Relationship between serum vitamin D and 24-hour urine calcium in patients with nephrolithiasis

Sleep and circadian rhythm disturbance in kidney stone disease: a narrative review

The circadian rhythm generated by circadian clock genes functions as an internal timing system. Since the circadian rhythm controls abundant physiological processes, the circadian rhythm evolved in organisms is salient for adaptation to environmental change. A disturbed circadian rhythm is a trigger for numerous pathological events. Recently, accumulated data have indicated that kidney stone disease (KSD) is related to circadian rhythm disturbance. However, the mechanism between them has not been fully elucidated. In this narrative review, we summarized existing evidence to illustrate the possible association between circadian rhythm disturbance and KSD based on the epidemiological studies and risk factors that are linked to circadian rhythm disturbance and discuss some chronotherapies for KSD. In summary, KSD is associated with systemic disorders. Metabolic syndrome, inflammatory bowel disease, and microbiome dysbiosis are the major risk factors supported by sufficient data to cause KSD in patients with circadian rhythm disturbance, while others including hypertension, vitamin D deficiency, parathyroid gland dysfunction, and renal tubular damage/dysfunction need further investigation. Then, some chronotherapies for KSD were confirmed to be effective, but the molecular mechanism is still unclear.

A path analysis to investigate the interaction between serum, urinary and demographic factors influencing urine calcium in kidney stone formers

BACKGROUND

Hypercalciuria is one of the most important urinary risk factors in kidney stone formers. This study aimed to delineate the interaction of some demographic, serum, and urinary risk factors influencing 24-h urinary (24-U) calcium excretion.

METHODS

This study was secondary data analysis, using data from 593 kidney stone patients referred to the Labbafinejad kidney stone prevention clinic from March 2015 to May 2019. The study considered serum, urinary and demographic factors that interact to influence 24-U calcium using path analysis. In addition to the direct impact of predictors on the 24-U calcium, this analysis considered the effects of the predictors on the 24-U calcium transmitted by a mediating variable named indirect effects.

RESULTS

The results showed that age indirectly affected on 24-U calcium through 25-hydroxy vitamin D (25(OH)D), serum and 24-U creatinine. As well, weight had an indirect effect through 24-urine metabolites (creatinine, citrate, urea, and sodium). Among serum variables, PTH and creatinine significantly directly affected on 24-U calcium. In comparison, 25(OH)D and phosphorus appeared to influence 24-U calcium indirectly through serum parathormone. Regarding 24-U metabolites, sodium, urea, and citrate had a significant direct effect on 24-U calcium. Moreover, 24-U creatinine has a significant direct and indirect effect on 24-U calcium through citrate and urea as mediator variables.

CONCLUSION

Serum 25(OH)D and phosphorus, along with age and weight, indirectly affected urinary calcium through a third variable. Other variables (PTH, serum creatinine, and 24-U sodium, urea, and citrate) showed a direct effect on 24-U calcium excretion.

Beta-thalassaemia major: Prevalence, risk factors and clinical consequences of hypercalciuria

Regular transfusion and chelation therapy produces increased life expectancy in thalassaemic patients who may develop new complications. Since few data are available regarding hypercalciuria in β‐thalassaemia major (TM), the aim of our study was to evaluate its prevalence, risk factors and clinical consequences. We enrolled 176 adult TM patients followed at the Center of Thalassemia of Ferrara. Hypercalciuria was defined by a calciuria of 4 mg/kg/day or more in a 24‐h urine sample. Anamnestic, biochemical and radiological data were collected. Hypercalciuria prevalence was reported in 69.3% of patients (females 52.5%). Hypercalciuric (HC) patients used deferasirox (DFX) more often than normocalciuric (NC) patients (47.5% vs 29.6%; p < 0.05). In HC subjects plasma parathyroid hormone (PTH) (24.1 ± 10.4 vs 30.1 ± 13.2 pg/ml) and phosphate levels (3.6 ± 0.5 vs 3.8 ± 0.7 mg/dl) were lower, whereas serum calcium (9.6 ± 0.4 vs 9.4 ± 0.4 mg/dl) and urinary 24‐h phosphaturia (0.9 ± 0.4 vs 0.6 ± 0.3 g/day) were higher as compared to NC patients (p < 0.05 for all comparisons). Supplementation with oral calcium and cholecalciferol was similar between the groups. A higher rate of kidney stones was present in HC (14.8%) versus NC patients (3.7%) (p < 0.05). Hypercalciuria is a frequent complication in adequately treated adult TM patients. Hypercalciuria prevalence is increased in DFX users whereas haemoglobin level or calcium supplements play no role. A significant proportion of HC patients developed kidney stones.

Effect of Vitamin D Treatment on Dynamics of Stones Formation in the Urinary Tract and Bone Density in Children with Idiopathic Hypercalciuria

Vitamin D supplementation in patients with urolithiasis and hypercalciuria is considered to be unsafe. We analyzed the impact of vitamin D supplementation on selected health status parameters in children with idiopathic hypercalciuria. The study included 36 children with urolithiasis resulting from excessive calcium excretion. The level of calcium and 25(OH)D (hydroxylated vitamin D - calcidiol) in serum, urinary calcium excretion and the presence of stones in urinary tract were assessed prospectively. Blood and urine samples were collected at the time when the patient was qualified for the study and every three months up to 24 month of vitamin D intake at a dose of 400 or 800 IU/day. At time zero and at 12, and 24 months of vitamin D supplementation, densitometry was performed. Supplementation with vitamin D caused a statistically significant increase in the concentration of 25(OH)D in serum. There were no significant changes in calcium concentration in serum, excretion of calcium in urine but also in bone density. There was no significant increase in the risk of formation or development of stones in the urinary tract. Supplementation with vitamin D (400–800 IU/day) in children with idiopathic hypercalciuria significantly increases 25(OH)D concentration, does not affect calciuria, but also does not improve bone density.

Metabolic effects of cholecalciferol supplementation in patients with calcium nephrolithiasis and vitamin D deficiency

INTRODUCTION

In this paper, we investigated whether cholecalciferol supplementation may increase the risk of stone recurrence in patients with calcium nephrolithiasis and Vitamin D deficiency.

METHODS

Thirty-three stone formers (56 ± 17 years old, 12 males) with 25(OH)D < 20 ng/mL were considered. Calcium excretion and urine supersaturation with calcium oxalate (ßCaOx) and brushite (ßbsh) were evaluated, both before and after cholecalciferol supplementation. Values of ß > 1 mean supersaturation. Cholecalciferol was prescribed as oral bolus of 100,000-200,000 IU, followed by weekly (5000-10,000 IU) or monthly (25,000-50,000 IU) doses. Calcium intake varied between 800 and 1000 mg/day. In urine, total nitrogen (TNE) was taken as an index of protein intake, sodium as a marker of dietary intake, and net acid excretion (NAE) as an index of acid-base balance.

RESULTS

TNE, sodium, and NAE did not change during the study (p = ns). Compared to baseline values, after cholecalciferol, both serum calcium and phosphate did not vary (p = ns); 25(OH)D increased from 11.8 ± 5.5 to 40.2 ± 12.2 ng/mL (p < 0.01); 1.25(OH)₂D increased from 41.6 ± 17.6 to 54 ± 16 pg/mL (p < 0.01); PTH decreased from 75 ± 27.2 to 56.7 ± 21.1 pg/mL (p < 0.01); urinary calcium increased from 2.7 ± 1.5 to 3.6 ± 1.6 mg/Kg b.w. (p < 0.01); ßbsh increased from 0.9 ± 0.7 to 1.3 ± 1.3 (p = 0.02); whereas ßCaOx varied but not significantly. Before cholecalciferol supplementation, 6/33 patients were hypercalciuric (i.e., urine Ca ≥ 4 mg/Kg b.w.) and increased to 13/33 after cholecalciferol supplementation (pX² = 0.03).

CONCLUSIONS

Cholecalciferol supplementation may increase calcium excretion, or reveal an underlying condition of absorptive hypercalciuria. This may increase both urine supersaturation with calcium salts and stone-forming risk.

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.

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.

Vitamin D, Hypercalciuria and Kidney Stones

The estimated lifetime risk of nephrolithiasis is growing nowadays, and the formation of kidney stones is frequently promoted by hypercalciuria. Vitamin D, and especially its active metabolite calcitriol, increase digestive calcium absorption—as urinary calcium excretion is directly correlated with digestive calcium absorption, vitamin D metabolites could theoretically increase calciuria and promote urinary stone formation. Nevertheless, there was, until recently, low evidence that 25-hydroxyvitamin D serum levels would be correlated with kidney stone formation, even if high calcitriol concentrations are frequently observed in hypercalciuric stone formers. Low 25-hydroxyvitamin D serum levels have been associated with a broad spectrum of diseases, leading to a huge increase in vitamin D prescription in the general population. In parallel, an increased frequency of kidney stone episodes has been observed in prospective studies evaluating vitamin D alone or in association with calcium supplements, and epidemiological studies have identified an association between high 25-hydroxyvitamin D serum levels and kidney stone formation in some groups of patients. Moreover, urinary calcium excretion has been shown to increase in response to vitamin D supplements, at least in some groups of kidney stone formers. It seems likely that predisposed individuals may develop hypercalciuria and kidney stones in response to vitamin D supplements.

Factors influencing pre-operative urinary calcium excretion in primary hyperparathyroidism

OBJECTIVE

Normal or elevated 24-hour urinary calcium (Ca) excretion is a diagnostic marker in primary hyperparathyroidism (PHPT). It is used to distinguish familial hypocalciuric hypercalcaemia (FHH) from PHPT by calculating the Ca/creatinine clearance ratio (CCCR). The variance of CCCR in patients with PHPT is considerable. The aim of this study was to analyse the parameters affecting CCCR in patients with PHPT.

DESIGN

The data were collected prospectively. Patients with sporadic PHPT undergoing successful surgery were included in a retrospective analysis.

PATIENTS

The analysis covered 381 patients with pre-operative workup 2 days before removal of a solitary parathyroid adenoma.

MEASUREMENTS

The impact of serum Ca and 25-hydroxyvitamin D3 (25-OH D3) on CCCR.

RESULTS

The coefficient of determination (R² ) in the multivariable model for CCCR consisting of age, Ca, 25-OH D3, 1,25-dihydroxyvitamin D3 (1,25-(OH)2 D3), testosterone (separately for males and females), intact parathyroid hormone (iPTH) and osteocalcin was 25.8%. The only significant parameters in the multivariable analysis were 1,25-(OH)2 D3 and osteocalcin with a drop in R² of 15.4% (P<.001) and 2.4% (P=.006), respectively. Bone mineral densities at the lumbar spine, distal radius and left femoral neck were not associated with CCCR (r=-.08, r=-.10 and r=-0.09).

CONCLUSIONS

In multivariable analysis, 1,25-(OH)2 D3 and osteocalcin were the only factors correlating with CCCR. Vitamin D3 replacement may therefore impair the diagnostic value of CCCR and increase the importance of close monitoring of urinary Ca excretion during treatment.

Increased risk of endotracheal intubation and heart failure following acute myocardial infarction in patients with urolithiasis: a nationwide population-based study

BACKGROUND

Urolithiasis is a common urinary tract disease worldwide. It has been connected to systemic diseases, including hypertension, diabetes mellitus, metabolic syndrome, and cardiovascular disease. In the current study, we aimed to evaluate the relationship between urolithiasis and the complications of acute myocardial infarction (AMI).

MATERIALS AND METHODS

Data were obtained from the Longitudinal Health Insurance Database 2005 of the National Health Insurance Research Database. All AMI cases, both those who were hospitalized and those who were treated in the emergency department, were identified using the International Classification of Diseases, ninth revision, Clinical Modification (ICD-9-CM) code.

RESULTS

A total of 37,052 patients with urinary calculi and 148,209 control subjects were enrolled in this study. The average follow-up period was 9.51 years. The risk of AMI was higher among patients with urolithiasis (adjusted hazard ratio [aHR] 1.07, 95% confidence interval [95% CI] 1.03-1.13). We detected a significant association between urolithiasis and intubation (aHR 1.53, 95% CI 1.36-1.73), intensive care unit treatment (aHR 1.22, 95% CI 1.13-1.32), heart failure (aHR 1.59, 95% CI 1.42-1.78), shock (aHR 1.53, 95% CI 1.32-1.77), and arrhythmias (aHR 1.18, 95% CI 1.06-1.33). Furthermore, certain medical treatments for urolithiasis were found to be related to myocardial infarction (MI). Nonsteroidal anti-inflammatory drugs (NSAIDs) were significantly associated with a high risk of AMI. In contrast, allopurinol, thiazide diuretic, potassium-sparing diuretics, and α-blockers have negative association with AMI.

CONCLUSION

Urolithiasis had a significantly increased risk of endotracheal intubation and heart failure following AMI. In addition, urolithiasis was also associated with a high risk of intensive care unit treatment, shock, and arrhythmias after AMI. Medical treatments for urolithiasis may decrease the risk of MI, except the use of NSAIDs.

Epidemiology of stone disease across the world

Nephrolithiasis is a highly prevalent disease worldwide with rates ranging from 7 to 13% in North America, 5-9% in Europe, and 1-5% in Asia. Due to high rates of new and recurrent stones, management of stones is expensive and the disease has a high level of acute and chronic morbidity. The goal of this study is to review the epidemiology of stone disease in order to improve patient care. A review of the literature was conducted through a search on Pubmed^®, Medline^®, and Google Scholar^®. This review was presented and peer-reviewed at the 3rd International Consultation on Stone Disease during the 2014 Société Internationale d'Urologie Congress in Glasgow. It represents an update of the 2008 consensus document based on expert opinion of the most relevant studies. There has been a rising incidence in stone disease throughout the world with a narrowing of the gender gap. Increased stone prevalence has been attributed to population growth and increases in obesity and diabetes. General dietary recommendations of increased fluid, decreased salt, and moderate intake of protein have not changed. However, specific recommended values have either changed or are more frequently reported. Geography and environment influenced the likelihood of stone disease and more information is needed regarding stone disease in a large portion of the world including Asia and Africa. Randomized controlled studies are lacking but are necessary to improve recommendations regarding diet and fluid intake. Understanding the impact of associated conditions that are rapidly increasing will improve the prevention of stone disease.

Vitamin D deficiency/insufficiency from childhood to adulthood: Insights from a sunny country

Vitamin D is known to be a key regulator of bone metabolism and is associated with muscle strength. Vitamin D deficiency is widely prevalent worldwide. In adults, vitamin D deficiency has been implicated in numerous health conditions including osteoporosis, cancer, diabetes, and autoimmune diseases. Considerable changes have occurred in lifestyles and childhood activities in the past years. Studies have shown that the children population is at high risks of vitamin D deficiency. The objective of this study was to learn about the extent of vitamin D deficiency in children worldwide and especially in sunny country like Israel. In this article we reviewed the extent and severity of vitamin D deficiency worldwide and especially in Israel, through a very comprehensive review of previous reports and research studies done during the last years. We found reports on vitamin D deficiency in children, which was associated with metabolic syndromes and obesity. It was more prevalent in children who spend less time on outdoor activities, in obese children, and in cases when there was imbalance between nutritional intakes and requirements. Vitamin D deficiency is common even in children living in sunny places like Israel. Health professionals should be aware of the fact that although vitamin D deficiency is prevalent in the elderly population, it is also common in children, and can be associated with different illnesses. We encourage supplementation of vitamin D to special populations (pregnant and lactating women, infants, and high risk groups). We also encourage implementation of international food fortification programs.

Analysis of vitamin D deficiency in calcium stone-forming patients

PURPOSE

The aim of this study is to analyse the percentage of hypovitaminosis D, as well as its relationship with the various parameters of calcium-phosphate metabolism.

METHODS

A case control study was conducted on 366 patients, divided into two groups: Group 1: 127 non-stone-forming patients, and Group 2: 239 calcium stone forming. A study was performed on calcium-phosphate metabolism and urinary lithogenic factors. The percentage of vitamin D deficiency (25-OH-vitamin D levels <20 ng/ml) between the groups was analysed and compared. The SPSS 20.0 statistics program was used for the analysis, with a p ≤ .05 being considered significant.

RESULTS

The mean age of Group 1 was 52.1 years compared to 49.6 years in Group 2, with no significant differences (p = .07). Vitamin D levels were lower in Group 2 compared to Group 1 (25.7 vs. 28.4 ng/ml, p = .02). A vitamin D deficiency was observed in 28 % of the Group 2 stone-forming patients versus 15.7 % in Group 1 (p = .009), with an odds ratio (OR) of 2.09 (95 % CI; 1.19-3.63). In the stone-forming patients with a vitamin D deficiency, the only difference observed was the higher levels of iPTH compared to those stone-formers with a normal vitamin D (56.9 vs. 45.5 pg/ml, respectively; p = .0001).

CONCLUSION

Calcium stone-forming patients have lower mean levels of vitamin D and a higher percentage of hypovitaminosis D than in non-stone-forming patients. This was only related to increased iPTH levels, with urine calcium and other lithogenic parameters having no obvious effect.

Combined vitamin D and calcium supplementation in vitamin D inadequate patients with urolithiasis: Impact on hypercalciuria and de novo stone formation

INTRODUCTION

We examined the effect of combined vitamin D and calcium supplementation (VDCS) on urinary calcium excretion and de novo stone formation in vitamin D inadequate (VDI) urolithiasis patients.

METHODS

We retrospectively reviewed the data of VDI patients (serum 25-hydroxyvitamin D <75 nmol/L) followed at a tertiary stone centre between September 2009 and December 2014. VDI patients with history of urolithiasis, who were placed on VDCS for abnormal bone mineral density or hyperoxaluria, were included. Hypercalciuric patients and patients on thiazide diuretics were excluded. Metabolic stone workup and two 24-hour urine collections were performed before and after VDCS.

RESULTS

In total, we included 34 patients, with a mean age of 54.8 years and a mean body mass index of 25.7 kg/m(2). After VDCS, there was a significant increase in the mean serum 25-hydroxyvitamin D (52.0 vs. 66.4 nmol/L, p < 0.001) and the mean urinary calcium excretion (3.80 vs. 5.64 mmol/d, p < 0.001). Eight (23.5%) patients developed de novo hypercalciuria. After a median follow-up of 39 (range: 7-60) months, 50% of hypercalciuric patients developed stones compared with 11.5% of non-hypercalciuric patients (p = 0.038).

CONCLUSION

This study showed a significant effect of combined VDCS on mean urinary calcium excretion, de novo hypercalciuria, and stone development in VDI patients with history of urolithiasis. Therefore, VDI urolithiasis patients receiving VDCS are advised to have monitoring with 24-hour urine collections and imaging studies. Although small, our sample size was good enough to validate the statistical outcomes. Prospective studies are needed to confirm these results.

Idiopathic Calcium Nephrolithiasis and Hypovitaminosis D: A Case-control Study

OBJECTIVE

To investigate the association between vitamin D deficiency (25-hydroxyvitamin D <20 ng/mL) and idiopathic calcium nephrolithiasis (ICN).

METHODS

A total of 884 patients with ICN (363 males, mean age of 51 ± 14) and 967 controls (162 males, mean age of 59 ± 15) from an area with no food fortification policy were considered following a case-control study design. Patients were enrolled at a third-level outpatient stone clinic. Controls were selected from a laboratory database after exclusion of those with nephrolithiasis, bone, endocrine, liver, and kidney diseases. Serum 25-hydroxyvitamin-D (25-OH-D), date of test, presence/history of diabetes, and cardiovascular disease including hypertension were recorded for all subjects. Serum parathormone, calcium, phosphorus, and urinary factors of lithogenic risk were available in stone formers (SF). After univariate statistical analysis, propensity score matching with conditional logistic regression was used to control for the possible effects of covariates.

RESULTS

The prevalence of 25-OH-D <20 ng/mL was 56% in SF and 44% in controls (P <.001), with median levels of 18 ng/mL [interquartile range (IQR) of 12-24)] versus 23 ng/mL (IQR of 14-30) (age and sex adjusted P <.001). After a fully adjusted conditional logistic regression analysis, performed on propensity-matched cohorts (442 SF, 442 controls), there was a statistically significant association between vitamin D deficiency and odds of nephrolithiasis (estimated odds ratio of 2.29, confidence interval 95% 1.74-3.02, P <.001). 25-OH-D levels were not different in hypercalciuric and normocalciuric SF (median and IQR of 18 ng/mL and 13-23 vs 19 ng/mL and 13-26, respectively, P = .2).

CONCLUSIONS

SF have lower serum 25-OH-D levels than controls. The role of hypovitaminosis D in the onset of ICN should be better reconsidered.

Implications of vitamin D deficiency in lithiasic patient and in general population

CONTEXT AND OBJECTIVE

Vitamin D deficiency causes problems in mineral metabolism but also overall health. In first place a review of the topic was carried out. Then, in order to contextualize it in lithiasic patient, a study on Vitamin D deficiency and its possible relationship with impaired PTH levels is performed.

EVIDENCES ACQUISITION

A review of topics such as metabolism, epidemiology and the relationship of vitamin D deficiency with several pathologies was performed. Besides a multivariate analysis and a correlation study between vitamin D and PTH levels was conducted in 100 lithiasic patients.

EVIDENCES SYNTHESIS

We present a review of Vitamin D metabolism, receptors and functions, as well as about its valuation methodology and the treatment of its deficiency. Lithiasic patients show a higher vitamin D deficiency than general population. Vitamin D deficiency has been significantly associated with increased PTH levels. In addition, there is enough literature showing a relationship between vitamin D deficiency not only with bone disease, but also with multiple diseases.

CONCLUSION

vitamin D levels should be measured in all lithiasic patients, and those with vitamin D deficiency should be treated.

Association of urinary calcium excretion with serum calcium and vitamin D levels

BACKGROUND AND OBJECTIVES

Population-based data on urinary calcium excretion are scarce. The association of serum calcium and circulating levels of vitamin D [25(OH)D2 or D3] with urinary calcium excretion in men and women from a population-based study was explored.

DESIGN, SETTINGS, PARTICIPANTS, & MEASUREMENTS

Multivariable linear regression was used to explore factors associated with square root-transformed 24-hour urinary calcium excretion (milligrams per 24 hours) taken as the dependent variable with a focus on month-specific vitamin D tertiles and serum calcium in the Swiss Survey on Salt Study.

RESULTS

In total, 624 men and 669 women were studied with mean ages of 49.2 and 47.0 years, respectively (age range=15-95 years). Mean urinary calcium excretion was higher in men than in women (183.05 versus 144.60 mg/24 h; P<0.001). In adjusted models, the association (95% confidence interval) of square root urinary calcium excretion with protein-corrected serum calcium was 1.78 (95% confidence interval, 1.21 to 2.34) mg/24 h per milligram per deciliter in women and 0.59 (95% confidence interval, -0.11 to 1.29) mg/24 h per milligram per deciliter in men. Men in the third 25(OH)D3 tertile had higher square root urinary calcium excretion than men in the first tertile (0.99; 95% confidence interval, 0.36 to 1.63 mg/24 h per nanogram per milliliter), and the corresponding association was 0.32 (95% confidence interval, -0.22 to 0.85) mg/24 h per nanogram per milliliter in women. These sex differences were more marked under conditions of high urinary sodium or urea excretions.

CONCLUSIONS

There was a positive association of serum calcium with urinary calcium excretion in women but not men. Vitamin 25(OH)D3 was associated with urinary calcium excretion in men but not women. These results suggest important sex differences in the hormonal and dietary control of urinary calcium excretion.

Association of vitamin D deficiency, secondary hyperparathyroidism, and heterotopic ossification in spinal cord injury

Our objective was to explore the relationship between low vitamin D, secondary hyperparathyroidism, and heterotopic ossification (HO) in patients with spinal cord injury (SCI). Ninety-six subjects with acute or chronic motor complete SCI participated. Levels of serum vitamin D25(OH), calcium, and intact parathyroid hormone (PTH) were collected, and information regarding nutritional patterns and fracture history was obtained from subjects. Evidence of current or previous HO was ascertained through chart review. Of the 96 subjects, 12 were found to have developed HO, 11 with serum vitamin D25(OH) between 5 and 17 ng/mL. Nine subjects exhibited secondary hyperparathyroidism in the range of 72 to 169 pg/mL. Only one subject demonstrated HO in the absence of low vitamin D. However, many subjects with low vitamin D (5-31 ng/mL) did not have hyperparathyroidism or HO. Statistical testing demonstrated a correlation between hyperparathyroidism and HO (p < 0.001) as well as hyperparathyroidism and vitamin D deficiency (<20 ng/mL). Direct correlation between HO and low vitamin D was not observed, but hyperparathyroidism may increase this risk. We believe that those patients who demonstrate low vitamin D and elevated PTH should be screened for HO in addition to beginning vitamin supplementation. Initiating early treatment of low vitamin D to restore therapeutic levels may prevent development of HO.

A 250 μg/week dose of vitamin D was as effective as a 50 μg/d dose in healthy adults, but a regimen of four weekly followed by monthly doses of 1250 μg raised the risk of hypercalciuria

The risk of vitamin D insufficiency is increased in persons having limited sunlight exposure and dietary vitamin D. Supplementation compliance might be improved with larger doses taken less often, but this may increase the potential for side effects. The objective of the present study was to determine whether a weekly or weekly/monthly regimen of vitamin D supplementation is as effective as daily supplementation without increasing the risk of side effects. Participants were forty-eight healthy adults who were randomly assigned for 3 months to placebo or one of three supplementation regimens: 50 μg/d (2000 IU/d, analysed dose 70 μg/d), 250 μg/week (10 000 IU/week, analysed dose 331 μg/week) or 1250 μg/week (50 000 IU/week, analysed dose 1544 μg/week) for 4 weeks and then 1250 μg/ month for 2 months. Daily and weekly doses were equally effective at increasing serum 25-hydroxyvitamin D, which was significantly greater than baseline in all the supplemented groups after 30 d of treatment. Subjects in the 1250 μg treatment group, who had a BMI >26 kg/m2, had a steady increase in urinary Ca in the first 3 weeks of supplementation, and, overall, the relative risk of hypercalciuria was higher in the 1250 μg group than in the placebo group (P=0·01). Although vitamin D supplementation remains a controversial issue, these data document that supplementing with ≤ 250 mg/week (≤ 10 000 IU/week) can improve or maintain vitamin D status in healthy populations without the risk of hypercalciuria, but 24 h urinary Ca excretion should be evaluated in healthy persons receiving vitamin D3 supplementation in weekly single doses of 1250 μg (50 000 IU).