Comparisons of Serum Vitamin D Levels, Status, and Determinants in Populations With and Without Chronic Kidney Disease Not Requiring Renal Dialysis: A 24-Hour Urine Collection Population-Based Study

Mendelian randomization on the association of obesity with vitamin D: Guangzhou Biobank Cohort Study

BACKGROUND

Mendelian randomization (MR) analyses from the West provide evidence that obesity causes lower 25-hydroxyvitamin D [25(OH)D]. As Asian populations are prone to metabolic disorders at a lower body mass index (BMI), whether the association remains in Asian is unclear. We studied whether obesity causes vitamin D deficiency using MR analysis in Chinese.

METHODS

We used data from the Guangzhou Biobank Cohort Study. A genetic score including seven BMI-related single-nucleotide polymorphisms (n = 15,249) was used as the instrumental variable (IV) for BMI. Two-stage least square regression and conventional multivariable linear regression in 2,036 participants with vitamin D data were used to analyze association of BMI with vitamin D.

RESULTS

Proportion of variation explained by the genetic score was 0.7% and the first stage F-statistic for MR analysis was 103. MR analyses showed that each 1 kg/m² higher BMI was associated with lower 25(OH)D by -2.35 (95% confidence interval (CI) -4.68 to -0.02) nmol/L. In conventional multivariable linear regression, higher BMI was also associated with lower 25(OH)D (β = -0.26 nmol/L per 1 kg/m² increase in BMI, 95% CI -0.46 to -0.06). Sensitivity analyses using two-sample IV analysis and leave-one-out method showed similar results.

CONCLUSION

We have first shown by MR and conventional multivariable linear regression that higher BMI causes vitamin D deficiency in Chinese. Our findings highlight the importance of weight control and suggest that vitamin D supplementation may be needed in individuals with overweight or obesity.

Biomarkers Involved in the Mineral-Bone Disorders Secondary to Chronic Hemodialysis

Introduction. Chronic kidney disease (CKD) is one of the most prevalent public health problems of the elderly population. End-Stage Renal Disease (ESRD)’s most common treatment is dialysis. There are some dissimilarities between the sexes that are apparent in the status and the possible outcomes of CKD. This study aims to shed some light on these somewhat overlooked wwwvariations and their implications.

Materials and methods. We conducted an observational study on subjects with CKD, undergoing hemodialysis for at least 2 years. For participation, we selected an equal number of men and women, which were divided into 2 groups according to gender. Plasma levels of the following parameters were monitored: creatinine, urea, bicarbonate, phosphorus, calcium, alkaline phosphatase, vitamin D, FGF-23 and TNF-alpha. The differences of the variables between the two groups were evaluated using TTEST and CORREL test.

Results. A significant correlation was between the plasma levels of FGF-23 and gender (p =0.02). Regarding the plasmatic levels of urea, besides the expected difference in pre- and post- dialysis levels, we obtained a significant correlation between its post-dialysis value and gender (p =0.045). In regard to the plasmatic levels of the alkaline phosphatase, there was a significant correlation between its value and gender (p =0.01).

Conclusions. There is a significant correlation between the plasmatic levels of creatinine, urea, alkaline phosphatase, vitamin D, FGF-23 and gender. Women present lower levels of creatinine and urea, while men present lower plasmatic levels of vitamin D, alkaline phosphatase and FGF-23.

Welfare receipt and the risk of vitamin D deficiency in Japanese patients on maintenance hemodialysis: a cross-sectional, retrospective study

BACKGROUND

Vitamin D deficiency is often observed in patients undergoing maintenance hemodialysis and is associated with significantly increased risk of overall mortality. Despite reports of poor nutrition/intake, vitamin D status among patients on maintenance hemodialysis receiving welfare remains unknown. This study investigated the vitamin D status in welfare recipients undergoing maintenance hemodialysis.

METHODS

This cross-sectional study investigated vitamin D status among 106 outpatients undergoing maintenance hemodialysis at two medical facilities in Japan. Patients were divided into welfare and non-welfare groups based on their status as of September 2018. Patients were divided into two categories: serum vitamin D deficiency, defined as serum 25(OH)D concentrations < 12 ng/mL, or non-deficiency. Vitamin D deficiency was used as a dependent variable, while welfare receipt was used as the main predictor variable.

RESULTS

Mean [± standard deviation] patient age, median [interquartile range] body mass index, and hemodialysis duration were 66.9 [± 10.8] years, 21.5 [19.6, 24.3] kg/m2, and 7.9 [2.9, 12.3] years, respectively. Among 106 patients, 45 were women (42.5%) and 16 (15.1%) were receiving welfare. The welfare group had a higher diabetes prevalence (P = 0.003) and significantly lower median serum 25-hydroxyvitamin D concentrations (11.5 [8.7, 14.0] vs. 14.8 [11.2, 19.9] ng/mL, P = 0.005). Multiple logistic regression analysis revealed that welfare receipt was a significant risk factor for vitamin D deficiency (odds ratio [95% confidence interval], 4.41 [1.08, 18.07]).

CONCLUSIONS

Welfare recipients undergoing maintenance hemodialysis are at significantly increased risks of vitamin D deficiency compared with patients not receiving welfare.

VITADIAL "Does correction of 25 OH-VITAmin D with cholecalciferol supplementation increase muscle strength in hemoDIALysis patients?": study protocol for a randomized controlled trial

BACKGROUND

Muscle strength decreases as kidney failure progresses. Low muscle strength affects more than 50% of hemodialysis patients and leads to daily life activities impairment. In the general population, numerous studies have linked low 25OH-vitamin D (25OHD) concentrations to the loss of the muscle strength and low physical performances. Data on native vitamin D and muscle function are scarce in the chronic kidney disease (CKD) population, but low 25OHD levels have been associated with poor muscle strength. We present in this article the protocol of an ongoing study named VITADIAL testing if cholecalciferol supplementation in hemodialysis patients with low 25OHD improves their muscle strength.

METHODS/DESIGN

VITADIAL is a prospective open randomized French multicenter study. All patients will have 25OHD levels ≤50nmol/L at randomization. One group will receive 100,000 UI cholecalciferol once a month during 6 months; the other group will receive no treatment during 6 months. In order to randomize patients with 25OHD ≤50nmol/L, supplemented patients will undergo a 3 months wash-out period renewable 3 times (maximum of 12 months wash-out) until 25OHD reaches a level ≤50nmol/L. The main objective of this study is to analyze if a 6-month period of oral cholecalciferol (i.e., native vitamin D) supplementation improves muscle strength of hemodialysis patients with low 25OHD vitamin D levels. Muscle strength will be assessed at 0, 3, and 6 months, by handgrip strength measured with a quantitative dynamometer. Secondary objectives are (1) to analyze 25OHD plasma levels after vitamin D wash-out and/or supplementation, as well as factors associated with 25OHD lowering speed during wash-out, and (2) to analyze if this supplementation improves patient's autonomy, reduces frailty risk, and improves quality of life. Fifty-four patients are needed in each group to meet our main objective.

DISCUSSION

In the general population, around 30 randomized studies analyzed the effects of vitamin D supplementation on muscle strength. These studies had very different designs, sizes, and studied population. Globally, these studies and the meta-analysis of studies favor a beneficial effect of vitamin D supplementation on muscle strength, but this effect is mainly found in the subgroup of aged patients and those with the lowest 25OHD concentrations at inclusion. We reported a positive independent association between 25OHD and handgrip strength in a population of 130 hemodialysis patients in a dose-dependent manner. In our cohort, a plateau effect was observed above 75 nmol/L. Only two randomized studies analyzed the effect of native vitamin D supplementation on muscle strength in hemodialysis patients, but unfortunately, these two studies were underpowered. VITADIAL is a trial specifically designed to assess whether cholecalciferol might benefit to hemodialysis patient's muscle strength.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04262934 . Registered on 10 February 2020 - Retrospectively registered.

Recommendations on the measurement and the clinical use of vitamin D metabolites and vitamin D binding protein - A position paper from the IFCC Committee on bone metabolism

Vitamin D, an important hormone with a central role in calcium and phosphate homeostasis, is required for bone and muscle development as well as preservation of musculoskeletal function. The most abundant vitamin D metabolite is 25-hydroxyvitamin D [25(OH)D], which is currently considered the best marker to evaluate overall vitamin D status. 25(OH)D is therefore the most commonly measured metabolite in clinical practice. However, several other metabolites, although not broadly measured, are useful in certain clinical situations. Vitamin D and all its metabolites are circulating in blood bound to vitamin D binding protein, (VDBP). This highly polymorphic protein is not only the major transport protein which, along with albumin, binds over 99% of the circulating vitamin D metabolites, but also participates in the transport of the 25(OH)D into the cell via a megalin/cubilin complex. The accurate measurement of 25(OH)D has proved a difficult task. Although a reference method and standardization program are available for 25(OH)D, the other vitamin D metabolites still lack this. Interpretation of results, creation of clinical supplementation, and generation of therapeutic guidelines require not only accurate measurements of vitamin D metabolites, but also the accurate measurements of several other "molecules" related with bone metabolism. IFCC understood this priority and a committee has been established with the task to support and continue the standardization processes of vitamin D metabolites along with other bone-related biomarkers. In this review, we present the position of this IFCC Committee on Bone Metabolism on the latest developments concerning the measurement and standardization of vitamin D metabolites and its binding protein, as well as clinical indications for their measurement and interpretation of the results.

The measurement of vitamin D metabolites: part I-metabolism of vitamin D and the measurement of 25-hydroxyvitamin D

It has been more than 80 years since the discovery of vitamin D and its ability to cure rickets in children. Vitamin D is a secosteroid and comes in two distinct forms, vitamin D2 and vitamin D3. During the last 40 years, the synthesis and metabolism of vitamin D were elucidated and more than 50 metabolites of vitamin D have been discovered, though commercial measurement procedures have been developed for only a few of them. The clinical significance of vitamin D in calcium and phosphorus homeostasis is well appreciated. However, recent epidemiological data have indicated that it has several extra-skeletal physiologic actions which are still a matter of scientific debate. Both research findings and the debate around the interpretation of the research results have created increased interest in more measurements of vitamin D. With the ever growing family of measurable vitamin D metabolites and the measuring techniques comes a question: What metabolic product will provide the right answers and which is the best way to measure it. The right choice of analytical technique is connected with the question of which metabolite we aim to measure, what is its serum concentration, and the purpose of the measurement. The aim of the first part of this review is to provide a brief overview of vitamin D metabolism and a more detailed analysis of the existing methods and the status of standardization for the measurement of 25-hydroxyvitamin D.

Antiproteinuria Effect of Calcitriol in Patients With Chronic Kidney Disease and Vitamin D Deficiency: A Randomized Controlled Study

OBJECTIVE

Vitamin D has been demonstrated to lessen proteinuria severity in chronic kidney disease (CKD). Compared with healthy populations, patients with CKD may have lower serum levels of 1,25-dihydroxy vitamin D (1,25-(OH)2 D) and 25-hydroxy vitamin D (25-(OH) D). We investigated the effect of  oral low-dose active vitamin D (calcitriol at 0.25 μg, 3 times weekly) on urinary protein excretion.

DESIGN AND METHODS

We conducted a nonblinded and non-placebo-controlled study. In total, 60 patients with CKD (average estimated glomerular filtration rate of >15 mL/min) who received a stable dose of angiotensin receptor blocker (ARB) or angiotensin-converting enzyme inhibitor (ACEI) were enrolled in this 24-week study. We randomly assigned these patients to the vitamin D group (oral calcitriol at 0.25 μg 3 times weekly with an ACEI or ARB) or the control group (ACEI or ARB). Change in the urine protein/creatinine ratio (uPCR) was the primary endpoint in this study.

RESULTS

The mean baseline uPCRs of the 2 groups were comparable (1.84 ± 0.83 g/g vs. 2.02 ± 0.97 g/g, control vs. vitamin D group; P = .46). After the 24-week treatment, the uPCRs were significantly lower than the baseline values in the vitamin D group (1.35 ± 0.64 g/g; P < .05) but not in the control group. The values of uPCR decreased significantly at 8, 16, and 24 weeks (P < .05 vs. baseline) in the vitamin D group. The values of uPCRs were significantly lower in the vitamin D group than in the control group at 8, 16, and 24 weeks (P < .05). A positive correlation was discovered between reduction in uPCRs at 24-week and baseline 25-(OH) D serum level in the vitamin D group (r = 0.738, P < .001).

CONCLUSION

Supplementary low-dose active vitamin D could reduce proteinuria in CKD patients with low serum 25-(OH) D levels.

Benefit-risk balance of native vitamin D supplementation in chronic hemodialysis: what can we learn from the major clinical trials and international guidelines?

For some years, there has been a great renewal of interest in native vitamin D and its major involvement in osseous and non-osseous effects in the organism. Patients in chronic hemodialysis (CHD) constitute a specific population with different physiopathologic characteristics and needs, since morbidity and mortality are strongly correlated with vitamin D insufficiency. Vitamin D supplementation raises very pertinent questions for which we have only partial answers and we lack solid scientific proof to establish certain truths. Thus, we try through this mini-review to analyze the results of the main randomized clinical trials conducted during the last decade, and to discuss international guidelines concerning native vitamin D supplementation in CHD patients. Seven double-blind randomized clinical trials have evaluated native Vitamin D supplementation in CHD patients. These clinical trials began between 2007 and 2013 and studied relatively small samples of patients with an average of 50. All of these trials are important, but do not provide sufficient scientific proof concerning the advantages, consequences, and secondary effects of native vitamin D supplementation in CHD. None of the European, American, English, Asian, Australian, or Canadian recommendations have specified the targets, doses, duration, or the molecule of vitamin D supplementation in the patient on CHD. In 2017, the long-awaited KDIGO recommendations were published and despite the results of clinical trials conducted, the recommendations on native vitamin D supplementation in CHD were very imprecise and sparse, limited to suggesting correction of any state of vitamin D insufficiency or deficiency.

25-Hydroxyvitamin D Is Associated with Kidney Function: The Dong-gu Study

Although the kidneys play a leading part in the biosynthesis of vitamin D, there is no consensus regarding the relationship of the vitamin D concentration with kidney function. Thus, we aimed to estimate the correlation among 25-hydroxyvitamin D (25(OH)D), estimated glomerular filtration rate (eGFR), and albumin/creatinine ratio (ACR) in participants aged ≥50 y in Korea. This study consisted of 9,166 people who participated in a basic survey of the Dong-gu Study. Following an overnight fast, the blood and urine sample were assessed. The serum 25(OH)D, eGFR, ACR of each subject were measured. When adjusting for covariates and log-transformed ACR (Model III), the lower eGFR value was significantly associated with increasing 25(OH)D levels (<10.0: 71.5[70.5-72.4]; 10.0-14.9: 70.0 [69.5-70.4]; 15.0-19.9: 68.7 [68.3-69.2]; ≥20.0: 67.4 [66.8-67.9] mL/min/1.73 m², p<0.001). When adjusted for the same covariates and log-transformed eGFR (Model III), the lower ACR value was significantly associated with increasing 25(OH)D levels (<10.0: 57.4 [48.0-66.9]; 10.0-14.9: 40.8 [36.5-45.2]; 15.0-19.9: 34.0 [29.5-38.5]; ≥20.0: 34.3 [28.8-39.8] μg/mg creatinine, p<0.001). In conclusion, the mean values of eGFR were significantly decreased with increasing 25(OH)D levels independent of ACR. In additon, the mean values of ACR were significantly decreased with increasing 25(OH)D levels independent of eGFR in participants aged ≥50 y in Korea.

Serum vitamin D in obese and overweight subjects according to estimated glomerular filtration rate

OBJECTIVE

Obesity and renal disease are both associated with low serum 25(OH)D. The aims of the present study were to (a) assess vitamin D status and compare serum vitamin D levels in overweight/obese versus normal-weight individuals according to eGFR and (b) assess the role of 25(OH)D in the development of secondary hyperparathyroidism (SHPT).

DESIGN

Serum 25(OH)D, 1,25(OH)₂D, parathyroid hormone (PTH), calcium, and phosphate were measured in 104 subjects with BMI > 25 kg/m². Participants were categorized according to eGFR (ml/min/1.73m²): G1 ≥ 60 (n = 53), G2 30-59 (n = 35), and G3 15-29 (n = 16). Fifty normal-weight individuals with comparable eGFR served as controls: G1-nw (n = 23), G2-nw (n = 18), and G3-nw (n = 9).

RESULTS

25(OH)D levels were lower in G1 compared to those in G1-nw (21.7 ± 6.5 vs 26.5 ± 7.0 ng/ml, p = 0.005), G2 versus G2-nw (19.0 ± 6.0 vs 25.0 ± 5.2 ng/ml, p = 0.001), and G3 vs G3-nw (15.8 ± 4.7 vs 20.3 ± 4.5 ng/ml, p = 0.030). 1,25(OH)₂D and PTH levels were similar in obese/overweight versus normal-weight individuals in each of the eGFR categories. Factors independently associated with low 25(OH)D levels were BMI > 25 kg/m², lower eGFR, and female gender. Mean 25(OH)D levels were < 30 ng/ml in both overweight and controls, in all eGFR groups. SHPT was universally observed when eGFR was < 30 ml/min/1.73m².

CONCLUSIONS

Lower serum 25(OH)D but similar 1,25(OH)₂D and PTH levels were observed in overweight/obese compared to normal-weight individuals. Even though vitamin D insufficiency was common across all eGFR categories, secondary hyperparathyroidism was more prevalent as eGFR declined.

Vitamin D in Chronic Kidney Disease and Dialysis Patients

Vitamin D deficiency (<20 ng/mL) and insufficiency (20–29 ng/mL) are common among patients with chronic kidney disease (CKD) or undergoing dialysis. In addition to nutritional and sunlight exposure deficits, factors that affect vitamin D deficiency include race, sex, age, obesity and impaired vitamin D synthesis and metabolism. Serum 1,25(OH)₂D levels also decrease progressively because of 25(OH)D deficiency, together with impaired availability of 25(OH)D by renal proximal tubular cells, high fibroblast growth factor (FGF)-23 and decreased functional renal tissue. As in the general population, this condition is associated with increased morbidity and poor outcomes. Together with the progressive decline of serum calcitriol, vitamin D deficiency leads to secondary hyperparathyroidism (SHPT) and its complications, tertiary hyperparathyroidism and hypercalcemia, which require surgical parathyroidectomy or calcimimetics. Kidney Disease Outcomes Quality Initiative (KDOQI) and Kidney Disease Improving Global Outcomes (KDIGO) experts have recognized that vitamin D insufficiency and deficiency should be avoided in CKD and dialysis patients by using supplementation to prevent SHPT. Many vitamin D supplementation regimens using either ergocalciferol or cholecalciferol daily, weekly or monthly have been reported. The benefit of native vitamin D supplementation remains debatable because observational studies suggest that vitamin D receptor activator (VDRA) use is associated with better outcomes and it is more efficient for decreasing the serum parathormone (PTH) levels. Vitamin D has pleiotropic effects on the immune, cardiovascular and neurological systems and on antineoplastic activity. Extra-renal organs possess the enzymatic capacity to convert 25(OH)D to 1,25(OH)₂D. Despite many unanswered questions, much data support vitamin D use in renal patients. This article emphasizes the role of native vitamin D replacement during all-phases of CKD together with VDRA when SHPT persists.

Association between Parathyroid Hormone, 25 (OH) Vitamin D, and Chronic Kidney Disease: A Population-Based Study

Identification of the accurate risk factor for CKD remains mandatory to combat the high prevalence of diseases. Growing evidence suggests the association of serum vitamin D with diverse health conditions. However, the relationship between vitamin D, intact parathyroid hormone (PTH), and calcium-phosphate metabolism and development of CKD remains controversial. We conduct this cross-sectional observational study to investigate the association between serum 25 (OH) vitamin D, intact PTH, and calcium and phosphate levels with eGFR and albuminuria, as a surrogate marker of CKD, in a community population. A total of 4080 participants were recruited. The mean age was 58.4 ± 13.3 years and 1480 (36.3%) were men. The mean eGFR was 94.1 ± 26.3 mL/min/1.73 m². The prevalence of CKD was 19.8%. Serum 25 (OH) vitamin D and log intact PTH levels were inversely correlated with eGFR but positively correlated with log albuminuria. Logistic regression analysis identified the log intact PTH as an independent factor associated with eGFR ≤ 60 mL/min/1.73 m² and proteinuria. This association was consistent when serum intact PTH was analyzed as continuous as well as categorical variables (as hyperparathyroidism). The relationship remains significant using resampling subset analysis with comparable baseline characteristics and adjustment for 25 (OH) vitamin D, calcium, and phosphate levels. This finding warranted further research to clarify the causal relationship of PTH/25 (OH) vitamin D with the risk of CKD in the general population.

Vitamin D status and its predictors in New Zealand aged-care residents eligible for a government-funded universal vitamin D supplementation programme

OBJECTIVE

The provision of prescribed vitamin D to all aged-care residents has been implemented in New Zealand as part of a government-led falls prevention programme. To our knowledge, there has been no evaluation of this universal programme on vitamin D status and functional and health outcomes. Thus, we aimed to determine 25-hydroxyvitamin D (25(OH)D) concentrations and their predictors in aged-care residents across the country and to investigate whether the government-funded programme was associated with adequate vitamin D status.

DESIGN

Cross-sectional survey of sociodemographic, biochemical, anthropometric, dietary and health characteristics. Blood samples were analysed for serum 25(OH)D and other biochemical measures. Multiple regression was used to examine predictors of vitamin D status.

SETTING

Sixteen residential aged-care facilities throughout New Zealand.

SUBJECTS

Residents aged ≥60 years with residency duration >12 weeks (n 309).

RESULTS

Mean serum 25(OH)D was 89·9 (95 % CI 85·2, 94·5) nmol/l and monthly supplements (1250 µg (50 000 IU)) were taken by 75 % of all residents. Of those not taking a funded supplement, 65·3 % had serum 25(OH)D 125 nmol/l.

CONCLUSIONS

Residents taking supplemental vitamin D had adequate vitamin D status; however monitoring of long-term supplementation should be considered, due to the high proportion of participants with high serum 25(OH)D levels.

Relative importance of the determinants of serum levels of 25-hydroxy vitamin D in patients with chronic kidney disease

INTRODUCTION

The cause of vitamin D deficiency in chronic kidney disease (CKD) is probably multi-factorial; however, the relative importance of each potential determinant is uncertain.

AIMS

To determine factors associated with serum levels of 25-hydroxy vitamin D (25OHD) and their relative importance in a cohort of pre-dialysis CKD patients.

MATERIAL AND METHODS

Incident patients admitted to a CKD outpatient clinic were included. Those who were receiving vitamin D supplements or anticonvulsants were excluded. In addition to demographic and clinical data, information about outdoor physical activity, season of blood collection, prescription of statins, anti-angiotensin drugs and xanthine-oxidase inhibitors were included as potential determinants. Johnson's relative weights analysis was used to estimate the relative importance of each potential determinant and the results were expressed as percentage contribution to multiple R.

RESULTS

The study group consisted of 397 patients, 30 of whom were excluded. The mean serum level of 25OHD was 13.7±7.4ng/ml, and 81% of patients had serum levels lower than 20ng/ml. By multiple linear regression and relative weights analyses, the best determinants of low serum 25OHD levels and their relative importance were: higher proteinuria (28.5%), old age (21.4%), low physical activity (19.4%), female gender (19.3%) and low serum bicarbonate levels (11.4%).

CONCLUSIONS

Proteinuria and age are the determinants with the highest relative importance for predicting 25OHD levels in CKD patients.

Methodology used in studies reporting chronic kidney disease prevalence: a systematic literature review

Background

Many publications report the prevalence of chronic kidney disease (CKD) in the general population. Comparisons across studies are hampered as CKD prevalence estimations are influenced by study population characteristics and laboratory methods.

Methods

For this systematic review, two researchers independently searched PubMed, MEDLINE and EMBASE to identify all original research articles that were published between 1 January 2003 and 1 November 2014 reporting the prevalence of CKD in the European adult general population. Data on study methodology and reporting of CKD prevalence results were independently extracted by two researchers.

Results

We identified 82 eligible publications and included 48 publications of individual studies for the data extraction. There was considerable variation in population sample selection. The majority of studies did not report the sampling frame used, and the response ranged from 10 to 87%. With regard to the assessment of kidney function, 67% used a Jaffe assay, whereas 13% used the enzymatic assay for creatinine determination. Isotope dilution mass spectrometry calibration was used in 29%. The CKD-EPI (52%) and MDRD (75%) equations were most often used to estimate glomerular filtration rate (GFR). CKD was defined as estimated GFR (eGFR) <60 mL/min/1.73 m² in 92% of studies. Urinary markers of CKD were assessed in 60% of the studies. CKD prevalence was reported by sex and age strata in 54 and 50% of the studies, respectively. In publications with a primary objective of reporting CKD prevalence, 39% reported a 95% confidence interval.

Conclusions

The findings from this systematic review showed considerable variation in methods for sampling the general population and assessment of kidney function across studies reporting CKD prevalence. These results are utilized to provide recommendations to help optimize both the design and the reporting of future CKD prevalence studies, which will enhance comparability of study results.

Vitamin D status and cholecalciferol supplementation in chronic kidney disease patients: an Italian cohort report

This study investigated the factors associated with hypovitaminosis D, in a cohort of 405 prevalent patients with chronic kidney disease (CKD) stages 2–4, living in Italy and followed-up in tertiary care. The effect of cholecalciferol 10,000 IU once-a-week for 12 months was evaluated in a subgroup of 100 consecutive patients with hypovitaminosis D. Vitamin D deficiency was observed in 269 patients (66.4%) whereas vitamin D insufficiency was found in 67 patients (16.5%). In diabetic patients, 25-hydroxyvitamin D deficiency was detected in 80% of cases. In patients older than 65 years, the prevalence of hypovitaminosis D was 89%. In the univariate analysis, 25-hydroxyvitamin D was negatively related to age, parathyroid hormone (PTH), proteinuria, and Charlson index, while a positive relationship has emerged with hemoglobin level. On multiple regression analysis, only age and PTH levels were independently associated with 25-hydroxyvitamin D levels. No relationship emerged between vitamin D deficiency and renal function. Serum levels of 25-hydroxyvitamin D or prevalence of hypovitaminosis D did not differ between patients on a free-choice diet and on a renal diet, including low-protein, low-phosphorus regimens. Twelve-month oral cholecalciferol administration increased 25-hydroxyvitamin D and reduced PTH serum levels. In summary, hypovitaminosis D is very prevalent in CKD patients (83%) in Italy, and it is similar to other locations. PTH serum levels and age, but not renal function, are the major correlates of hypovitaminosis D. Implementation of renal diets is not associated with higher risk of vitamin D depletion. Oral cholecalciferol administration increased 25-hydroxyvitamin D and mildly reduced PTH serum levels. Oral cholecalciferol supplementation should be recommended as a regular practice in CKD patients, also when serum 25-hydroxyvitamin D determination is not available or feasible.

Low levels of vitamin D are associated with multimorbidity: results from the LifeLines Cohort Study

BACKGROUND

The prevalence of multimorbidity (≥ 1 disease within an individual) is rapidly increasing. So far, studies on the relationship between vitamin D and morbidity are mainly focusing on effects on single disease domains only, while vitamin D biology is associated with several diseases throughout the human body.

METHODS

We studied 8,726 participants from the LifeLines Cohort Study (a cross-sectional, population-based cohort study) and used the self-developed composite morbidity score to study the association between vitamin D levels and multimorbidity.

RESULTS

Study participants (mean age 45 ± 13 years, 73% females) had a mean plasma vitamin D level of 59 ± 22 nmol/L. In participants aged between 50 and 60 years, 58% had ≥ 2 affected disease domains, while morbidity score increased with age (70-80 years: 82% morbidity score > 1; > 80 years: 89% morbidity score > 1). Each incremental reduction by 1 standard deviation (SD) of vitamin D level was associated with an 8% higher morbidity score (full model OR 0.92, 95% CI 0.88-0.97, P = 0.001). Participants with vitamin D levels < 25 nmol/L were at highest risk for increasing morbidity prevalence (versus > 80 nmol/L, OR 1.34, 95% CI 1.07-1.67, P = 0.01).

CONCLUSIONS

Low levels of vitamin D are associated with higher prevalence of multimorbidity, especially in participants with vitamin D levels < 25 nmol/L. Collectively, our results favor a general, rather than an organ-specific, approach when assessing the impact of vitamin D deficiency.