Risk Of Incident Kidney Stones Research Articles

Total, Dietary, and Supplemental Vitamin C Intake and Risk of Incident Kidney Stones

Previous studies of vitamin C and kidney stones were conducted mostly in men and either reported disparate results for supplemental and dietary vitamin C or did not examine dietary vitamin C. Prospective cohort analysis. 156,735 women in the Nurses' Health Study (NHS) I and II and 40,536 men in the Health Professionals Follow-up Study (HPFS). Total, dietary, and supplemental vitamin C intake, adjusted for age, body mass index, thiazide use, and dietary factors. Incident kidney stones. During a median follow-up of 11.3 to 11.7 years, 6,245 incident kidney stones were identified. After multivariable adjustment, total vitamin C intake (<90 [reference], 90-249, 250-499, 500-999, and ≥1,000mg/d) was not significantly associated with risk for kidney stones among women, but was among men (HRs of 1.00 [reference], 1.19 [95% CI, 0.99-1.46], 1.15 [95% CI, 0.93-1.42], 1.29 [95% CI, 1.04-1.60], and 1.43 [95% CI, 1.15-1.79], respectively; P for trend = 0.005). Median total vitamin C intake for the 500- to 999-mg/d category was ∼700mg/d. Supplemental vitamin C intake (no use [reference], <500, 500-999, and ≥1,000mg/d) was not significantly associated with risk for kidney stones among women, but was among men (HR, 1.19 [95% CI, 1.01-1.40] for ≥1,000mg/d; P for trend = 0.001). Dietary vitamin C intake was not associated with stones among men or women, although few participants had dietary intakes > 700mg/d. Nutrient intakes derived from food-frequency questionnaires, lack of data on stone composition for all cases. Total and supplemental vitamin C intake was significantly associated with higher risk for incident kidney stones in men, but not in women.

Treatment effect, adherence, and safety of high fluid intake for the prevention of incident and recurrent kidney stones: a systematic review and meta-analysis.

The objective of this systematic review and meta-analysis were to evaluate the effectiveness of high fluid intake for the prevention of incident and recurrent kidney stones, as well as its adherence and safety. A literature search was performed encompassing 1980 through July 2014. Studies that reported relative risks, odds ratios, or hazard ratios comparing the risk of kidney stone events in patients with high vs inadequate fluid intake were included. Pooled risk ratios (RRs) and 95 % confidence intervals (CIs) were calculated using a random-effect, generic inverse variance method. Nine studies [2 randomized controlled trials (RCTs) with 269 patients; 7 observational studies with 273,685 individuals] were included in the meta-analysis. Pooled RRs of kidney stones in individuals with high-fluid intake were 0.40 (95 % CI 0.20-0.79) and 0.49 (0.34-0.71) in RCTs and observational studies, respectively. High fluid intake was significantly associated with reduced risk of recurrent kidney stones: RRs 0.40 (95 % CI 0.20-0.79) and 0.20 (0.09-0.44) in RCTs and observational studies, respectively. Adherence and safety data on high fluid intake treatment were limited; 1 RCT reported no withdrawals due to adverse events. This analysis demonstrated a significantly reduced risk of incident kidney stones among individuals with high fluid consumption. High fluid consumption also reduced the risk of recurrent kidney stones. Furthermore, the magnitude of risk reduction was high. Although increased water intake appears to be safe, future studies on its safety in patients with high risk of volume overload or hyponatremia may be indicated.

Caffeine intake and the risk of kidney stones

Although caffeine intake may increase urine calcium excretion, caffeine-containing beverages have been associated with a lower risk of nephrolithiasis. We sought to determine the association between caffeine intake and the risk of incident kidney stones in 3 large prospective cohorts. We prospectively analyzed the association between intake of caffeine and incidence of kidney stones in 3 large ongoing cohort studies, the Health Professionals Follow-Up Study (HPFS) and the Nurses' Health Studies (NHS) I and II. Information on the consumption of caffeine and the incidence of kidney stones was collected by validated questionnaires. The analysis included 217,883 participants; over a median follow-up of >8 y, 4982 incident cases occurred. After multivariate adjustment for age, BMI, fluid intake, and other factors, participants in the highest quintile of caffeine intake had a 26% (95% CI: 12%, 38%) lower risk of developing stones in the HPFS cohort, a 29% lower risk (95% CI: 15%, 41%) in the NHS I cohort, and a 31% lower risk (95% CI: 18%, 42%) in the NHS II cohort (P-trend < 0.001 for all cohorts). The association remained significant in the subgroup of participants with a low or no intake of caffeinated coffee in the HPFS cohort. Among 6033 participants with 24-h urine data, the intake of caffeine was associated with higher urine volume, calcium, and potassium and with lower urine oxalate and supersaturation for calcium oxalate and uric acid. Caffeine intake is independently associated with a lower risk of incident kidney stones.

Physical Activity, Energy Intake and the Risk of Incident Kidney Stones

Recent data suggest that higher physical activity and lower energy intake may be associated with a lower risk of kidney stones. To our knowledge whether these associations could be reproduced in other study populations after accounting for life-style and dietary factors is not known. We analyzed data on 3 large prospective cohorts, including HPFS, and NHS I and II. Information was collected by validated biennial questionnaires. The HR of incident stones in participants in different categories of physical activity and energy intake was assessed by Cox proportion hazards regression adjusted for age, body mass index, race, comorbidity, medication, calcium supplement use, fluid and nutrient intake. Analysis included 215,133 participants. After up to 20 years of followup 5,355 incident cases of kidney stones occurred. On age adjusted analysis higher levels of physical activity were associated with a lower risk of incident kidney stones in women (NHS I and II) but not in men. However, after multivariate adjustment there was no significant association between physical activity and kidney stone risk in HPFS, and NHS I and II (highest vs lowest category HR 1.00, 95% CI 0.87-1.14, p for trend = 0.94, HR 1.01, 95% CI 0.85-1.19, p for trend = 0.88 and HR 1.03, 95% CI 0.90-1.18, p for trend = 0.64, respectively). Energy intake was not associated with stone risk (multivariate adjusted p for trend ≥0.49). In 3 large prospective cohorts there was no independent association between physical activity and energy intake, and the incidence of symptomatic kidney stones.

Dietary Intake of Fiber, Fruit and Vegetables Decreases the Risk of Incident Kidney Stones in Women: A Women’s Health Initiative Report

We evaluated the relationship between dietary fiber, fruit and vegetable intake, and the risk of kidney stone formation. Overall 83,922 postmenopausal women from the Women's Health Initiative observational study were included in the analysis and followed prospectively. Cox proportional hazards regression analyses were used to evaluate the associations between total dietary fiber, fruit and vegetable intake, and the risk of incident kidney stone formation, adjusting for nephrolithiasis risk factors (age, race/ethnicity, geographic region, diabetes mellitus, calcium supplementation, hormone therapy use, body mass index and calibrated caloric intake; and dietary water, sodium, animal protein and calcium intake). Women with a history of kidney stones (3,471) were analyzed separately. Mean age of the women was 64±7 years, 85% were white and 2,937 (3.5%) experienced a kidney stone in a median followup of 8 years. In women with no history of kidney stones higher total dietary fiber (6% to 26% decreased risk, p <0.001), greater fruit intake (12% to 25% decreased risk, p <0.001) and greater vegetable intake (9% to 22% decreased risk, p=0.002) were associated with a decreased risk of incident kidney stone formation in separate adjusted models. In women with a history of stones there were no significant protective effects of fiber, fruit or vegetable intake on the risk of kidney stone recurrence. Greater dietary intake of fiber, fruits and vegetables was associated with a reduced risk of incident kidney stones in postmenopausal women. The protective effects were independent of other known risk factors for kidney stones. In contrast, there was no reduction in risk in women with a history of stones.

Activity, Energy Intake, Obesity, and the Risk of Incident Kidney Stones in Postmenopausal Women

Obesity is a strong risk factor for nephrolithiasis, but the role of physical activity and caloric intake remains poorly understood. We evaluated this relationship in 84,225 women with no history of stones as part of the Women's Health Initiative Observational Study, a longitudinal, prospective cohort of postmenopausal women enrolled from 1993 to 1998 with 8 years' median follow-up. The independent association of physical activity (metabolic equivalents [METs]/wk), calibrated dietary energy intake, and body mass index (BMI) with incident kidney stone development was evaluated after adjustment for nephrolithiasis risk factors. Activity intensity was evaluated in stratified analyses. Compared with the risk in inactive women, the risk of incident stones decreased by 16% in women with the lowest physical activity level (adjusted hazard ratio [aHR], 0.84; 95% confidence interval [95% CI], 0.74 to 0.97). As activity increased, the risk of incident stones continued to decline until plateauing at a decrease of approximately 31% for activity levels ≥10 METs/wk (aHR, 0.69; 95% CI, 0.60 to 0.79). Intensity of activity was not associated with stone formation. As dietary energy intake increased, the risk of incident stones increased by up to 42% (aHR, 1.42; 95% CI, 1.02 to 1.98). However, intake <1800 kcal/d did not protect against stone formation. Higher BMI category was associated with increased risk of incident stones. In summary, physical activity may reduce the risk of incident kidney stones in postmenopausal women independent of caloric intake and BMI, primarily because of the amount of activity rather than exercise intensity. Higher caloric intake further increases the risk of incident stones.

Impact of Nutritional Factors on Incident Kidney Stone Formation: A Report From the WHI OS

Increased fluid intake, and decreased dietary sodium and animal protein intake are thought to reduce the risk of kidney stones but the role of calcium intake is controversial. We evaluated the relationship between dietary factors and incident kidney stone formation. Secondary analysis was done of 78,293 women from the prospective WHI OS (Women's Health Initiative Observational Study) with no history of nephrolithiasis who completed the validated food frequency questionnaire. Multivariate logistic regression was used to determine demographic and dietary factors, and supplement use independently associated with incident kidney stones. Overall 1,952 women (2.5%) reported an incident kidney stone in 573,575 person-years of followup. The risk of incident kidney stones was decreased by 5% to 28% (p = 0.01) with higher dietary calcium intake and by 13% to 31% (p = 0.002) with higher water intake after adjusting for nephrolithiasis risk factors. Conversely higher dietary sodium intake increased the risk of nephrolithiasis by 11% to 61% (p <0.001) after adjustment with the most pronounced effect in women with the highest intake. Higher body mass index independently increased the risk of incident nephrolithiasis (adjusted OR 1.19-2.01, p <0.001). Animal protein intake was not associated with nephrolithiasis on multivariate analysis. This study adds to the growing evidence underscoring the importance of maintaining adequate fluid and dietary calcium intake. Greater dietary calcium intake significantly decreased the risk of incident kidney stones. In contrast, excess sodium intake increased the risk of incident nephrolithiasis, especially in women with the highest intake. Animal protein intake was not independently associated with nephrolithiasis.

Cholelithiasis and the Risk of Nephrolithiasis

Existing data on the relation between gallstones and kidney stones are provocative but limited. Therefore, we determined whether symptomatic radiographically confirmed gallstones (and/or cholecystectomy) and symptomatic kidney stone disease are independently associated. We conducted cross-sectional and prospective analyses in the Nurses' Health Studies I and II (older and younger women, respectively) and the Health Professionals Follow-Up Study (men) that included more than 240,000 participants followed for 14 to 24 years. Regression models adjusted for age, body size, thiazide use, diet and other factors. At baseline the multivariate odds ratio of kidney stone history in individuals with gallstone history compared to those without was 1.65 (95% CI 1.46-1.86) in older women, 1.85 (95% CI 1.65-2.07) in younger women and 1.61 (95% CI 1.41-1.85) in men. Prospectively, the multivariate relative risk of incident kidney stones in participants with gallstone history compared to those without was 1.26 (95% CI 1.09-1.44) in older women, 1.32 (95% CI 1.14-1.52) in younger women and 1.28 (95% CI 1.03-1.57) in men. The multivariate relative risk of incident gallstones in participants with kidney stone history compared to those without was 1.17 (95% CI 1.06-1.29) in older women, 1.31 (95% CI 1.19-1.45) in younger women and 1.51 (95% CI 1.35-1.68) in men. Prospective lag analyses instituting a delay of 4 years between the diagnoses of gallstones and kidney stones yielded similar results. Gallstones and kidney stones are independently associated. Additional studies are needed to identify shared mechanisms underlying both diseases.

Cost-Effectiveness of Primary Prevention Strategies for Nephrolithiasis

Stone disease is a highly prevalent condition associated with substantial cost and morbidity. We evaluated the cost-effectiveness of a primary prevention strategy. A decision analysis model was constructed to compare the cost of ad hoc management of symptomatic stones vs the cost of primary prevention. A literature search was performed to determine the incidence of stone disease, the effectiveness of nonmedical prevention strategies and cost associated with stone management. One and 2-way sensitivity analyses were performed to determine conditions under which a strategy of primary prevention might be cost-effective. Assuming a 1% incidence of stones, a 50% risk reduction and a $100 cost per individual per year for primary prevention, the model was used to calculate the overall costs per individual per year without and with a primary prevention strategy of $46 and $123, respectively. One-way sensitivity analyses indicated that primary prevention was cost-effective if the incidence of stones exceeded 4.3% yearly or the cost of prevention was less than $23 per person yearly. Varying other factors (risk reduction, probability of requiring surgery, hours of lost work, emergency room cost) failed to reach cost equivalence under any circumstances or required unrealistic assumptions. Preventive strategies were more costly than no prevention unless the incidence of stone disease was at least 1%, the cost did not exceed $20 per person per year and the prevention strategy was at least 50% effective in preventing stones. Primary prevention strategies for stone disease have not been sufficiently evaluated but can theoretically be cost-effective if the population has a sufficiently high incidence of stone disease and the strategy is of low cost and moderately effective.

Testosterone and Androgen Receptor in Human Nephrolithiasis

We investigated the relationship of kidney calculi with plasma free and total testosterone, and androgen receptor up-regulation in the kidneys of men with nephrolithiasis. Male patients with kidney stone and healthy men were included in the study. Blood was collected in a tube containing 2% heparin in the morning. Total and free serum testosterone was measured by enzyme linked immunosorbent assay. All patients underwent percutaneous nephrostolithotomy. At the end of the procedure ultrasound guided puncture biopsy was done to acquire kidney tissue. Normal kidney tissue obtained at autopsy served as the control. Androgen receptor was detected in kidney tissue by immunohistochemistry. Stone composition was analyzed in each patient. The study included 37 male patients 22 to 39 years old and 31 healthy men 24 to 37 years old. All calculi were composed of calcium oxalate monohydrate or calcium oxalate dihydrate and a few also contained protein or uric acid. Mean±SD serum total and free testosterone was 13.29±4.79 ng/ml and 63.23±28.58 pg/ml in patients, and 7.30±0.82 ng/ml and 35.59±24.91 pg/ml in healthy men, respectively (each p<0.001). Immunohistochemistry revealed androgen receptor up-regulation in the kidneys of patients with nephrolithiasis. Our data suggest the important role of enhanced androgen signaling in human nephrolithiasis.

Impact of Urine Sodium on Urine Risk Factors for Calcium Oxalate Nephrolithiasis

Increased sodium intake is thought to promote nephrolithiasis by dietary sodium hypercalciuric effects. However, equivocal data exist on whether increased urine sodium actually increases the nephrolithiasis risk. We examined the relationship between urine sodium and urine risk factors for nephrolithiasis. We retrospectively reviewed the records of 880 patients evaluated at a metabolic stone clinic to determine the relationship between urine sodium and urine calcium, volume and calcium oxalate supersaturation. Patients were separated into sodium excretion quintiles. Tests of linear trend were performed by examining the linear contrast in coefficients and using Cuzick's nonparametric linear trend test. Multivariate linear regression with urine sodium as a continuous variable was done to assess the relationship between urine sodium and other urine variables. Tests of linear trend showed that urine calcium and volume increased with increasing urine sodium (each p <0.01) but urine calcium oxalate supersaturation decreased with increasing urine sodium (p <0.01). Multivariate linear regression was adjusted for age, sex, body mass index and urine constituents. Urine sodium was positively associated with urine calcium (beta = 0.28, 95% CI 0.15 to 0.41, p <0.001) but negatively associated with urine calcium oxalate supersaturation (beta = -0.013, 95% CI -0.016 to -0.011, p <0.001). There was a trend toward a positive association of urine sodium and volume (beta = 0.001, 95% CI -0.00019 to 0.002, p = 0.10). Increasing urine sodium does not appear to increase the risk of calcium oxalate nephrolithiasis. Global sodium restriction may not necessarily alter the risk of stone formation, ie cause changes in calcium oxalate urine supersaturation, in patients with a history of nephrolithiasis.

Changes in Urinary Stone Risk Factors in Hypocitraturic Calcium Oxalate Stone Formers Treated With Dietary Sodium Supplementation

We investigated the effects of supplemental dietary sodium on risk factors for urinary stone disease in stone forming patients with hypocitraturia. Ten patients diagnosed with recurrent isolated hypocitraturic calcium urolithiasis were identified. Baseline 24-hour urinalysis was performed with patients on their regular diet, including citrate replacement with 20 mEq potassium citrate 3 times per day. Strict daily dietary logs were kept for a 7-day period, during which patients had normal oral intake and potassium citrate replacement. Patients then received supplemental sodium chloride for 1 week (1 gm orally 3 times per day), in addition to their regular diets and potassium citrate supplementation. Dietary logs were continued and 24-hour urinalysis was performed at the end of 1 week of supplemental sodium. Risk factors for urinary stone disease were compared using the Student t test and ANOVA. Two patients were unable to comply with sodium supplementation based on 24-hour urinalysis and, therefore, they were excluded from study. The remaining 8 patients were analyzed. Patients on supplemental dietary sodium demonstrated significantly increased mean urinary voided volume (933 ml per day above baseline, p <0.05) and mean urinary sodium excretion (66 mEq per day above baseline, p <0.05). There was no statistically significant change in urinary calcium, oxalate or uric acid. The urinary supersaturation relative risk ratio decreased for calcium oxalate stones (0.93 vs 0.63, p <0.05), while those of brushite, struvite and uric acid were not different before vs after supplemental sodium. Dietary sodium supplementation resulted in an increased voided urine volume and decreased the relative risk supersaturation ratio for calcium oxalate stones in patients with a history of hypocitraturic calcium oxalate nephrolithiasis. Urinary calcium excretion as well as other urine parameters that are risk factors for nephrolithiasis was not changed. Sodium restriction may be inappropriate in patients with hypocitraturia and recurrent urinary stones. Sodium supplementation may be beneficial in these patients because it results in voluntary increased fluid intake.

Fructose intake as a risk factor for kidney stone disease

Taylor and Curhan report that consumption of fructose is independently associated with an increased risk of incident kidney stones. What could be the mechanisms underlying the relation between fructose intake and stone risk? And how should we incorporate this finding into the dietary advice that we give to our patients to prevent kidney stone formation?

Fructose consumption and the risk of kidney stones

Fructose consumption has markedly increased over the past decades. This intake may increase the urinary excretion of calcium, oxalate, uric acid, and other factors associated with kidney stone risk. We prospectively examined the relationship between fructose intake and incident kidney stones in the Nurses' Health Study I (NHS I) (93,730 older women), the Nurses' Health Study II (NHS II) (101,824 younger women), and the Health Professionals Follow-up Study (45,984 men). Food frequency questionnaires were used to assess free fructose and sucrose intake every 4 years. Total-fructose intake was calculated as free fructose plus half the intake of sucrose, and expressed as percentage of total energy. Cox proportional hazard regressions were adjusted for age, body mass index (BMI), thiazide use, caloric intake, and other dietary factors. We documented 4902 incident kidney stones during a combined 48 years of follow-up. The multivariate relative risks of kidney stones significantly increased for participants in the highest compared to the lowest quintile of total-fructose intake for all three study groups. Free-fructose intake was also associated with increased risk. Non-fructose carbohydrates were not associated with increased risk in any cohort. Our study suggests that fructose intake is independently associated with an increased risk of incident kidney stones.

Urolithiasis in Pediatric Patients: A Single Center Study of Incidence, Clinical Presentation and Outcome

The incidence of kidney stones in adults has increased in the last 30 years. This retrospective, single site review was done to test the hypotheses that the incidence of urolithiasis in pediatric patients increased from 1994 to 2005, and that metabolic abnormalities were more common in patients with renal stones in the final 3 years of the study period. Charts from 2 time periods were reviewed, 1994 to 1996 (period 1) and 2003 to 2005 (period 2). Clinical and laboratory data, including demographics, presenting complaints, laboratory assessment, treatment and outcome, were tabulated in patients with confirmed urolithiasis. The number of patients with urolithiasis increased from 7 in period 1 to 61 in period 2. When expressed as cases per 100 new patients the incidence increased 4.6 times (p = 0.014). Focusing on period 2, 28% of patients were younger than 10 years. While blood tests were generally normal, 76% of patients had at least 1 abnormality in the 24-hour urine collection. Hypocitraturia, which was the most common metabolic abnormality, was noted in 52% of patients. The small number of patients in period 1 precluded determination as to whether metabolic abnormalities were more common in period 2. Surgery and/or lithotripsy was required in 12 children. Stone disease recurred in 39% of the patients. The incidence of urolithiasis in the pediatric population increased nearly 5-fold at our institution during the last decade. We recommend that the primary diagnostic test be a 24-hour urine collection. The most common metabolic abnormality was hypocitraturia, followed by hypercalciuria. Recurrence of stones is common (approximately 40% rate) and followup is advised.

Dietary Factors and the Risk of Incident Kidney Stones in Younger Women. Nurses’ Health Study II

No AccessJournal of UrologyUrological Survey: Urolithiasis, Endourology and Laparoscopy1 Feb 2005Dietary Factors and the Risk of Incident Kidney Stones in Younger Women. Nurses’ Health Study II Ralph V. ClaymanM.D. Ralph V. ClaymanRalph V. Clayman More articles by this author View All Author Informationhttps://doi.org/10.1016/S0022-5347(05)60511-3AboutFull TextPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail "Dietary Factors and the Risk of Incident Kidney Stones in Younger Women. Nurses’ Health Study II." The Journal of Urology, 173(2), p. 479 © 2005FiguresReferencesRelatedDetails Volume 173Issue 2February 2005Page: 479 Advertisement Copyright & Permissions© 2005MetricsAuthor Information Ralph V. Clayman More articles by this author Expand All Advertisement PDF downloadLoading ...

Dietary Factors and the Risk of Incident Kidney Stones in Men

Diet plays an important role in the pathogenesis of kidney stones. Because the metabolism of many dietary factors, such as calcium, may change with age, the relation between diet and kidney stones may be different in older adults. Uncertainty also remains about the association between many dietary factors, such as vitamin C, magnesium, and animal protein, and the risk of kidney stone formation. To examine the association between dietary factors and the risk of incident, symptomatic kidney stones in men and to determine whether these associations vary with age, a prospective cohort study was conducted of 45,619 men without a history of nephrolithiasis. Self-administered food frequency questionnaires were used to assess diet every 4 yr. A total of 1473 incident symptomatic kidney stones were documented during 477,700 person-years of follow-up. For men aged <60 yr, the multivariate relative risk (RR) for stone formation in the highest quintile of dietary calcium as compared with the lowest quintile was 0.69 (95% confidence interval [CI], 0.56 to 0.87; P = 0.01 for trend). By contrast, there was no association between dietary calcium and stone formation in men aged 60 yr or older. The multivariate RR for men who consumed 1000 mg or greater of vitamin C per day compared with those who consumed less than the recommended dietary allowance of 90 mg/d was 1.41 (95% CI, 1.11 to 1.80; P = 0.01 for trend). Other dietary factors showed the following multivariate RR among men in the highest quintile of intake compared with those in the lowest: magnesium, 0.71 (95% CI, 0.56 to 0.89; P = 0.01 for trend); potassium, 0.54 (95% CI, 0.42 to 0.68; P < 0.001 for trend); and fluid, 0.71 (95% CI, 0.59 to 0.85; P < 0.001 for trend). Animal protein was associated with risk only in men with a body mass index <25 kg/m(2) (RR, 1.38; 95% CI, 1.05 to 1.81; P = 0.03 for trend). Sodium, phosphorus, sucrose, phytate, vitamin B(6), vitamin D, and supplemental calcium were not independently associated with risk. In conclusion, the association between calcium intake and kidney stone formation varies with age. Magnesium intake decreases and total vitamin C intake seems to increase the risk of symptomatic nephrolithiasis. Because age and body size affect the relation between diet and kidney stones, dietary recommendations for stone prevention should be tailored to the individual patient.

Dietary factors and the risk of incident kidney stones in younger women: Nurses' Health Study II.

In older women and men, greater intakes of dietary calcium, potassium, and total fluid reduce the risk of kidney stone formation, while supplemental calcium, sodium, animal protein, and sucrose may increase the risk. Recently, phytate has been suggested to play a role in stone formation. To our knowledge, no prospective information on the role of dietary factors and risk of kidney stone formation is available in younger women. We prospectively examined, during an 8-year period, the association between dietary factors and the risk of incident symptomatic kidney stones among 96 245 female participants in the Nurses' Health Study II; the participants were aged 27 to 44 years and had no history of kidney stones. Self-administered food frequency questionnaires were used to assess diet in 1991 and 1995. The main outcome measure was an incident symptomatic kidney stone. Cox proportional hazards regression models were used to adjust simultaneously for various risk factors. We documented 1223 incident symptomatic kidney stones during 685 973 person-years of follow-up. After adjusting for relevant risk factors, a higher dietary calcium intake was associated with a reduced risk of kidney stones (P =.007 for trend). The multivariate relative risk among women in the highest quintile of intake of dietary calcium compared with women in the lowest quintile was 0.73 (95% confidence interval, 0.59-0.90). Supplemental calcium intake was not associated with risk of stone formation. Phytate intake was associated with a reduced risk of stone formation. Compared with women in the lowest quintile of phytate intake, the relative risk for those in the highest quintile was 0.63 (95% confidence interval, 0.51-0.78). Other dietary factors showed the following relative risks (95% confidence intervals) among women in the highest quintile of intake compared with those in the lowest quintile: animal protein, 0.84 (0.68-1.04); fluid, 0.68 (0.56-0.83); and sucrose, 1.31 (1.07-1.60). The intakes of sodium, potassium, and magnesium were not independently associated with risk after adjusting for other dietary factors. A higher intake of dietary calcium decreases the risk of kidney stone formation in younger women, but supplemental calcium is not associated with risk. This study also suggests that some dietary risk factors may differ by age and sex. Finally, dietary phytate may be a new, important, and safe addition to our options for stone prevention.

The association between gout and nephrolithiasis in men: The Health Professionals' Follow-Up Study

Approximately 10 million adults in the United States have experienced the passage of a kidney stone, and up to 5 million have been diagnosed with gout by a physician. Previous reports have suggested that gout increases the risk for the development of kidney stones, but there are no prospective data. We used data from a cohort of 51,529 male health care professionals to examine the independent association between gout and kidney stone disease. In a cross-sectional analysis of gout and kidney stone disease reported on the 1986 baseline questionnaire, the prevalence of kidney stone disease was almost twofold higher in men with history of gout compared to those without (15% vs. 8%). After adjusting for age and body mass index (BMI), a history of gout remained significantly associated with kidney stone disease (OR 1.88; 95% CI 1.68 to 2.11). We then prospectively examined the risk of incident kidney stones in men with and without a confirmed diagnosis of gout after excluding men who reported a history of kidney stone disease or gout on the baseline questionnaire. A confirmed diagnosis of gout increased the multivariate relative risk of incident kidney stones (RR 2.12; 95% CI 1.22 to 3.68). In contrast, a history of kidney stone disease was not associated with increased risk of gout (RR 1.05; 95% CI 0.54 to 2.07). In conclusion, a history of gout independently increases the risk for incident kidney stones in men. Physicians should provide dietary counseling, such as increasing fluid intake and decreasing salt consumption, to subjects with gout in addition to other risk factors, such as family history of kidney stones, in order to decrease the likelihood of stone formation.

Menopause and postmenopausal hormone use and risk of incident kidney stones.

Menopause is associated with increased urinary calcium excretion, which could increase the risk for the development of calcium-containing kidney stones. However, it is unknown whether menopause and postmenopausal hormone (PMH) use are independent risk factors for incident kidney stone disease in women. Data from 91,731 female Nurses' Health Study participants who provided information on diet, menopause status, and kidney stone disease were used to examine the independent association between menopause and PMH use and risk of incident kidney stones. No association was found between menopause and incident kidney stones in age-adjusted (relative risk [RR], 1.07; 95% CI, 0.85 to 1.34) or multivariate models (RR, 1.12; 95% CI, 0.89 to 1.41). However, when the association between the type of menopause and risk of incident kidney stones was examined, surgical menopause was associated with an increased risk in both the age-adjusted (RR, 1.37; 95% CI, 1.05 to 1.77) and multivariate models (RR, 1.39; 95% CI, 1.07 to 1.81), whereas natural menopause was not. Compared with never-use, past or current PMH use (including duration of PMH use) was not associated with incident kidney stones among postmenopausal women. In conclusion, no association was found between menopause and PMH use and incident kidney stones. Surgical menopause, however, may be associated with an increased risk.