Seasonal variations in urinary calcium, volume, and vitamin D in kidney stone formers

ABSTRACT Objectives: To investigate the seasonal variations in urinary calcium, serum vitamin D, and urinary volume in patients with a history of nephrolithiasis. Materials and Methods: Patients included were those who completed a 24-hour urine metabolic evaluation on two occasions; one in summer (June-Aug) and one in winter (Nov-Jan), and who had not started any medications or been instructed on dietary modifications in the interval between the two tests that may have impacted the results. Patients were excluded if they were on thiazide diuretics or were taking calcium and / or Vitamin D supplementation. Welch's t-test was used to compare the difference in average summer and winter values. Unpaired Student t-test was used to compare baseline parameters (age, BMI), and Paired Student t-test was used to compare average seasonal measurements in men vs. women. Results: 136 patients were identified who were not taking calcium or vitamin D supplements or thiazide diuretics, and who were not instructed on dietary modifications in the interval between the two measured parameters. No significant differences were observed when comparing male to female baseline parameters of age or BMI (Table-1). Average 24-hour urine calcium was higher (226.60) in the winter than in summer (194.18) and was significant in males (p = 0.014) and females (p < 0.001). No significant seasonal difference was seen in 24-hour urine volume or serum vitamin D levels. Conclusions: Urinary calcium is higher in winter months compared to summer months. As such, tailoring medical preventative strategies to the time of year may be helpful.

Seasonal variations in urinary calcium, volume, and vitamin d in kidney stone formers.

OBJECTIVES: To investigate the seasonal variations in urinary calcium, serum vitamin D, and urinary volume in patients with a history of nephrolithiasis. MATERIALS AND METHODS: Patients included were those who completed a 24-hour urine metabolic evaluation on two occasions; one in summer (June-Aug) and one in winter (Nov-Jan), and who had not started any medications or been instructed on dietary modifications in the interval between the two tests that may have impacted the results. Patients were excluded if they were on thiazide diuretics or were taking calcium and / or Vitamin D supplementation. Welch's t-test was used to compare the difference in average summer and winter values. Unpaired Student t-test was used to compare baseline parameters (age, BMI), and Paired Student t-test was used to compare average seasonal measurements in men vs. women. RESULTS: 136 patients were identified who were not taking calcium or vitamin D supplements or thiazide diuretics, and who were not instructed on dietary modifications in the interval between the two measured parameters. No significant differences were observed when comparing male to female baseline parameters of age or BMI (Table-1). Average 24-hour urine calcium was higher (226.60) in the winter than in summer (194.18) and was significant in males (p = 0.014) and females (p < 0.001). No significant seasonal difference was seen in 24-hour urine volume or serum vitamin D levels. CONCLUSIONS: Urinary calcium is higher in winter months compared to summer months. As such, tailoring medical preventative strategies to the time of year may be helpful.

Can obese stone formers follow dietary recommendations?

INTRODUCTION: Obese patients have an increased risk of kidney stones, and several studies have identified specific urinary derangements on 24-hour collections. The objective of this study was to assess obese and super-obese stone formers, and their compliance with dietary modifications over time, based on 24-hour urine outcomes. PATIENTS AND METHODS: A retrospective review was performed searching for all stone formers who completed a 24-hour urine collection before and after dietary counseling for stone prevention. Patients were excluded if placed on medical therapy in addition to dietary therapy. Patients were divided in three main groups according to their body mass index (BMI): 30, 30-40, and >40 kg/m(2). Demographic data and 24-hour urine stone risk parameters (volume, sodium, uric acid, citrate, and oxalate) were assessed. Initial 24-hour urine results were compared to follow-up results after dietary counseling. Then, the outcomes from each group were compared to each other. RESULTS: Two hundred and fourteen stone formers (67% male) were identified with a mean age of 49.5±15.0 years. One hundred twenty-eight (59.8%) patients had BMI <30 kg/m(2), 61 (28.5%) between 30-40 kg/m(2), and 25 (11.7%) >40 kg/m(2). Among patients with BMI <30 kg/m(2), there were significant improvements in all urinary parameters (p<0.001) as well as in the group with BMI between 30 to 40 kg/m(2) (p=0.02 for oxalate, p<0.001 for other parameters). Among super-obese patients, there were significant improvements in the urinary volume (p=0.03), sodium (p<0.001), uric acid (p=0.001), and oxalate (p<0.001). There were no significant differences in the improvements observed in the urinary volume (p=0.69), sodium (p=0.08), uric acid (p=0.17), and citrate levels (p=0.97) between the groups. CONCLUSION: Dietary recommendations can be an equally effective strategy in decreasing the risk or stone recurrence in obese and super-obese kidney stone formers as it is in those who are not obese.