Serum 25-hydroxyvitamin D level and kidney function decline in a Swiss general adult population

Effects of 25-Hydroxyvitamin D Levels on Renal Function: A Bidirectional Mendelian Randomization Study

CONTEXT

Observational studies investigating the role of vitamin D in renal function have yielded inconsistent results.

OBJECTIVE

We tested whether 25-hydroxyvitamin D (25[OH]D) serum levels are associated with renal function, and inversely, whether altered renal function causes changes in 25(OH)D, using Mendelian randomization (MR).

METHODS

In this two-sample MR study, we used single nucleotide polymorphisms (SNP) associated with 25(OH)D in 443 734 Europeans and evaluated their effects on estimated glomerular filtration rate (eGFR), blood urea nitrogen (BUN), chronic kidney disease (CKD) risk and progression in genome-wide association studies totaling over 1 million Europeans. To control for pleiotropy, we also used SNPs solely in DHCR7, CYP2R1, and GC, all genes with known roles in vitamin D metabolism. We performed a reverse MR, using SNPs for the above indices of renal function to study causal effects on 25(OH)D levels.

RESULTS

We did not find robust evidence supporting effects of 25(OH)D on eGFR, BUN, and CKD or its progression. Our inverse variance weighted MR demonstrated a 0.56 decrease in standardized log-transformed 25(OH)D (95% CI -0.73, -0.41; P = 2.89 × 10-12) per unit increase in log-transformed eGFR. Increased BUN was associated with increased 25(OH)D (β = 0.25, 95% CI 0.15, 0.36; P = 4.12 × 10-6 per unit increase in log-transformed BUN). Finally, genetically predicted CKD conferred a 0.05 increase in standardized log-transformed 25(OH)D level (95% CI 0.04, 0.06; P = 1.06 × 10-13). Other MR methods confirmed the findings of the main analyses.

CONCLUSION

Genetically predicted CKD, increased BUN, and decreased eGFR are associated with increased 25(OH)D levels, but we found no causal effect of 25(OH)D on renal function in Europeans.

Kidney function in patients with bipolar disorder with and without lithium treatment compared with the general population in northern Sweden: results from the LiSIE and MONICA cohorts

BACKGROUND

The clinical relevance of lithium nephropathy is subject to debate. Kidney function decreases with age and comorbidities, and this decline might lead to attribution bias when erroneously ascribed to lithium. We aimed to investigate whether patients with bipolar or schizoaffective disorder had faster decline in estimated glomerular filtration rate (eGFR) compared with the general population, whether observed differences in the steepness of the decline were attributable to lithium, and whether such changes depended on the length of lithium exposure.

METHODS

In this cross-sectional cohort study, we used clinical data from the Lithium-Study into Effects and Side-effects (LiSIE) retrospective cohort study, which included patients with bipolar disorder or schizoaffective disorder whose medical records were reviewed up to Dec 31, 2017, and the WHO Monitoring of Trends and Determinants in Cardiovascular Disease (MONICA) study, covering a representative sample of the general population in northern Sweden aged 25-74 years. The primary outcome was the age-associated decline of creatinine-based eGFR, assessed using linear regression. We adjusted for sex and grouped for different lengths of lithium exposure (never or <1 year, 1-5 years, >5-10 years, and >10 years). For patients with moderate-to-severe kidney disease we identified the underlying nephropathy in the case records.

FINDINGS

From LiSIE, we included 785 patients (498 [63%] female and 287 [37%] male), with a mean age of 49·8 years (SD 13·2; range 25-74). From MONICA, we included 1549 individuals (800 [52%] female and 749 [48%] male), with a mean age of 51·9 years (13·8; 25-74). No ethnicity data were collected. Adjusted for duration of lithium exposure, eGFR declined by 0·57 mL/min/1·73 m²/year (95% CI 0·50-0·63) in patients with bipolar disorder or schizoaffective disorder and by 0·57 mL/min/1·73 m²/year (0·53-0·61) in the reference population. Lithium added 0·54 mL/min/1·73 m² (0·43-0·64) per year of treatment (p<0·0001). After more than 10 years on lithium, decline was significantly steeper than in all other groups including the reference population (p<0·0001). Lithium nephropathy was judged to be the commonest cause of moderate-to-severe chronic kidney disease, but comorbidities played a role. The effect of lithium on eGFR showed a high degree of inter-individual variation.

INTERPRETATION

Steeper eGFR decline in patients with bipolar disorder or schizoaffective disorder can be attributed to lithium, but the trajectory of kidney function decline varies widely. Comorbidities affecting kidneys should be treated assertively as one possible means to affect the trajectory. In patients with a fast trajectory, a trade-off is required between continuing lithium to treat mental health problems and discontinuing lithium for the sake of renal health.

FUNDING

Norrbotten County Research and Learning Fund Sweden, Visare Norr (Northern County Councils Regional Federation Fund), Swedish Kidney Foundation (Njurfonden), Swedish Kidney Association (Njurförbundet), Norrbotten section.

TRANSLATION

For the Swedish translation of the Summary see Supplementary Materials section.

The kidney reabsorption-related Magnesium Depletion Score is associated with increased likelihood of abdominal aortic calcification among US adults

BACKGROUND

Kidney reabsorption has a vital role in magnesium homeostasis. This study aimed to determine the relationship between the kidney reabsorption-related magnesium depletion score (MDS) and abdominal aortic calcification (AAC).

METHODS

We obtained the data of 2640 individuals from the National Health and Nutrition Examination Survey (NHANES) database and analyzed the relationship between MDS and AAC scores. MDS is a scoring system developed to predict status of magnesium deficiency that fully considered the pathophysiological factors influencing the kidneys' reabsorption capability. AAC was quantified by the Kauppila score system based on dual-energy X-ray absorptiometry. We performed stratified analysis and multiple equation regression analysis. R and EmpowerStats were used for data analysis.

RESULTS

A total of 2640 participants were included with the mean AAC score of 1.47 ± 0.07. Participants in higher MDS tended to have higher AAC scores (MDS scored 0: 0.75 (0.56, 0.93), MDS scored 1: 1.02 (0.84, 1.21), MDS scored 2: 2.34 (1.80, 2.87), MDS scored 3: 3.19 (2.46, 3.92), MDS ≥ 4: 4.99 (3.49, 6.49)). Compared with those in the lowest MDS scored 0, the highest subgroup (MDS ≥ 4) was associated with a higher AAC score (β = 4.24, 95% CI: 2.78-5.70, p < 0.001), and the association was not altered (β = 1.81, 95% CI: 0.54-3.09, p = 0.002) after adjusting for numerous covariates. Subgroup analyses showed that stronger associations between MDS and AAC score were detected in adults with lower levels of magnesium intake and older (all p for interaction < 0.05).

CONCLUSIONS

The MDS is a promising tool for identifying individuals with magnesium deficiency status who may benefit from dietary magnesium supplementation to reduce the risks of AAC.

Associations Between 25-Hydroxyvitamin D, Kidney Function, and Insulin Resistance Among Adults in the United States of America

Background

Although many molecular studies have tried to explore the relationship between vitamin D metabolism and kidney function, the association between 25-hydroxyvitamin D [25(OH)D] and kidney function is still controversial. Previous studies reported that low vitamin D status and decreased kidney function were associated with insulin resistance (IR). However, neither of them was confirmed by large population-based studies. This study evaluated the associations between 25(OH)D and kidney function and the associations between both of them and IR among adults in the United States of America (USA).

Methods

We analyzed 36,523 adults from the National Health and Nutrition Examination Survey (NHANES) (2001–2014). Kidney function was assessed by the estimated glomerular filtration rate (eGFR), and IR was assessed by homeostasis model assessment (HOMA-IR). All data were survey-weighted, and corresponding linear regression models were performed to examine the associations.

Results

The mean serum 25(OH)D levels were found to be increased in participants with decreased kidney function (eGFR &lt;90 ml/min/1.73 m2), and each unit of decreased serum 25(OH)D concentrations predicted 0.453 ml/min/1.73 m2 (95% CI: 0.426 to 0.480, p &lt; 0.0001) higher eGFR. In addition, each unit of decreased eGFR was associated with 0.007 higher HOMA-IR, while each unit of decreased 25(OH)D concentrations led to 0.025 higher HOMA-IR.

Conclusions

Serum 25-hydroxyvitamin D concentrations were negatively associated with kidney function. IR appears in the early stage of kidney dysfunction, and both serum 25(OH)D concentrations and kidney function are negatively associated with IR. Clinicians should maintain appropriate serum 25(OH)D concentrations and doses of vitamin D supplements for different populations. The underlying mechanism of these associations still needs more research, especially the negative association between serum 25(OH)D concentrations and kidney function.

Effect of Vitamin D Supplementation on Kidney Function in Adults with Prediabetes: A Secondary Analysis of a Randomized Trial

BACKGROUND AND OBJECTIVES

Low serum 25-hydroxyvitamin D (25[OH]D) concentration has been associated with higher levels of proteinuria and lower levels of eGFR in observational studies. In the Vitamin D and Type 2 Diabetes (D2d) study, we investigated the effect of vitamin D supplementation on kidney outcomes in a population with prediabetes.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Overweight/obese adults with high risk for type 2 diabetes (defined by meeting two of three glycemic criteria for prediabetes) were randomized to vitamin D₃ 4000 IU per day versus placebo. Median duration of treatment was 2.9 years (interquartile range 2.0-3.5 years). Kidney outcomes included (1) worsening in Kidney Disease: Improving Global Outcomes (KDIGO ) risk score (low, moderate, high, very high) on two consecutive follow-up visits after the baseline visit and (2) mean changes in eGFR and urine albumin-to-creatinine ratio (UACR).

RESULTS

Among 2166 participants (mean age 60 years, body mass index 32 kg/m², serum 25(OH)D 28 ng/ml, eGFR 87 ml/min per 1.73 m², UACR 11 mg/g, 79% with hypertension), 10% had moderate, high, or very high KDIGO risk score. Over a median follow-up of 2.9 years, there were 28 cases of KDIGO worsening in the vitamin D group and 30 in the placebo group (hazard ratio, 0.89; 95% confidence interval [95% CI], 0.52 to 1.52]). Mean difference in eGFR from baseline was -1.0 ml/min per 1.73 m² (95% CI, -1.3 to -0.7) in the vitamin D group and -0.1 ml/min per 1.73 m² (95% CI, -0.4 to 0.2) in the placebo group; between-group difference was -1.0 ml/min per 1.73 m² (95% CI, -1.4 to -0.6). Mean difference in UACR was 2.7 mg/g (95% CI, 1.2 to 4.3) in the vitamin D group and 2.0 (95% CI, 0.5 to 3.6) in the placebo group; between-group difference was 0.7 mg/g (95% CI, -1.5 to 2.9).

CONCLUSIONS

Among persons with prediabetes, who were not preselected on the basis of serum 25(OH)D concentration, vitamin D supplementation did not affect progression of KDIGO risk scores and did not have a meaningful effect on change in UACR or eGFR.

Glomerular function in relation to fine airborne particulate matter in a representative population sample

From 1990 until 2017, global air-pollution related mortality increased by 40%. Few studies addressed the renal responses to ultrafine particulate [≤ 2.5 µm (PM2.5)], including black carbon (BC), which penetrate into the blood stream. In a Flemish population study, glomerular filtration estimated from serum creatinine (eGFR) and the urinary albumin-to-creatinine ratio were measured in 2005–2009 in 820 participants (women, 50.7%; age, 51.1 years) with follow-up of 523 after 4.7 years (median). Serum creatinine, eGFR, chronic kidney disease (eGFR < 60 mL/min/1.73 m²) and microalbuminuria (> 3.5/> 2.5 mg per mmol creatinine in women/men) were correlated in individual participants via their residential address with PM_2.5 [median 13.1 (range 0.3–2.9) μg/m³] and BC [1.1 (0.3–18) μg/m³], using mixed models accounting for address clusters. Cross-sectional and longitudinally, no renal outcome was associated with PM_2.5 or BC in models adjusted for sex and baseline or time varying covariables, including age, blood pressure, heart rate, body mass index, plasma glucose, the total-to-HDL serum cholesterol ratio, alcohol intake, smoking, physical activity, socioeconomic class, and antihypertensive treatment. The subject-level geocorrelations of eGFR change with to BC and PM2.5 were 0.13 and 0.02, respectively (P ≥ 0.68). In conclusion, in a population with moderate exposure, renal function was unrelated to ultrafine particulate.

Plasma 25-Hydroxyvitamin D3 Concentrations and Risk of New-Onset Proteinuria in Patients With Hypertension

OBJECTIVE

We aimed to evaluate the relationship of plasma 25-hydroxyvitamin D3 (25[OH]D3) with the risk of new-onset proteinuria and examine the possible effect modifiers in patients with hypertension and without chronic kidney disease at baseline.

METHODS

This is a post hoc analysis of the renal substudy of the China Stroke Primary Prevention Trial. A total of 1655 patients with hypertension, who had plasma 25(OH)D3 measurements, as well as without proteinuria and with an estimated glomerular filtration rate of ≥60 mL/min/1.73 m² at baseline, were included in the present study. The main outcome was new-onset proteinuria, defined as a urine dipstick reading of ≥1+ at the exit visit.

RESULTS

The mean (standard deviation) 25(OH)D3 level at baseline was 18.6 (7.5) ng/mL. The median follow-up duration was 4.4 years. Overall, there was a significant inverse association between plasma 25(OH)D3 and the risk of new-onset proteinuria (per standard deviation increment; [odds ratio] OR: 0.70; 95% confidence interval [CI]: 0.50, 0.97). Accordingly, when 25(OH)D3 was assessed as quartiles, a significantly lower risk of new-onset proteinuria was found in participants in quartiles 3-4 (≥17.8 ng/mL; OR: 0.45; 95% CI: 0.23, 0.87), compared with those in quartile 1 (<13.1 ng/mL). Furthermore, a stronger inverse relationship of plasma 25(OH)D3 and new-onset proteinuria was observed in nondiabetic participants (per standard deviation increment; OR: 0.57; 95% CI: 0.39, 0.83; vs. diabetics: OR: 1.48; 95% CI: 0.67, 3.28; P for interaction = 0.028).

CONCLUSION

There was a significant inverse association between plasma 25(OH)D3 and the risk of proteinuria in patients with hypertension, especially in those without diabetes.

Vitamin D3 reduces risk of cardiovascular and liver diseases by lowering homocysteine levels: double-blinded, randomised, placebo-controlled trial

The objective of this study was to evaluate the effect of vitamin D3 on total homocysteine (tHcy) and C-reactive protein (CRP) levels and liver and kidney function tests in overweight women with vitamin D deficiency. Therefore, a randomised, double-blind placebo, controlled clinical trial was conducted on 100 eligible women. Subjects were randomly divided into two groups: the placebo (n 50) and the vitamin D (n 50) which received 1250 µg vitamin D3 per week for 2 months. The participants' 25-hydroxyvitamin D (25(OH)D), tHcy, CRP, alanine aminotransferase (ALT), aspartate aminotransferase (AST), urea, creatinine and estimated glomerular filtration rate (eGFR) were measured and compared before and after treatment. Results showed that the tHcy, CRP, AST, ALT and eGFR levels after the 2nd month of vitamin D3 intervention were significantly (P < 0·001) decreased and the 25(OH)D, urea and creatinine levels were significantly (P < 0·001) increased in the treatment group. In the placebo group, no significant changes were identified throughout the follow-up period. In conclusion, vitamin D3 intervention with a treatment dose of 1250 µg/week for at least 2 months may help in lowering Hcy and CRP levels and may improve liver function tests, which in turn might help in minimising the risk of CVD and liver diseases among overweight women but negatively affect kidney function.

Gain in adiposity over 3 years is associated with progressive renal decline in multi-ethnic South-east Asians with type 2 diabetes

BACKGROUND

This study evaluated the association between gain in adiposity and renal decline in a large prospective multiethnic South-east Asian cohort with type 2 diabetes mellitus (T2DM).

METHODS

Three years after the baseline visit, 2057 T2DM subjects were recalled for reassessment. The final cohort comprised 1014 subjects and was categorized into tertiles based on changes in body weight (ΔWt), body mass index (ΔBMI), visceral fat area (ΔVFA), and BMI-adjusted VFA (ΔVFA_BMI ). Outcomes included annual and rapid (≥3 mL/min per 1.73 m² per year) decline in estimated glomerular filtration rate (eGFR) and progression of albuminuria.

RESULTS

Participants (mean [±SD] age 57 ± 11 years, 48.8% women, BMI 27.7 ± 5.4 kg/m² ) exhibited a median annual decline in eGFR of 1.0 mL/min per 1.73 m² . Compared with the lower tertiles, Tertile 3 of ΔWt, ΔBMI, ΔVFA, and ΔVFA_BMI had the highest anthropometric increase, albeit of modest magnitude, and this was accompanied by the worst renal outcomes (all P < 0.05). The relationship between annual eGFR decline and Tertile 3 of ΔWt, ΔBMI, and ΔVFA_BMI persisted after multivariate adjustment in men but not in women. In addition, Tertile 3 of ΔWt, ΔBMI, ΔVFA, and ΔVFA_BMI predicted rapid eGFR decline. Anthropometric gains were also associated with progression of albuminuria.

CONCLUSIONS

Modest longitudinal gain in adiposity was associated with progressive renal decline in T2DM patients, suggesting that increased adiposity over time adversely affects renal outcomes. Therefore, a carefully designed weight-neutral or -loss antidiabetic treatment regimen is important when managing T2DM in the clinic.

Negative effect of vitamin D on kidney function: a Mendelian randomization study

Background

The kidney plays a central role in the regulation of vitamin D metabolism. It is not clear, however, whether vitamin D influences kidney function. Previous studies have reported conflicting results, which may have been influenced by reverse causation and residual confounding. We conducted a Mendelian randomization (MR) study to obtain unconfounded estimates of the association between genetically instrumented vitamin D metabolites and estimated glomerular filtration rate (eGFR) as well as the urinary albumin:creatinine ratio (UACR).

Methods

We performed a two-sample MR study based on three single nucleotide variants associated with 25(OH)D levels: rs2282679, rs10741657 and rs12785878, related to the genes GC, CYP2R1 and DHCR7, respectively. Estimates of the allele-dependent effects on serum 25(OH)D and eGFR/UACR were obtained from summary statistics of published genome-wide association meta-analyses. Additionally, we performed a one-sample MR analysis for both 25(OH)D and 1,25(OH)2 D using individual-level data from six cohorts.

Results

The combined MR estimate supported a negative causal effect of log transformed 25(OH)D on log transformed eGFR (β = -0.013, P = 0.003). The analysis of individual-level data confirmed the main findings and also revealed a significant association of 1,25(OH)2 D on eGFR (β = -0.094, P = 0.008). These results show that a 10% increase in serum 25(OH)D levels causes a 0.3% decrease in eGFR. There was no effect of 25(OH)D on UACR (β = 0.032, P = 0.265).

Conclusion

Our study suggests that circulating vitamin D metabolite levels are negatively associated with eGFR. Further studies are needed to elucidate the underlying mechanisms.

Desphospho-uncarboxylated matrix Gla protein is a novel circulating biomarker predicting deterioration of renal function in the general population

Background

Recent studies showing an inverse association between estimated glomerular filtration rate (eGFR), a microvascular trait, and inactive desphospho-uncarboxylated matrix Gla protein (dp-ucMGP) support the hypothesis that after vitamin K-dependent activation, matrix Gla protein (MGP) is renoprotective, but these were limited by their cross-sectional design.

Methods

In 1009 randomly recruited Flemish (50.6% women), we assessed the association between eGFR and plasma dp-ucMGP, using multivariable-adjusted analyses.

Results

From baseline to follow-up 8.9 years later (median), dp-ucMGP increased by 23.0% whereas eGFR decreased by 4.05 mL/min/1.73 m2 (P < 0.001). In 938 participants with baseline eGFR ≥60 mL/min/1.73 m2, the incidence of eGFR <60 mL/min/1.73 m2 at follow-up was 8.0% versus 4.1% in the top versus the bottom halve of baseline dp-ucMGP. For a 5-fold higher plasma dp-ucMGP at baseline, eGFR at follow-up decreased by 3.15 mL/min/1.73 m2 [95% confidence interval (CI) 1.26-5.05; P = 0.001]. The hazard ratio expressing the risk of progression to eGFR <60 mL/min/1.73 m2 was 3.49 (95% CI 1.45-8.40; P = 0.005). The hazard ratio relating the presence of microalbuminuria at follow-up to baseline dp-ucMGP was 4.70 (95% CI 1.57-14.1; P = 0.006).

Conclusions

In conclusion, circulating inactive dp-ucMGP, a biomarker of poor vitamin K status, predicts renal dysfunction. Possible underlying mechanisms include protection by activated MGP against calcification and inhibition of the bone morphogenetic protein-signalling pathway.

Serum 25-hydroxyvitamin D concentration is not associated with glomerular filtration rate in a predominantly obese otherwise healthy population

Evidence from observational studies indicates a role for vitamin D in kidney function and progression to chronic kidney disease. Findings from animal studies have proposed underlying mechanisms including increased activation of the renin-angiotensin system, increased blood pressure, insulin resistance and chronic low-grade inflammation. However, human studies are limited by confounders arising from heterogeneous samples of participants. We examined the relationship between 25(OH)D and estimated glomerular filtration rate (eGFR) in a predominantly obese otherwise healthy and drug-naive population with no history of chronic kidney disease (CKD). One hundred and twenty one non-diabetic (75g oral glucose tolerance test; OGTT) volunteers (70 males and 51 females), aged 18-57 years participated in the study. Median 25(OH)D level was 37nmol/L with no difference by sex. Twenty six participants (21.5%) had 25(OH)D <25 nmol/L, 75 participants (62%) had 25(OH)D of 25-49.99nmol/L, and 20 participants (16.5%) had 25(OH)D ≥50nmol/L. In univariate analysis, 25(OH)D was related negatively to percent body fat and 2-h glucose level post OGTT. Mean (SD) eGFR was 113.1 (14.9)mL/min/1.73m², and in the multivariable analysis, it was related to age, sex, percent body fat and 2-h glucose level post OGTT, but not to 25(OH)D. Furthermore, there was no relationship between eGFR and 25(OH)D across BMI categories. Our data suggest that measuring 25(OH)D in predominantly obese otherwise healthy individuals with no history of CKD may not be beneficial in early recognition of kidney disease.

Vitamin D status in renal transplant recipients living in a low-latitude city: association with body fat, cardiovascular risk factors, estimated glomerular filtration rate and proteinuria

Recent evidence suggests that vitamin D deficiency is associated with CVD, impaired kidney function and proteinuria. To date, no study has evaluated these associations in renal transplant recipients (RTR) adjusting for body adiposity assessed by a ‘gold standard’ method. This study aimed to evaluate the vitamin D status and its association with body adiposity, CVD risk factors, estimated glomerular filtration rate (eGFR) and proteinuria in RTR, living in Rio de Janeiro, Brazil (a low-latitude city (22°54'10"S)), taking into account body adiposity evaluated by dual-energy X-ray absorptiometry (DXA). This cross-sectional study included 195 RTR (114 men) aged 47·6 (sd11·2) years. Nutritional evaluation included anthropometry and DXA. Risk factors for CVD were hypertension, diabetes mellitus, dyslipidaemia and the metabolic syndrome. eGFR was evaluated using the Chronic Kidney Disease Epidemiology Collaboration equation. Serum 25-hydroxyvitamin D (25(OH)D) concentration was used to define vitamin D status as follows: 10 % (n19) had vitamin D deficiency (<16 ng/ml), 43 % (n85) had insufficiency (16–30 ng/ml) and 47 % (n91) had sufficiency (>30 ng/ml). Percentage of body fat (DXA) was significantly associated with vitamin D deficiency independently of age, sex and eGFR. Lower 25(OH)D was associated with higher odds of the metabolic syndrome and dyslipidaemia after adjustment for age, sex and eGFR, but not after additional adjustment for body fat. Hypertension and diabetes were not related to 25(OH)D. Lower serum 25(OH)D was associated with increasing proteinuria and decreasing eGFR even after adjustments for age, sex and percentage of body fat. This study suggests that in RTR of a low-latitude city hypovitaminosis D is common, and is associated with excessive body fat, decreased eGFR and increased proteinuria.

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.

Plasma Vitamin D Level and Change in Albuminuria and eGFR According to Sodium Intake

BACKGROUND AND OBJECTIVES

Low circulating 25-hydroxyvitamin D [25(OH)D] and high sodium intake are both associated with progressive albuminuria and renal function loss in CKD. Both vitamin D and sodium intake interact with the renin-angiotensin-aldosterone system. We investigated whether plasma 25(OH)D or 1,25-dihydroxyvitamin D [1,25(OH)2D] is associated with developing increased albuminuria or reduced renal function and whether these associations depend on sodium intake.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Baseline plasma 25(OH)D and 1,25(OH)2D were measured by liquid chromatography tandem mass spectrometry, and sodium intake was assessed by 24-hour urine collections in the general population-based Prevention of Renal and Vascular End-Stage Disease cohort (n=5051). Two primary outcomes were development of urinary albumin excretion >30 mg/24 h and eGFR (creatinine/cystatin C-based CKD Epidemiology Collaboration) <60 ml/min per 1.73 m(2). Participants with CKD at baseline were excluded. In Cox regression analyses, we assessed associations of vitamin D with developing increased albuminuria or reduced eGFR and potential interaction with sodium intake.

RESULTS

During a median follow-up of 10.4 (6.2-11.4) years, 641 (13%) participants developed increased albuminuria, and 268 (5%) participants developed reduced eGFR. Plasma 25(OH)D was inversely associated with increased albuminuria (fully adjusted hazard ratio [HR] per SD higher, 0.86; 95% confidence interval [95% CI], 0.78 to 0.95; P=0.003) but not reduced eGFR (HR, 0.99; 95% CI, 0.87 to 1.12; P=0.85). There was interaction between 25(OH)D and sodium intake for risk of developing increased albuminuria (P interaction =0.03). In participants with high sodium intake, risk of developing increased albuminuria was inversely associated with 25(OH)D (lowest versus highest quartile: adjusted HR, 1.81; 95% CI, 1.20 to 2.73, P<0.01), whereas this association was nonsignificant in participants with low sodium intake (HR, 1.29; 95% CI, 0.94 to 1.77; P=0.12). Plasma 1,25(OH)2D was not significantly associated with increased albuminuria or reduced eGFR.

CONCLUSIONS

Low plasma 25(OH)D is associated with higher risk of developing increased albuminuria, particularly in individuals with high sodium intake, but not of developing reduced eGFR. Plasma 1,25(OH)2D is not associated with risk of developing increased albuminuria or reduced eGFR.