***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND We have previously reported that in the Olivetti Prospect i ve Heart Study cohort the incidence of nephrolithiasis was higher in hypertensive participants than in normotensive ones . As the time sequence and the mechanisms underlying the association between nephrolithiasis and hypertension remain controversial , we further tested the hypothesis that in a cohort of normotensive males a history of nephrolithiasis predicts the development of future hypertension . METHODS The analysis was conducted in 381 male workers at Olivetti who were normotensive at the baseline examination and who were re-examined 8 years later . RESULTS A past history of nephrolithiasis is associated with an increased risk of hypertension of 1.96 ( 95 % CI=1.25 - 3.07 ) relative to subjects with a negative history , after adjusting for age . CONCLUSION In this 8-year follow-up study , a history of nephrolithiasis result ed in an increased risk of developing hypertension in the future . As the reverse was also true , as previously reported , a clear-cut time sequence , as well as the mechanisms linking these two conditions , remain to be identified BACKGROUND Insulin resistance is a central feature of type 2 diabetes mellitus ( DM ) and may increase the risk of kidney stone formation . Existing cross-sectional data on the association between DM and nephrolithiasis are limited , and no prospect i ve study to date has evaluated the relation between DM and the risk of kidney stones . METHODS To evaluate the relation between DM and prevalent kidney stones , we conducted a cross-sectional study of 3 large cohorts including over 200,000 participants : the Nurses ' Health Study I ( older women ) , the Nurses ' Health Study II ( younger women ) , and the Health Professionals Follow-up Study ( men ) . We then prospect ively studied the association between DM and incident nephrolithiasis over a combined 44 years of follow-up . Because insulin resistance can precede the diagnosis of DM by decades , we also prospect ively examined the relation between kidney stones and the diagnosis of incident DM . Multivariate regression models adjusted for age , body mass index , thiazide diuretic use , fluid intake , and dietary factors . RESULTS At baseline , the multivariate relative risk of prevalent stone disease in individuals with DM compared to individuals without was 1.38 ( 95 % CI 1.06 - 1.79 ) in older women , 1.67 ( 95 % CI 1.28 - 2.20 ) in younger women , and 1.31 ( 95 % CI 1.11 - 1.54 ) in men . Prospect ively , the multivariate relative risk of incident kidney stone formation in participants with DM compared to participants without was 1.29 ( 95 % CI 1.05 - 1.58 ) in older women , 1.60 ( 95 % CI 1.16 - 2.21 ) in younger women , and 0.81 ( 95 % CI 0.59 - 1.09 ) in men . The multivariate relative risk of incident DM in participants with a history of kidney stones compared to participants without was 1.33 ( 95 % CI 1.18 - 1.50 ) in older women , 1.48 ( 95 % CI 1.14 - 1.91 ) in younger women , and 1.49 ( 95 % CI 1.29 - 1.72 ) in men . CONCLUSION DM is a risk factor for the development of kidney stones . Additional studies are needed to determine if the increased risk of DM in stone formers is due to sub clinical insulin resistance BACKGROUND 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 prospect i ve information on the role of dietary factors and risk of kidney stone formation is available in younger women . METHODS We prospect ively 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 question naires 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 . RESULTS 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 . CONCLUSIONS 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 Dietary factors are believed to play an important role in the formation of kidney stones [ 1 , 2 ] , but data on the influence of diet on stone formation in women are limited . The incidence of kidney stones in women is one third the incidence in men [ 3 ] ; the reason for this marked difference is unknown . Although differences in diet may contribute , the only available data on which comparisons between men and women can be based are from casecontrol studies that included few women . No studies have provided prospect i ve data on the relation between diet and kidney stones in women . In the past , a diet high in calcium was suspected of increasing the risk for calcium-containing kidney stones , particularly stones consisting of calcium oxalate ( the most common type ) . This finding has often led to restriction of calcium intake in patients who have had kidney stones in an attempt to decrease the likelihood of recurrence . In a large prospect i ve study in men , however , we recently found that high intake of dietary calcium was associated with a decreased risk for stone formation [ 2 ] . One possible explanation of this observation is that high calcium intake reduces oxalate absorption and subsequent urinary excretion of oxalate by binding oxalate in the gastrointestinal tract . Urinary oxalate may be more important than urinary calcium with respect to formation of calcium oxalate crystals [ 4 ] . Moreover , restriction of dietary calcium intake may result in negative calcium balance and decreased bone mineral density , particularly in patients with idiopathic hypercalciuria [ 5 ] . Supplemental calcium , such as calcium carbonate , is commonly used by adults in the United States . Large doses have been recommended for the prevention of various common disorders in women , such as osteoporosis and preeclampsia [ 6 , 7 ] . Although some research ers are concerned that high doses of supplemental calcium may increase the risk for kidney stone formation [ 7 ] , no data are available on this issue in women . Use of supplemental calcium increases urinary calcium excretion ; if not taken with meals , these supplements do not decrease urinary oxalate excretion . Thus , the overall effect of supplemental calcium may actually be an increased risk for stone formation . Clearly , information on the risk for stone formation associated with intake of supplemental calcium is essential to help patients decide whether to begin or continue to use calcium supplements . Other dietary factors may also be associated with the risk for kidney stone formation [ 1 , 2 ] . A diet high in sodium [ 8 ] , sucrose [ 9 ] , or animal protein [ 10 ] may increase the risk for stone formation , whereas a diet high in potassium [ 11 ] , magnesium [ 12 ] , or fluid may decrease this risk . To study the association between intake of dietary and supplemental calcium and other nutrients and the incidence of kidney stones in women , we conducted a 12-year prospect i ve analysis among 91 731 women who were participating in the Nurses ' Health Study and had no history of kidney stones at study entry . Methods Study Sample In 1976 , 121 700 female registered nurses who were 30 to 55 years of age and resided in 1 of 11 U.S. states completed and returned the initial question naire . These women constitute the Nurses ' Health Study cohort [ 13 ] . The cohort is followed by using biennial mailed question naires that ask about lifestyle practice s and other exposures of interest , as well as the incidence of newly diagnosed disease . The sample for our analysis was limited to the 91 731 women who answered the 1992 question naire , which included a question on lifetime history of kidney stones , and who had completed at least one of the four dietary question naires since 1980 ( the first year in which information on diet was collected ) .  Assessment of Diet In 1980 , 1984 , 1986 , and 1990 , the participants were asked to complete semiquantitative food-frequency question naires , on which they reported the average intake of specified foods and beverages during the past year . The 1980 dietary question naire contained 61 items , and the subsequent question naires contained 131 items . Nutrient intake was computed from the reported frequency of consumption of each specified unit of food or beverage and from published data on the nutrient content of the specified portions [ 14 ] . Beginning in 1984 , information was also collected on the amount of supplemental calcium ( such as calcium carbonate ) ingested , either as separate supplements or as part of multivitamin preparations . The reproducibility and validity of the question naires completed by women in this cohort have been documented elsewhere [ 14 ] . A similar question naire has been shown to be valid and reproducible in men [ 15 ] . Nutrient values were adjusted for total energy intake by regressing total caloric intake on absolute nutrient intake [ 16 , 17 ] . Because total energy intake for a given person tends to be fixed within a narrow range , variations in nutrient intake are largely attributable to changes in composition of diet , not the total amount of food consumed . Energy-adjusted values reflect the nutrient composition of the diet independent of the total amount of food consumed . In addition , adjustment for energy reduces any variation introduced by question naire responses that underreported or overreported intake , thereby improving the accuracy of nutrient measurements [ 16 , 17 ] . To obtain additional information on the typical pattern of the use of supplemental calcium , we mailed a question naire to a r and om sample of 100 women who reported taking supplemental calcium on the 1994 biennial question naire . Eighty-six of these women responded . The question naire asked about the specific type of calcium salt ingested and whether the supplement was taken alone or with particular meals . Follow-up and Ascertainment of Cases The 1992 question naire asked whether the woman had ever received a diagnosis of a kidney stone and , if so , the date of the first occurrence . If the participant reported that a kidney stone had been diagnosed in 1980 ( when dietary information was first collected ) or later , we mailed her a supplementary question naire to confirm the diagnosis and to ascertain the date of occurrence ; the type of symptoms ; other relevant medical conditions ; and , if known , the type of stone . The rate of response to this supplementary question naire was 95 % . To confirm the validity of the participants ' reports , we obtained the medical records from a r and om sample of 90 of the women who reported a kidney stone . The records confirmed the diagnosis for all but 1 woman . We considered only cases of kidney stones that were diagnosed during the 12 years between the date on which the 1980 question naire was returned and 31 May 1992 . After we excluded women for whom the date of the kidney stone either could not be confirmed or fell outside of the study period , 91 731 women with no history of kidney stones remained in the study group . Statistical Analysis The study design was prospect i ve , and information on diet was collected before the onset of the kidney stone . For each participant , person-months of follow-up were counted from the date on which the 1980 question naire was returned 1 ) to the date on which a kidney stone developed or death occurred or 2 ) to 31 May 1992 , whichever occurred first . Information on exposures of interest that were recorded in responses to the 1980 question naire was up date d in 1984 , 1986 , and 1990 . We allocated person-months of follow-up according to exposure status at the start of each follow-up period ( indicated by the quintile of 
    Output:
    
Patients with metabolic syndrome have an increased risk of having urolithiasis indicating that it should be assessed as a systemic disorder .