologic treatment of kidney stones: Current medication and pH monitoring

Nephrolithiasis is a globally prevalent urologic condition associated with significant morbidity and patient discomfort. Current management of kidney stones includes both surgical and pharmacologic interventions. Though surgery may be necessary under certain circumstances, pharmacologic treatment is a more affordable, readily available, and a less invasive option for patients. A comprehensive scoping review was conducted to summarize the available literature on the pharmacologic strategies for managing the predominant stone types including calcium oxalate, calcium phosphate, uric acid, struvite, and cystine stones. Central to these therapeutic approaches is the regulation of factors such as urine pH, stone crystallization, and patient metabolics that precipitate stone development and growth. This review highlights the pharmacological options available for treating each kidney stone type, emphasizing the importance of patient tailored medical management that should be considered by every physician.

2022 Recommendations of the AFU Lithiasis Committee: Medical management - from diagnosis to treatment

The morphological-compositional analysis of urinary stones allows distinguishing schematically several situations: dietary, digestive, metabolic/hormonal, infectious and genetic problems. Blood and urine testing are recommended in the first instance to identify risk factors of urinary stone disease in order to avoid recurrence or progression. The other objective is to detect a potential underlying pathology associated with high risk of urinary stone disease (e.g. primary hyperparathyroidism, primary or enteric hyperoxaluria, cystinuria, distal renal tubular acidosis) that may require specific management. Lifestyle-diet measures are the basis of the management of all stone types, but pharmacological treatments may be required. METHODOLOGY: These recommendations were developed using two methods: the Clinical Practice Recommendation (CPR) method and the ADAPTE method, depending on whether the question was considered in the European Association of Urology (EAU) recommendations (https://uroweb.org/guidelines/urolithiasis) [EAU 2022] and their adaptability to the French context.

The Association between Dietary Sugar Intake and Nephrolithiasis: Results from National Health and Nutrition Examination Survey 2007-2018

BACKGROUND

Dietary sugar intake is gradually considered a risk factor for many diseases. A sugary diet was positively associated with risk of nephrolithiasis, but the specific relationships remain undefined.

OBJECTIVES

To determine associations between risk of nephrolithiasis and dietary sugar intake.

METHODS

This cross-sectional study involved 21,590 participants based on the National Health and Nutrition Examination Survey from 2007 to 2018. Amounts of dietary sugar intake (g/d) were the main exposure, including total sugar intake, added sugar intake, and food sources. Associations were analyzed by logistic regression models and restricted cubic splines using complex weighted designs.

RESULTS

Weighted mean intake [standard error] of total sugar and added sugar were 111.2 [2.0] g/d and 73.7 [1.9] g/d in participants with nephrolithiasis, respectively. In the fully adjusted regression model, compared to those in quartile 1, the population in quartile 4 of total sugar intake showed a significant risk of nephrolithiasis [odds ratio (OR): 1.23; 95% confidence interval (CI): 1.00-1.51]; OR for added sugar intake was 1.56 (95% CI: 1.25-1.94). The risks of nephrolithiasis increased steadily when total sugar and added sugar intake exceeded ∼150 g/d and 63 g/d in restricted cubic spline analyses, respectively. The highest sugar intake from beverages was associated with an increased risk of nephrolithiasis (OR for total sugar: 1.36; 95% CI: 1.07-1.72; OR for added sugar: 1.37; 95% CI: 1.09-1.73). Added sugar intake from meat, egg, and oil was significantly associated with risk of nephrolithiasis (quartile 4, OR: 1.22; 95% CI: 1.02-1.47), whereas total sugar intake from dairy products was in reverse (quartile 4, OR: 0.67; 95% CI: 0.54-0.82).

CONCLUSIONS

Total and added sugar intake, sugar intake from beverages, and added sugar intake from meat, egg, and oil were associated with an increased risk of nephrolithiasis, whereas total sugar intake from dairy products was negatively associated.

The effect of nutritional factors on urolithiasis: A case-control study

Urolithiasis, a prevalent chronic kidney disease affecting all age groups, can be influenced by nutritional factors. The incidence of urolithiasis in Asian countries ranges from 1% to 19.1%, attributed to geographical and lifestyle differences. In Iran, several risk factors, including ethnicity, dietary habits, gender, and age, are associated with urolithiasis. This study aimed to assess the impact of nutritional factors on kidney and urinary tract stone formation. This case-control study enrolled 127 newly diagnosed urolithiasis patients, and 127 matched healthy participants between February to May 2017. Exclusion criteria included diabetes and acute or chronic renal failure. Data were collected using the Food Frequency Questionnaire (FFQ) and analyzed using chi-square and logistic regression tests. Water (95% CI: 0.09-0.89, OR=0.28), natural juices (95% CI: 0.10-0.65, OR=0.53), mineral water (95% CI: 0.05-0.64, OR=0.18), legumes (95% CI: 0.00-0.38, OR=0.032), butter, cream, or peppermint (95% CI: 0.09-0.95, OR=0.30), and ice cream (95% CI: 0.07-0.54, OR=0.203) had a significant protective effect against kidney and urinary tract stone formation. Conversely, tea consumption (95% CI: 1.15-7.99, OR=4.70), beverages (95% CI: 4.45-23.32, OR=23.32), coffee (95% CI: 1.63-11.78, OR=4.39), bread (95% CI: 1.1-10.59, OR=3.37), meat (95% CI: 1.01-8.01, OR=2.85), liver (95% CI: 3.37-488.90, OR=40.58), fish (95% CI: 2.89-216.39, OR=25.03), and various canned foods (95% CI: 1.34-10.25, OR=3.70) were significantly associated with kidney and urinary tract stone risk. These findings showed that the risk of urinary stones formation had a significant relationship with dietary habits. Therefore, the correct dietary pattern and sufficient fluid consumption may play an important role in preventing urinary stones.

The effectiveness of citrates and pyridoxine in the treatment of kidney stones

The prevalence of nephrolithiasis is increasing across all demographic groups. Apart from the morbidity associated with an acute occurrence, preventative treatment is essential for stone disease, which can become a long-term problem. Simple interventions like fluid intake optimization and dietary modification are effective for most stone types. However, patients with specific metabolic abnormalities may require pharmaceutical therapy if lifestyle changes are insufficient to reduce the risk of stone recurrence. The treatment of citrates and/or pyridoxines may help eliminate or prevent recurrences of kidney stones, especially when they are composed of uric acid, calcium oxalate, calcium phosphate, or the latter two together. In cases of struvite stones, which often necessitate a surgical approach, acetohydroxamic acid emerges as a valuable second-line treatment option. Thiol-binding agents may be needed for cystinuria, as well as lifestyle modifications. Successful treatment reduces stone recurrence and the need to remove stones surgically.

Mineral content variations between Australian tap and bottled water in the context of urolithiasis

Objectives

The objective of this study is to investigate the variations in mineral content of tap drinking water across major Australian cities, compared with bottled still and sparkling water, and discuss the possible implications on kidney stone disease (KSD).

Materials and Methods

The mineral composition of public tap water from 10 metropolitan and regional Australian cities was compared using the drinking water quality reports published from 2019 to 2021 by the respective water service utilities providers. Specifically, average levels of calcium, bicarbonate, magnesium, sodium, potassium, and sulphates were compared with published mineral content data from bottled still and sparkling drinking water in Australia.

Results

The median or mean (depending on report output) mineral composition was highly variable for calcium (range 1.3 to 20.33 mg/L), magnesium (range 1.1 to 11.2 mg/L), bicarbonate (range 12 to 79 mg/L), sodium (range 3 to 47.1 mg/L), potassium (range 0.4 to 3.23 mg/L) and (sulphates range <1 to 37.4 mg/L). Calcium, magnesium and bicarbonate levels in tap water were lower than in bottled sparkling water. Consumption of 3 L/day of the most calcium rich tap water would fulfil 4.7% of the RDI, compared with 8.7% with bottled sparkling water. Consumption of 3 L of the most magnesium rich tap water would fulfil 8% of the RDI, compared with 13.6% with bottled sparkling water.

Conclusion

The mineral content of tap drinking water varied substantially across major Australian city centres. Bottled sparkling water on average provided higher levels of calcium, bicarbonate and magnesium and may be preferred for prevention of calcium oxalate stones. These findings may assist counselling of patients with KSD depending on geographic location in the context of other modifiable risk factors and 24‐h urine analysis results.

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.

The health effects of soy: A reference guide for health professionals

Soy is a hotly debated and widely discussed topic in the field of nutrition. However, health practitioners may be ill-equipped to counsel clients and patients about the use of soyfoods because of the enormous, and often contradictory, amount of research that has been published over the past 30 years. As interest in plant-based diets increases, there will be increased pressure for practitioners to gain a working knowledge of this area. The purpose of this review is to provide concise literature summaries (400-500 words) along with a short perspective on the current state of knowledge of a wide range of topics related to soy, from the cholesterol-lowering effects of soy protein to the impact of isoflavones on breast cancer risk. In addition to the literature summaries, general background information on soyfoods, soy protein, and isoflavones is provided. This analysis can serve as a tool for health professionals to be used when discussing soyfoods with their clients and patients.

Trimethylamine N-oxide promotes hyperoxaluria-induced calcium oxalate deposition and kidney injury by activating autophagy

Calcium oxalate (CaOx) is the most common component of kidney stones. Oxidative stress, inflammation and autophagy-induced cell death are the major causes of CaOx crystal deposition and CaOx crystal deposition can further lead to kidney injury. Trimethylamine N-oxide (TMAO), a gut microbiota-derived metabolite, plays an important role in the pathogenesis of many diseases, such as atherosclerosis, diabetes and chronic kidney disease, but the effect of TMAO on hyperoxaluria-induced CaOx crystal deposition and kidney injury remains unknown. We hypothesize that TMAO aggravates CaOx crystal deposition via promoting CaOx-mediated cell death. C57Bl/6 mice were given high-oxalate diet as a model of hyperoxaluria. TMAO was provided via drinking water. Serum TMAO levels increased 15 days after CaOx treatment (6.30 ± 0.17 μmol/L vs. 34.65 ± 8.95 μmol/L). High-oxalate diet induced inflammation, CaOx deposition and kidney injury, which TMAO aggravated. In accordance, TMAO intensified high-oxalate diet induced oxidative stress, autophagy and apoptosis. Moreover, TMAO enhanced CaOx crystal adhesion to HK-2 cells and reduced cell viability (from 88.9 ± 1.6% to 75.0 ± 2.7%). Protein kinase R-like endoplasmic reticulum kinase (PERK) may mediate these TMAO effects, as TMAO promoted PERK phosphorylation. Consistently, PERK knockdown alleviated TMAO-evoked CaOx-autophagy, apoptosis and oxidative stress in HK-2 cells. In conclusion, TMAO can aggravate hyperoxaluria-induced kidney injury by triggering the PERK/ROS pathway, which enhances autophagy, apoptosis and inflammation, and facilitates CaOx crystal deposition in renal tubular cells.

Acute Oxalate Nephropathy Caused by Excessive Vegetable Juicing and Concomitant Volume Depletion

Acute oxalate nephropathy (AON) induced by high dietary intake of oxalate-rich food is a rare cause of acute kidney injury and end-stage renal disease (ESRD). We describe a 68-year-old man with adequate baseline renal function who developed severe AON and ESRD. Six months earlier, he started a daily oxalate-rich fruit and vegetable juice diet high in spinach, with a calculated daily oxalate dietary intake of 1500 mg, about 10 times a typical diet. Renal biopsy showed extensive tubular oxalate deposits and acute tubular damage; the renal tissue was relatively free of chronic changes such as glomerulosclerosis, tubular atrophy, and interstitial fibrosis. A year later, he remains dialysis dependent.

Calcium and Vitamin D Supplementation and Their Association with Kidney Stone Disease: A Narrative Review

Kidney stone disease is a multifactorial condition influenced by both genetic predisposition and environmental factors such as lifestyle and dietary habits. Although different monogenic polymorphisms have been proposed as playing a causal role for calcium nephrolithiasis, the prevalence of these mutations in the general population and their complete pathogenetic pathway is yet to be determined. General dietary advice for kidney stone formers includes elevated fluid intake, dietary restriction of sodium and animal proteins, avoidance of a low calcium diet, maintenance of a normal body mass index, and elevated intake of vegetables and fibers. Thus, balanced calcium consumption protects against the risk for kidney stones by reducing intestinal oxalate availability and its urinary excretion. However, calcium supplementation given between meals might increase urinary calcium excretion without the beneficial effect on oxalate. In kidney stone formers, circulating active vitamin D has been found to be increased, whereas higher plasma 25-hydroxycholecalciferol seems to be present only in hypercalciuric patients. The association between nutritional vitamin D supplements and the risk for stone formation is currently not completely understood. However, taken together, available evidence might suggest that vitamin D administration worsens the risk for stone formation in patients predisposed to hypercalciuria. In this review, we analyzed and discussed available literature on the effect of calcium and vitamin D supplementation on the risk for kidney stone formation.

Urine and stone analysis for the investigation of the renal stone former: a consensus conference

The Consensus Group deliberated on a number of questions concerning urine and stone analysis over a period of months, and then met to develop consensus. The Group concluded that analyses of urine and stones should be routine in the diagnosis and treatment of urinary stone diseases. At present, the 24-h urine is the most useful type of urine collection, and accepted methods for analysis are described. Patient education is also important for obtaining a proper urine sample. Graphical methods for reporting urine analysis results can be helpful both for the physician and for educating the patient as to proper dietary changes that could be beneficial. Proper analysis of stones is also essential for diagnosis and management of patients. The Consensus Group also agreed that research has shown that evaluation of urinary crystals could be very valuable, but the Group also recognizes that existing methods for assessment of crystalluria do not allow this to be part of stone treatment in many places.

Simple dietary advice targeting five urinary parameters reduces urinary supersaturation in idiopathic calcium oxalate stone formers

Among 208 kidney stone patients referred within 2 years, 75 patients (66 men, nine women) with truly idiopathic calcium oxalate stones (ICSF) were recruited. Dietary advice (DA) aimed at (1) urine dilution, (2) reduced crystallization promotion (lowering oxalate), and (3) increased crystallization inhibition (increasing citrate). We recommended higher intakes of fluid and calcium with meals/snacks (reducing intestinal oxalate absorption) as well as increased alkali and reduced meat protein (acid) for increasing urinary citrate. The intended effects of DA were elevations in urine volume, calcium (U-Ca) and citrate (U-Cit) as well as reductions in oxalate (U-Ox) and uric acid (U-UA). We retrospectively calculated an adherence score (AS), awarding + 1 point for parameters altered in the intended direction and − 1 point for opposite changes. Calcium oxalate supersaturation (CaOx-SS) was calculated using Tiselius’ AP(CaOx) index EQ. DA induced changes (all p < 0.0001) in urine volume (2057 ± 79 vs. 2573 ± 71 ml/day) and U-Ca (5.49 ± 0.24 vs. 7.98 ± 0.38 mmol/day) as well as in U-Ox (0.34 ± 0.01 vs. 0.26 ± 0.01 mmol/day) and U-UA (3.48 ± 0.12 vs. 3.13 ± 0.10 mmol/day). U-Cit only tendentially increased (3.07 ± 0.17 vs. 3.36 ± 0.23 mmol/day, p = 0.06). DA induced a 21.5% drop in AP(CaOx) index, from 0.93 ± 0.05 to 0.73 ± 0.05 (p = 0.0005). Decreases in CaOx-SS correlated with AS (R = 0.448, p < 0.0005), and highest AS (+ 5) always indicated lowering of CaOx-SS. Thus, simple DA can reduce CaOx-SS which may be monitored by AS.

Enteric hyperoxaluria: role of microbiota and antibiotics

PURPOSE OF REVIEW

Enteric hyperoxaluria is commonly observed in malabsorptive conditions including Roux en Y gastric bypass (RYGB) and inflammatory bowel diseases (IBD). Its incidence is increasing secondary to an increased prevalence of both disorders. In this review, we summarize the evidence linking the gut microbiota to the risk of enteric hyperoxaluria.

RECENT FINDINGS

In enteric hyperoxaluria, fat malabsorption leads to increased binding of calcium to free fatty acids resulting in more soluble oxalate in the intestinal lumen. Bile acids and free fatty acids in the lumen also cause increased gut permeability allowing more passive absorption of oxalate. In recent years, there is more interest in the role of the gut microbiota in modulating urinary oxalate excretion in enteric hyperoxaluria, stemming from our knowledge that microbiota in the intestines can degrade oxalate. Oxalobacter formigenes reduced urinary oxalate in animal models of RYGB. The contribution of other oxalate-degrading organisms and the microbiota community to the pathophysiology of enteric hyperoxaluria are also currently under investigation.

SUMMARY

Gut microbiota might play a role in modulating the risk of enteric hyperoxaluria through oxalate degradation and bile acid metabolism. O. formigenes is a promising therapeutic target in this population; however, further studies in humans are needed to test its effectiveness.

Risk of Kidney Stones: Influence of Dietary Factors, Dietary Patterns, and Vegetarian-Vegan Diets

Nephrolithiasis is a common medical condition influenced by multiple environmental factors, including diet. Since nutritional habits play a relevant role in the genesis and recurrence of kidney stones disease, dietary manipulation has become a fundamental tool for the medical management of nephrolithiasis. Dietary advice aims to reduce the majority of lithogenic risk factors, reducing the supersaturation of urine, mainly for calcium oxalate, calcium phosphate, and uric acid. For this purpose, current guidelines recommend increasing fluid intake, maintaining a balanced calcium intake, reducing dietary intake of sodium and animal proteins, and increasing intake of fruits and fibers. In this review, we analyzed the effects of each dietary factor on nephrolithiasis incidence and recurrence rate. Available scientific evidence agrees on the harmful effects of high meat/animal protein intake and low calcium diets, whereas high content of fruits and vegetables associated with a balanced intake of low-fat dairy products carries the lowest risk for incident kidney stones. Furthermore, a balanced vegetarian diet with dairy products seems to be the most protective diet for kidney stone patients. Since no study prospectively examined the effects of vegan diets on nephrolithiasis risk factors, more scientific work should be made to define the best diet for different kidney stone phenotypes.

Medical therapy for nephrolithiasis: State of the art

The prevalence of nephrolithiasis is increasing worldwide. Understanding and implementing medical therapies for kidney stone prevention are critical to prevent recurrences and decrease the economic burden of this condition. Dietary and pharmacologic therapies require understanding on the part of the patient and the prescribing practitioner in order to promote compliance. Insights into occupational exposures and antibiotic use may help uncover individual risk factors. Follow-up is essential to assess response to treatment and to modify treatment plans to maximize therapeutic benefit.

Renal stones

Renal stone disease is a worldwide problem which carries significant morbidity. It frequently requires specialist urology intervention. Patients with recurrent disease and those at high risk require specialist investigations and review. Certain cases benefit from medical and surgical intervention. In this review, we discuss the pathophysiology, risk assessment, specialist investigations and various interventions, their rationale and evidence base. This review aims to provide an update of the previous publication in 2001 in this journal on this topic.

Adherence to the Mediterranean Dietary Pattern and Incidence of Nephrolithiasis in the Seguimiento Universidad de Navarra Follow-up (SUN) Cohort

BACKGROUND

Diet plays an important role in the pathogenesis of nephrolithiasis. Limited data are available to investigate the association between a Mediterranean dietary pattern and risk for nephrolithiasis.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

16,094 men and women without a history of nephrolithiasis who participated in the Seguimiento Universidad de Navarra Follow-up (SUN) Project.

PREDICTORS

A validated 136-item food frequency questionnaire was used to assess baseline adherence to a Mediterranean dietary pattern that is high in fruits, vegetables, nuts, fish, and legumes, but moderate in alcohol and low in meats, saturated fats, and sugars. A Mediterranean dietary pattern score was calculated and categorized into 3 groups (0-3, 4-6, and 7-9 points). Additional factors included in statistical models were sex, age, body mass index, smoking, physical activity, time spent watching television, following a medical nutritional therapy, water and energy intake, calcium and vitamin D supplementation, and history of hypertension or diabetes.

OUTCOMES

Incidence of nephrolithiasis. Participants were classified as having incident nephrolithiasis if they reported a physician-made diagnosis of nephrolithiasis during follow-up.

RESULTS

After a mean follow-up of 9.6 years, 735 new cases of nephrolithiasis were identified. The multivariable HRs of nephrolithiasis for the 2 highest categories of adherence to the Mediterranean dietary pattern, using the lowest category as the reference, were 0.93 (95% CI, 0.79-1.09) and 0.64 (95% CI, 0.48-0.87); P for trend=0.01. The risk for nephrolithiasis was lower with greater consumption of dairy products and vegetables and greater with higher monounsaturated fatty acid to saturated fatty acid ratio.

LIMITATIONS

No information for kidney stone composition.

CONCLUSIONS

Greater adherence to a Mediterranean dietary pattern was associated with reduced risk for incident nephrolithiasis. Additional longitudinal studies are needed.

Role of gut microbiota against calcium oxalate

Nephrolithiasis is a condition marked by the presence or formation of stones in kidneys. Several factors contribute to kidney stones development such as environmental conditions, type of dietary intake, gender and gastrointestinal flora. Most of the kidney stones are composed of calcium phosphate and calcium oxalate, which enter in to the body through diet. Both sources of oxalates become dangerous when normal flora of gastrointestinal tract is disturbed. Oxalobacter and Lactobacillus species exist symbiotically in the human gut and prevent stone formation by altering some biochemical pathways through production of specific enzymes which help in the degradation of oxalate salts. Both Oxalobacter and Lactobacillus have potential probiotic characteristics for the prevention of kidney stone formation and this avenue should be further explored.

Renal stone clinic survey: calcium stone formers' self-declared understanding of and adherence to physician's recommendations

Nothing is known about how well stone formers understand physician's explanations of stone formation, and a few data are available on adherence to provided recommendations. In this study, two groups of recurrent calcium stone formers (RCSFs) were compared. Group 1: 153 consecutive RCSF (118 men, 35 women) referred 1/2011-6/2014. At least 3 months after a 60-75 min consultation explaining metabolic evaluation and therapeutic measures, RCSF received a questionnaire by mail, regarding understanding of stone formation and adherence to therapeutic recommendations (diet, lifestyle, drug treatment). Response rate was 62 %. Group 2 (control): 81 consecutive RCSFs referred 7/2014-3/2016 (60 men, 21 women) were asked to answer the same questionnaire in the stone center while waiting for their follow-up consultation 3 months after starting prevention; response rate was 100 %. Alkali citrate was prescribed in 45 %. Answer sheets were analyzed anonymously, and frequencies of answers were compared by Chi-square test.

RESULTS

67 % (group 1) and 62 % (group 2) indicated >80 % understanding of the given information (NS). Over 80 % adherence to recommendations occurred in 26 and 30 % (NS). Most frequent changes in dietary/lifestyle habits were increases in calcium (93 vs. 89 %) and fluid intakes (81 vs. 78 %); lowering psychosocial stress (23 vs. 24 %) was least popular. Adherence to 100 % on 6-7 days/week was significantly more frequent for medication than for dietary/lifestyle interventions, both in group 1 (84 vs. 24 %, p < 0.001) and group 2 (91 vs. 28 %, p < 0.001).

CONCLUSIONS

(1) results do not differ whether RCSFs are voluntarily participating by mail or asked to answer questionnaires in the stone clinic; (2) pathophysiologic explanations of stone disease are understood to >80 % by 2/3 of RCSFs; (3) after 3 months, perfect adherence to recommended treatment is more frequent on alkali citrate than on dietary/lifestyle measures; and (4) increasing calcium and fluid intake are the most popular dietary measures.

Oxalate, inflammasome, and progression of kidney disease

PURPOSE OF REVIEW

Oxalate is an end product of metabolism excreted via the kidney. Excess urinary oxalate, whether from primary or enteric hyperoxaluria, can lead to oxalate deposition in the kidney. Oxalate crystals are associated with renal inflammation, fibrosis, and progressive renal failure. It has long been known that as the glomerular filtration rate becomes reduced in chronic kidney disease (CKD), there is striking elevation of plasma oxalate. Taken together, these findings raise the possibility that elevation of plasma oxalate in CKD may promote renal inflammation and more rapid progression of CKD independent of primary cause.

RECENT FINDINGS

The inflammasome has recently been identified to play a critical role in oxalate-induced renal inflammation. Oxalate crystals have been shown to activate the NOD-like receptor family, pyrin domain containing 3 inflammasome (also known as NALP3, NLRP3, or cryopyrin), resulting in release of IL-1β and macrophage infiltration. Deletion of inflammasome proteins in mice protects from oxalate-induced renal inflammation and progressive renal failure.

SUMMARY

The findings reviewed in this article expand our understanding of the relevance of elevated plasma oxalate levels leading to inflammasome activation. We propose that inhibiting oxalate-induced inflammasome activation, or lowering plasma oxalate, may prevent or mitigate progressive renal damage in CKD, and warrants clinical trials.

Loss of Cystic Fibrosis Transmembrane Regulator Impairs Intestinal Oxalate Secretion

Patients with cystic fibrosis have an increased incidence of hyperoxaluria and calcium oxalate nephrolithiasis. Net intestinal absorption of dietary oxalate results from passive paracellular oxalate absorption as modified by oxalate back secretion mediated by the SLC26A6 oxalate transporter. We used mice deficient in the cystic fibrosis transmembrane conductance regulator gene (Cftr) to test the hypothesis that SLC26A6-mediated oxalate secretion is defective in cystic fibrosis. We mounted isolated intestinal tissue from C57BL/6 (wild-type) and Cftr^-/- mice in Ussing chambers and measured transcellular secretion of [¹⁴C]oxalate. Intestinal tissue isolated from Cftr^-/- mice exhibited significantly less transcellular oxalate secretion than intestinal tissue of wild-type mice. However, glucose absorption, another representative intestinal transport process, did not differ in Cftr^-/- tissue. Compared with wild-type mice, Cftr^-/- mice showed reduced expression of SLC26A6 in duodenum by immunofluorescence and Western blot analysis. Furthermore, coexpression of CFTR stimulated SLC26A6-mediated Cl^--oxalate exchange in Xenopus oocytes. In association with the profound defect in intestinal oxalate secretion, Cftr^-/- mice had serum and urine oxalate levels 2.5-fold greater than those of wild-type mice. We conclude that defective intestinal oxalate secretion mediated by SLC26A6 may contribute to the hyperoxaluria observed in this mouse model of cystic fibrosis. Future studies are needed to address whether similar mechanisms contribute to the increased risk for calcium oxalate stone formation observed in patients with cystic fibrosis.

Recent advances in managing and understanding nephrolithiasis/nephrocalcinosis

Urinary stone disease is a very common disease whose prevalence is still increasing. Stone formation is frequently associated with other diseases of affluence such as hypertension, osteoporosis, cardiovascular disease, metabolic syndrome, and insulin resistance. The increasing concentration of lithogenic solutes along the different segments of the nephron involves supersaturation conditions leading to the formation, growth, and aggregation of crystals. Crystalline aggregates can grow free in the tubular lumen or coated on the wall of the renal tubule. Plugs of crystalline material have been highlighted in the tubular lumen in some patients, but crystalline growth starting from plaques of calcium phosphate within the renal papillae has been demonstrated in others. Urinary supersaturation is the result of a complex interaction between predisposing genetic features and environmental factors. Dietary intake is certainly the most important environmental risk factor. In particular, an insufficient intake of dietary calcium (<600 mg/day) can increase the intestinal absorption of oxalate and the risk of calcium oxalate stone formation. Other possible risk factors that have been identified include excessive intake of salt and proteins. The potential role of dietary acid load seems to play an important role in causing a state of subclinical chronic acidosis; therefore, the intake of vegetables is encouraged in stone-forming patients. Consumption of sugar-sweetened soda and punch is associated with a higher risk of stone formation, whereas consumption of coffee, tea, beer, wine, and orange juice is associated with a lower risk. A high fluid intake is widely recognized as the cornerstone of prevention of all forms of stones. The effectiveness of protein and salt restriction has been evaluated in some studies that still do not allow definitive conclusions to be made. Calcium stone formation can be prevented by the use of different drugs with different mechanisms of action (thiazide diuretics, allopurinol, and potassium citrate), but there is no ideal drug that is both risk free and well tolerated.

Calcium intake and urinary stone disease

Calcium homeostasis is a complicated and incompletely understood process that is primarily regulated through an interaction between the intestines, kidneys, and bones. Intestinal calcium absorption is determined by many factors including the amount of regular calcium intake, as well as vitamin D and parathyroid hormone levels. Intestinal calcium absorption is likely different between stone formers and non-stone formers, with higher levels of calcium absorption in those with a history of stones independent of their calcium intake. We no longer recommend dietary calcium restriction as this may lead to bone demineralization and an increase in stone formation. Practitioners need to continue to educate patients to maintain moderate dietary calcium intake. The effect of calcium supplementation on stone formation is currently controversial. It is likely that large doses of supplemental calcium, especially if taken separate from a meal, may lead to stone formation. When necessary, stone forming patients should be encouraged to take their calcium supplements with a meal and their stone disease should be monitored.

Dietary recommendations and treatment of patients with recurrent idiopathic calcium stone disease

This review describes the various dietary regimens that have been used to advise patients on how to prevent the recurrence of their calcium-containing kidney stones. The conclusion is that although there is some general advice that may be useful to many patients, it is more efficacious to screen each patient individually to identify his/her main urinary, metabolic, nutritional, environmental, and lifestyle risk factors for stone-formation and then tailor specific advice for that particular patient based on the findings from these investigations. If the patient can be motivated to adhere strictly to this conservative approach to the prophylactic management of their stone problem over a long time period, then it is possible to prevent them from forming further stones. This approach to stone management is considerably less expensive than any of the procedures currently available for stone removal or disintegration. In the UK, for each new stone episode prevented by this conservative approach to prophylaxis it is calculated to save the Health Authority concerned around £2000 for every patient treated successfully. In the long term, this accumulates to a major saving within each hospital budget if most stone patients can be prevented from forming further stones and when the savings are totalled up country-wide saves the National Exchequer considerable sums in unclaimed Sick Pay and industry a significant number of manpower days which would otherwise be lost from work. It is also of immense relief and benefit to the patients not to have to suffer the discomfort and inconvenience of further stone episodes.

The management of patients with enteric hyperoxaluria

Enteric hyperoxaluria is a common occurrence in the setting of fat malabsorption, usually due to intestinal resection or intestinal bypass surgery. Enhanced intestinal absorption of dietary oxalate leads to elevated renal oxalate excretion, frequently in excess of 100 mg/d (1.14 mmol/d). Patients are at increased risk of urolithiasis and loss of kidney function from oxalate nephropathy. Fat malabsorption causes increased binding of diet calcium by free fatty acids, reducing the calcium available to precipitate diet oxalate. Delivery of unabsorbed bile salts and fatty acids to the colon increases colonic permeability, the site of oxalate hyper-absorption in enteric hyperoxaluria. The combination of soluble oxalate in the intestinal lumen and increased permeability of the colonic mucosa leads to hyperoxaluria. Dietary therapy consists of limiting oxalate and fat intake. The primary medical intervention is the use of oral oxalate binding agents such as calcium salts to reduce free intestinal oxalate levels. Bile acid sequestrants can be useful in patients with ileal resection and bile acid malabsorption. Oxalate degrading bacteria provided as probiotics are being investigated but as of yet, no definite benefit has been shown with currently available preparations. The current state of medical therapy and potential future directions will be summarized in this article.

Nephropathy in dietary hyperoxaluria: A potentially preventable acute or chronic kidney disease

Hyperoxaluria can cause not only nephrolithiasis and nephrocalcinosis, but also renal parenchymal disease histologically characterized by deposition of calcium oxalate crystals throughout the renal parenchyma, profound tubular damage and interstitial inflammation and fibrosis. Hyperoxaluric nephropathy presents clinically as acute or chronic renal failure that may progress to end-stage renal disease (ESRD). This sequence of events, well recognized in the past in primary and enteric hyperoxalurias, has also been documented in a few cases of dietary hyperoxaluria. Estimates of oxalate intake in patients with chronic dietary hyperoxaluria who developed chronic kidney disease or ESRD were comparable to the reported average oxalate content of the diets of certain populations worldwide, thus raising the question whether dietary hyperoxaluria is a primary cause of ESRD in these regions. Studies addressing this question have the potential of improving population health and should be undertaken, alongside ongoing studies which are yielding fresh insights into the mechanisms of intestinal absorption and renal excretion of oxalate, and into the mechanisms of development of oxalate-induced renal parenchymal disease. Novel preventive and therapeutic strategies for treating all types of hyperoxaluria are expected to develop from these studies.

Fad diets and their effect on urinary stone formation

The influence of unhealthy dietary habits on urinary stone formation has been widely recognized in literature. Dietary advice is indeed the cornerstone prescription for prevention of nephrolithiasis as well. However, only a small amount of medical literature has addressed the influence of popular or fad diets, often self-prescribed for the management of obesity and overweight or for cultural beliefs, on the risk of kidney stones. Thereby in this paper we analyze the current knowledge on the effects of some popular diets on overall lithogenic risk. High-protein diets, like Dukan diet, raise some concerns, since animal proteins are able to increase urinary calcium and to decrease urinary citrate excretion, thus leading to a high overall lithogenic risk. Low-carbohydrate diets, like Atkins diet or zone diet, may have a protective role against kidney stone formation, but there are also evidences stating that this dietary approach may rise calciuria and decrease citraturia, since it is generally associated to a relatively high intake of animal proteins. Vegan diet can be harmful for urinary stone disease, especially for the risk of hyperuricemia and micronutrient deficiencies, even if only few studies have addressed this specific matter. On the other side, the benefits of a lacto-ovo-vegetarian diet on kidney stone prevention have been largely emphasized, provided that the intake of calcium and oxalate is balanced. Traditional Mediterranean diet should exert a protective effect on nephrolithiasis as well, even if specific studies have not been carried out yet. High phytate and antioxidant content of this diet have however demonstrated to be beneficial in preventing the formation of new or recurrent calculi. Anyway, at the current state of knowledge, the most effective dietary approach to prevent kidney stone disease is a mild animal protein restriction, a balanced intake of carbohydrates and fats and a high intake of fruit and vegetables. Other fundamental aspects, which are often neglected in fad diets, are a normal intake of milk and dairy products and salt restriction. All these nutritional aspects should be greatly taken into account when patients who are willing to undergo fad or commercial diets ask for dietary advice.

Secondary hyperoxaluria: a risk factor for kidney stone formation and renal failure in native kidneys and renal grafts

Secondary hyperoxaluria is a multifactorial disease affecting several organs and tissues, among which stand native and transplanted kidneys. Nephrocalcinosis and nephrolithiasis may lead to renal insufficiency. Patients suffering from secondary hyperoxaluria, should be promptly identified and appropriately treated, so that less renal damage occurs. The aim of this review is to underline the causes of hyperoxaluria and the related pathophysiologic mechanisms, which are involved, along with the description of seven cases of irreversible renal graft injury due to secondary hyperoxaluria.

Dietary hyperoxaluria is not reduced by treatment with lactic acid bacteria

Background

Secondary hyperoxaluria either based on increased intestinal absorption of oxalate (enteric), or high oxalate intake (dietary), is a major risk factor of calcium oxalate urolithiasis. Oxalate-degrading bacteria might have beneficial effects on urinary oxalate excretion resulting from decreased intestinal oxalate concentration and absorption.

Methods

Twenty healthy subjects were studied initially while consuming a diet normal in oxalate. Study participants were then placed on a controlled oxalate-rich diet for a period of 6 weeks. Starting with week 2 of the oxalate-rich diet, participants received 2.6 g/day of a lactic acid bacteria preparation for 5 weeks. Finally, subjects were examined 4 weeks after treatment while consuming again a normal-oxalate diet. Participants provided weekly 24-hour urine specimens. Analyses of blood samples were performed before and at the end of treatment.

Results

Urinary oxalate excretion increased significantly from 0.354 ± 0.097 at baseline to 0.542 ± 0.163 mmol/24 h under the oxalate-rich diet and remained elevated until the end of treatment, as did relative supersaturation of calcium oxalate. Plasma oxalate concentration was significantly higher after 5 weeks of treatment compared to baseline. Four weeks after treatment, urinary oxalate excretion and relative supersaturation of calcium oxalate fell to reach initial values.

Conclusions

Persistent dietary hyperoxaluria and increased plasma oxalate concentration can already be induced in healthy subjects without disorders of oxalate metabolism. The study preparation neither reduced urinary oxalate excretion nor plasma oxalate concentration. The preparation may be altered to select for lactic acid bacteria strains with the highest oxalate-degrading activity.

The metabolic and ecological interactions of oxalate-degrading bacteria in the Mammalian gut

Oxalate-degrading bacteria comprise a functional group of microorganisms, commonly found in the gastrointestinal tract of mammals. Oxalate is a plant secondary compound (PSC) widely produced by all major taxa of plants and as a terminal metabolite by the mammalian liver. As a toxin, oxalate can have a significant impact on the health of mammals, including humans. Mammals do not have the enzymes required to metabolize oxalate and rely on their gut microbiota for this function. Thus, significant metabolic interactions between the mammalian host and a complex gut microbiota maintain the balance of oxalate in the body. Over a dozen species of gut bacteria are now known to degrade oxalate. This review focuses on the host-microbe and microbe-microbe interactions that regulate the degradation of oxalate by the gut microbiota. We discuss the pathways of oxalate throughout the body and the mammalian gut as a series of differentiated ecosystems that facilitate oxalate degradation. We also explore the mechanisms and functions of microbial oxalate degradation along with the implications for the ecological and evolutionary interactions within the microbiota and for mammalian hosts. Throughout, we consider questions that remain, as well as recent technological advances that can be employed to answer them.

Dietary calcium from dairy and nondairy sources, and risk of symptomatic kidney stones

PURPOSE

Because of high correlations between dairy intake and total dietary calcium, previously reported associations between lower calcium intake and increased kidney stone risk represent de facto associations between milk products and risk. We examined associations between dietary calcium from nondairy and dairy sources, and symptomatic nephrolithiasis.

MATERIALS AND METHODS

We performed prospective studies in the Health Professionals Follow-up Study (HPFS) in 30,762 men, and in the Nurses' Health Study (NHS) I and II in 94,164 and 101,701 women, respectively. We excluded men 60 years old or older because we previously reported inverse associations between calcium intake and risk only in men younger than 60 years. Food frequency questionnaires were used to assess calcium intake every 4 years. We used Cox proportional hazards regression to adjust for age, body mass index, supplemental calcium, diet and other factors.

RESULTS

We documented 5,270 incident kidney stones during the combined 56 years of followup. In participants in the highest vs the lowest quintile of nondairy dietary calcium the multivariate relative risk of kidney stones was 0.71 (95% CI 0.56-0.92, p for trend 0.007) in HPFS, 0.82 (95% CI 0.69-0.98, p trend 0.08) in NHS I and 0.74 (95% CI 0.63-0.87, p trend 0.002) in NHS II. When comparing the highest to the lowest quintile of dairy calcium, the multivariate relative risk was 0.77 (95% CI 0.63-0.95, p trend 0.01) for HPFS, 0.83 (95% CI 0.69-0.99, p trend 0.05) for NHS I and 0.76 (95% CI 0.65-0.88, p trend 0.001) for NHS II.

CONCLUSIONS

Higher dietary calcium from nondairy or dairy sources is independently associated with a lower kidney stone risk.

Kidney stones: an update on current pharmacological management and future directions

INTRODUCTION

Kidney stones are a common problem worldwide with substantial morbidities and economic costs. Medical therapy reduces stone recurrence significantly. Much progress has been made in the last several decades in improving therapy of stone disease.

AREAS COVERED

This review discusses i) the effect of medical expulsive therapy on spontaneous stone passage, ii) pharmacotherapy in the prevention of stone recurrence and iii) future directions in the treatment of kidney stone disease.

EXPERT OPINION

Fluid intake to promote urine volume of at least 2.5 L each day is essential to prevent stone formation. Dietary recommendations should be adjusted based on individual metabolic abnormalities. Properly dosed thiazide treatment is the standard therapy for calcium stone formers with idiopathic hypercalciuria. Potassium alkali therapy is considered for hypocitraturia, but caution should be taken to prevent potential risk of calcium phosphate stone formation. For absorptive hyperoxaluria, low oxalate diet and increased dietary calcium intake are recommended. Pyridoxine has been shown effective in some cases of primary hyperoxaluria type I. Allopurinol is used in calcium oxalate stone formers with hyperuricosuria. Treatment of cystine stones remains challenging. Tiopronin can be used if urinary alkalinization and adequate fluid intake are insufficient. For struvite stones, complete surgical removal coupled with appropriate antibiotic therapy is necessary.

NALP3-mediated inflammation is a principal cause of progressive renal failure in oxalate nephropathy

Oxalate nephropathy with renal failure is caused by multiple disorders leading to hyperoxaluria due to either overproduction of oxalate (primary hyperoxaluria) or excessive absorption of dietary oxalate (enteric hyperoxaluria). To study the etiology of renal failure in crystal-induced kidney disease, we created a model of progressive oxalate nephropathy by feeding mice a diet high in soluble oxalate (high oxalate in the absence of dietary calcium). Renal histology was characterized by intratubular calcium-oxalate crystal deposition with an inflammatory response in the surrounding interstitium. Oxalate nephropathy was not found in mice fed a high oxalate diet that also contained calcium. NALP3, also known as cryopyrin, has been implicated in crystal-associated diseases such as gout and silicosis. Mice fed the diet high in soluble oxalate demonstrated increased NALP3 expression in the kidney. Nalp3-null mice were completely protected from the progressive renal failure and death that occurred in wild-type mice fed the diet high in soluble oxalate. NALP3 deficiency did not affect oxalate homeostasis, thereby excluding differences in intestinal oxalate handling to explain the observed phenotype. Thus, progressive renal failure in oxalate nephropathy results primarily from NALP3-mediated inflammation.

Pharmacologic treatment of kidney stone disease

This article reviews the data on pharmacologic treatment of kidney stone disease, with a focus on prophylaxis against stone recurrence. One of the most effective and important therapies for stone prevention, an increase in urine volume, is not discussed because this is a dietary and not a pharmacologic intervention. Also reviewed are medical expulsive therapy used to improve the spontaneous passage of ureteral stones and pharmacologic treatment of symptoms associated with ureteral stents. The goal is to review the literature with a focus on the highest level of evidence (ie, randomized controlled trials).

Calcium metabolism and correcting calcium deficiencies

Calcium is the most abundant cation in the human body, of which approximately 99% occurs in bone, contributing to its rigidity and strength. Bone also functions as a reservoir of Ca for its role in multiple physiologic and biochemical processes. This article aims to provide a thorough understanding of the absorptive mechanisms and factors affecting these processes to enable one to better appreciate an individual's Ca needs, and to provide a rationale for correcting Ca deficiencies. An overview of Ca requirements and suggested dosing regimens is presented, with discussion of various Ca preparations and potential toxicities of Ca treatment.

Hyperoxaluria: a gut-kidney axis?

Hyperoxaluria leads to urinary calcium oxalate (CaOx) supersaturation, resulting in the formation and retention of CaOx crystals in renal tissue. CaOx crystals may contribute to the formation of diffuse renal calcifications (nephrocalcinosis) or stones (nephrolithiasis). When the innate renal defense mechanisms are suppressed, injury and progressive inflammation caused by these CaOx crystals, together with secondary complications such as tubular obstruction, may lead to decreased renal function and in severe cases to end-stage renal failure. For decades, research on nephrocalcinosis and nephrolithiasis mainly focused on both the physicochemistry of crystal formation and the cell biology of crystal retention. Although both have been characterized quite well, the mechanisms involved in establishing urinary supersaturation in vivo are insufficiently understood, particularly with respect to oxalate. Therefore, current therapeutic strategies often fail in their compliance or effectiveness, and CaOx stone recurrence is still common. As the etiology of hyperoxaluria is diverse, a good understanding of how oxalate is absorbed and transported throughout the body, together with a better insight in the regulatory mechanisms, is crucial in the setting of future treatment strategies of this disorder. In this review, the currently known mechanisms of oxalate handling in relevant organs will be discussed in relation to the different etiologies of hyperoxaluria. Furthermore, future directions in the treatment of hyperoxaluria will be covered.

DASH-style diet and 24-hour urine composition

BACKGROUND AND OBJECTIVES

We previously observed associations between a Dietary Approaches to Stop Hypertension (DASH)-style diet and large reductions in kidney stone risk. This study examined associations between a DASH-style diet and 24-hour excretions of urinary lithogenic factors.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We studied 3426 participants with and without nephrolithiasis in the Health Professionals Follow-up Study (HPFS) and the Nurses' Health Studies (NHS) I and II. A dietary DASH score was based on seven components: high intake of fruits, vegetables, nuts and legumes, dairy products, and whole grains and low intake of sweetened beverages and red and processed meats. We used analysis of covariance to adjust for age, stone history, body size, and other factors.

RESULTS

Comparing participants in the highest to lowest quintiles of DASH score, multivariate-adjusted urinary calcium excretion was 3% greater in HPFS (P trend 0.12), 10% greater in NHS I (P trend <0.01), and 12% greater in NHS II (P trend 0.05). Urinary oxalate was 4% to 18% greater (P trend all ≤0.03), urinary citrate was 11% to 16% greater (P trend all <0.01), and urinary volume was 16% to 32% greater (P trend all <0.001). Higher DASH score was associated with higher urine potassium, magnesium, phosphate, and pH, and lower relative supersaturations (RSS) of calcium oxalate (women only) and uric acid.

CONCLUSIONS

A DASH-style diet may reduce stone risk by increasing urinary citrate and volume. The small associations between higher DASH score and lower RSS suggest unidentified stone inhibitors in dairy products and/or plants.

DASH-style diet associates with reduced risk for kidney stones

The impact of the Dietary Approaches to Stop Hypertension (DASH) diet on kidney stone formation is unknown. We prospectively examined the relation between a DASH-style diet and incident kidney stones in the Health Professionals Follow-up Study (n = 45,821 men; 18 yr of follow-up), Nurses' Health Study I (n = 94,108 older women; 18 yr of follow-up), and Nurses' Health Study II (n = 101,837 younger women; 14 yr of follow-up). We constructed a DASH score based on eight components: high intake of fruits, vegetables, nuts and legumes, low-fat dairy products, and whole grains and low intake of sodium, sweetened beverages, and red and processed meats. We used Cox hazards regression to adjust for factors that included age, BMI, and fluid intake. Over a combined 50 yr of follow-up, we documented 5645 incident kidney stones. Participants with higher DASH scores had higher intakes of calcium, potassium, magnesium, oxalate, and vitamin C and had lower intakes of sodium. For participants in the highest compared with the lowest quintile of DASH score, the multivariate relative risks for kidney stones were 0.55 (95% CI, 0.46 to 0.65) for men, 0.58 (95% CI, 0.49 to 0.68) for older women, and 0.60 (95% CI, 0.52 to 0.70) for younger women. Higher DASH scores were associated with reduced risk even in participants with lower calcium intake. Exclusion of participants with hypertension did not change the results. In conclusion, consumption of a DASH-style diet is associated with a marked decrease in kidney stone risk.

Diet to reduce mild hyperoxaluria in patients with idiopathic calcium oxalate stone formation: a pilot study

OBJECTIVES

To assess whether a normal-calcium, low-animal protein, low-salt diet is effective in reducing hyperoxaluria in idiopathic calcium oxalate nephrolithiasis compared with a traditional low-oxalate diet, routinely recommended by clinicians

METHODS

We treated 56 patients with idiopathic calcium oxalate stone formation who presented with mild hyperoxaluria (>40 mg/d) while consuming a free diet with a normal-calcium, low-animal protein, low-salt diet for a 3-month period. We compared the results obtained with this diet with those of a historical control group of 20 hyperoxaluric patients treated in the traditional way with a low-oxalate diet

RESULTS

After 3 months of therapy, the mean oxaluria level had decreased from 50.2 to 35.5 mg/d with the normal-calcium, low-animal protein, low-salt diet and from 45.9 to 40.2 mg/d with the traditional diet (adjusted difference between post-treatment mean value -7.3 mg/d, 95% confidence interval -12.3 to -2.2, P = .005)

CONCLUSIONS

The results suggest that a normal-calcium, low-animal protein, low-salt diet can reduce oxalate excretion in hyperoxaluric patients. This should encourage the undertaking of a randomized-control study to confer more solid evidence in support of our findings.

Determinants of 24-hour urinary oxalate excretion

BACKGROUND AND OBJECTIVES

Higher levels of urinary oxalate substantially increase the risk of calcium oxalate kidney stones. However, the determinants of urinary oxalate excretion are unclear. The objective was to examine the impact of dietary factors, age, body size, diabetes, and urinary factors on 24-h urinary oxalate.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

We conducted a cross-sectional study of 3348 stone forming and non-stone-forming participants in the Health Professionals Follow-up Study (men), the Nurses' Health Study (older women), and the Nurses' Health Study II (younger women).

RESULTS

Median urinary oxalate was 39 mg/d in men, 27 mg/d in older women, and 26 mg/d in younger women. Participants in the highest quartile of dietary oxalate excreted 1.7 mg/d more urinary oxalate than participants in the lowest quartile (P trend 0.001). The relation between dietary and urinary oxalate was similar in individuals with and without nephrolithiasis. Participants consuming 1000 mg/d or more of vitamin C excreted 6.8 mg/d more urinary oxalate than participants consuming <90 mg/d (P trend < 0.001). Body mass index, total fructose intake, and 24-h urinary potassium, magnesium, and phosphorus levels also were positively associated with urinary oxalate. Calcium intake and age were inversely associated with urinary oxalate. After adjustment for body size, participants with diabetes excreted 2.0 mg/d more urinary oxalate than those without diabetes (P < 0.01).

CONCLUSIONS

The impact of dietary oxalate on urinary oxalate appears to be small. Further investigation of factors influencing urinary oxalate may lead to new approaches to prevent calcium kidney stones.

Oxalate intake and the risk for nephrolithiasis

Most kidney stones consist of calcium oxalate, and higher urinary oxalate increases the risk for calcium oxalate nephrolithiasis. However, the relation between dietary oxalate and stone risk is unclear. This study prospectively examined the relation between oxalate intake and incident nephrolithiasis in the Health Professionals Follow-up Study (n = 45,985 men), the Nurses' Health Study I (n = 92,872 older women), and the Nurses' Health Study II (n = 101,824 younger women). Food frequency questionnaires were used to assess oxalate intake every 4 yr. Cox proportional hazards regression was used to adjust for age, body mass index, thiazide use, and dietary factors. A total of 4605 incident kidney stones were documented over a combined 44 yr of follow-up. Mean oxalate intakes were 214 mg/d in men, 185 mg/d in older women, and 183 mg/d in younger women and were similar in stone formers and non-stone formers. Spinach accounted for >40% of oxalate intake. For participants in the highest compared with lowest quintile of dietary oxalate, the relative risks for stones were 1.22 (95% confidence interval [CI] 1.03 to 1.45; P = 0.01 for trend) for men and 1.21 (95% CI 1.01 to 1.44; P = 0.05 for trend) for older women. Risk was higher in men with lower dietary calcium (P = 0.08 for interaction). The relative risks for participants who ate eight or more servings of spinach per month compared with fewer than 1 serving per month were 1.30 (95% CI 1.08 to 1.58) for men and 1.34 (95% CI 1.10 to 1.64) for older women. Oxalate intake and spinach were not associated with risk in younger women. These data do not implicate dietary oxalate as a major risk factor for nephrolithiasis.

Prevention of Stone Disease

In recent years stone disease has become more widespread in developed countries. At present the prevalence is 5.2 and 15% of men and 6% of women are affected. The increase is linked to changes in lifestyle, eating patterns and obesity which has become very common. The 'metabolic syndrome' includes all the diseases, e.g. hypertension, lipid imbalances, type 2 diabetes mellitus, gout and cardiovascular disease, which are concomitant in the majority of stone formers. Dietary patterns, besides leading to stone formation, also determine stone chemistry. With a diet that is rich in oxalates, calcium oxalate will constitute 75% of stones, struvite 10-20%, uric acid 5-6% and cystine 1%. As approximately 50% of patients with stones suffer recurrences, metabolic and/or pharmacological prophylaxis is recommended.