Diet and renal stones in 72 areas in England and Wales

Ambient temperature as a contributor to kidney stone formation: implications of global warming

Nephrolithiasis is a common disease across the world that is becoming more prevalent. Although the underlying cause for most stones is not known, a body of literature suggests a role of heat and climate as significant risk factors for lithogenesis. Recently, estimates from computer models predicted up to a 10% increase in the prevalence rate in the next half century secondary to the effects of global warming, with a coinciding 25% increase in health-care expenditures. Our aim here is to critically review the medical literature relating stones to ambient temperature. We have categorized the body of evidence by methodology, consisting of comparisons between geographic regions, comparisons over time, and comparisons between people in specialized environments. Although most studies are confounded by other factors like sunlight exposure and regional variation in diet that share some contribution, it appears that heat does play a role in pathogenesis in certain populations. Notably, the role of heat is much greater in men than in women. We also hypothesize that the role of a significant human migration (from rural areas to warmer, urban locales beginning in the last century and projected to continue) may have a greater impact than global warming on the observed worldwide increasing prevalence rate of nephrolithiasis. At this time the limited data available cannot substantiate this proposed mechanism but further studies to investigate this effect are warranted.

Épidémiologie actuelle de la lithiase rénale en France

Nephrolithiasis is a frequent disease that affects about 10% of people in western countries. The prevalence of calcium oxalate stones has been constantly increasing during the past fifty years in France as well as in other industrialized countries. Stone composition varies depending to gender and age of patients and also underlines the role of other risk factors and associated pathologies such as body mass index and diabetes mellitus. The decrease in struvite frequency in female patients is the result of a significantly improved diagnostic and treatment of urinary tract infections by urea-splitting bacteria. In contrast, the increasing occurrence of weddellite calculi in stone forming women aged more than 50 years could be the consequence of post-menopausal therapy. A high prevalence of uric acid was found in overweight and obese stone formers and in diabetic ones as well. Another important finding was the increased occurrence with time of calcium oxalate stones formed from papillary Randall's plaques, especially in young patients. Nutritional risk factors for stone disease are well known: they include excessive consumption of animal proteins, sodium chloride and rapidly absorbed glucides, and insufficient dietary intake of fruits and potassium-rich vegetables, which provide an alkaline load. As a consequence, an excessive production of hydrogen ions may induce several urinary disorders including low urine pH, high urine calcium and uric acid excretion and low urine citrate excretion. Excess in calorie intake, high chocolate consumption inducing hyperoxaluria and low water intake are other factors, which favour excessive urine concentration of solutes. Restoring the dietary balance is the first advice to prevent stone recurrence. However, the striking increase of some types of calculi, such as calcium oxalate stones developed from Randall's plaque, should alert to peculiar lithogenetic risk factors and suggests that specific advices should be given to prevent stone formation.

Effects of low animal protein or high-fiber diets on urine composition in calcium nephrolithiasis

BACKGROUND

The purpose of this article is to evaluate the impact of low protein and high fiber intakes on risk factors of stone recurrence in idiopathic calcium stone formers (ICSFs).

METHODS

Ninety-six ICSFs were randomly assigned a low animal protein diet (< 10% of total energy), a high-fiber diet (> 25 g/day), or a usual diet (control group); all patients were recommended to increase their fluid intake. Their daily urine compositions were analyzed at baseline and at four months. Compliance with dietary recommendations was checked by validated food frequency questionnaires. Compliance with total and animal protein intakes was assessed by 24-hour urea and sulfate outputs, respectively. The nutritional intervention (oral instructions, written leaflet, phoning) and food assessment were carried out by a research dietitian.

RESULTS

At baseline, diets and the daily urine composition did not differ between the three groups. At four months, while diets differed significantly, the 24-hour output of calcium and oxalate did not differ significantly within and between groups after adjustment for potential confounders (age, sex, and personal and family history of calcium stones) and baseline values. However, as many as 12 out of 31 ICSFs (95% CI, 22 to 58%) assigned to a low animal protein diet achieved a reduction in the urine urea excretion rate of more than 50 mmol/day and also exhibited a significant decrease in urinary calcium excretion that averaged 1.8 mmol/day. A significant correlation between urea and calcium outputs was observed only among patients with hypercalciuria.

CONCLUSIONS

These results show that only ICSFs who markedly decrease their animal protein intake, especially those with hypercalciuria, can expect to benefit from dietary recommendations.

Oxalate transport and calcium oxalate renal stone disease

Hyperoxaluria is considered to play a crucial role in calcium oxalate (CaOx) renal stone disease. The amount of oxalate excreted into the urine depends on intestinal absorption, endogenous production, renal clearance and renal tubular transport. Since a primary disorder has not been found so far in most CaOx stone formers and since oxalate is freely filtered at the glomerulus, most studies are presently focussed on alterations in epithelial oxalate transport pathways. Oxalate can be transported across an epithelium by the paracellular (passive) and transcellular (active) pathway. Oxalate transport across cellular membranes is mediated by anion-exchange transport proteins. A defect in the structure of these transport proteins could explain augmented transcellular oxalate transport. Little is known about the physiological regulation of oxalate transport. In this review cellular transport systems for oxalate will be summarized with special attention for the progress that has been made to study oxalate transport in a model of cultured renal tubule cells. Better understanding of the physiological processes that are involved in oxalate transport could yield information on the basis of which it might be possible to design new approaches for an effective treatment of CaOx stone disease.

Oxalate transport and calcium oxalate renal stone disease

Hyperoxaluria is considered to play a crucial role in calcium oxalate (CaOx) renal stone disease. The amount of oxalate excreted into the urine depends on intestinal absorption, endogenous production, renal clearance and renal tubular transport. Since a primary disorder has not been found so far in most CaOx stone formers and since oxalate is freely filtered at the glomerulus, most studies are presently focussed on alterations in epithelial oxalate transport pathways. Oxalate can be transported across an epithelium by the paracellular (passive) and transcellular (active) pathway. Oxalate transport across cellular membranes is mediated by anion-exchange transport proteins. A defect in the structure of these transport proteins could explain augmented transcellular oxalate transport. Little is known about the physiological regulation of oxalate transport. In this review cellular transport systems for oxalate will be summarized with special attention for the progress that has been made to study oxalate transport in a model of cultured renal tubule cells. Better understanding of the physiological processes that are involved in oxalate transport could yield information on the basis of which it might be possible to design new approaches for an effective treatment of CaOx stone disease.

Dietary effects upon calcium oxalate urolithiasis risk

An animal model involving rats fed with different diets (high protein, high carbohydrate, high lipid, high fiber and control balanced diet) was used to evaluate the dietary effects on the main oxalocalcic urolithogenic parameters. It was found that the inhibitory factors that prevent calcium oxalate stone formation (citrate and magnesium) were clearly more favorable in the group of rats fed with a balanced diet. However, factors favouring the heterogeneous calcium phosphate nucleation were also found in the balanced diet. On the other hand, factors facilitating the heterogeneous uric acid nucleation were found in rats treated with high protein, high lipid, high carbohydrate and high fiber diets. In conclusion it seems that the balanced diet appears to be the less lithogenic one.

An animal model to study the effects of diet on risk factors of calcium stone formation

The effects of diet on the formation of calcium oxalate stones were studied in 150-day-old rats by measuring the diuresis, pH, and urinary and blood concentrations of promoting and inhibitory substances. An increase in phosphate (promoting) and magnesium (inhibiting), and a decrease in citrate (inhibiting) and pH were found in the urine of rats fed with a high protein diet. No differences were observed in the plasma concentrations of calcium, magnesium, and phosphate. These results confirm epidemiological and clinical studies in humans that have shown that any diet rich in protein can change the concentrations of these substances in urine.