Thyroid function and risk of all-cause and cardiovascular mortality: a prospective population-based cohort study

PURPOSE

Although thyroid hormones are irrefutably implicated in cardiovascular physiology, the impact of within-reference range variations of thyroid function on cardiovascular disease (CVD) remains unclear. Elucidating this is important, since it could foster preventive treatment and reduce global CVD burden. We therefore investigated the impact of within-reference range variations of thyroid function on all-cause and cardiovascular mortality.

METHODS

We included community-dwelling individuals aged 28-75 years from a prospective cohort study, without known use of thyroid-affecting therapy and with thyrotropin within reference range. Associations of thyroid function with mortality were quantified using Cox models and adjusted for sociodemographic and cardiovascular risk factors.

RESULTS

Mean (SD) age of the 6,054 participants (52.0% male) was 53.3 (12.0) years. During 47,594 person-years of follow-up, we observed 380 deaths from all causes and 103 from CVDs. Although higher thyrotropin was not associated with all-cause mortality (adjusted HR 1.02, 95% CI 0.92-1.14), point estimates for cardiovascular mortality diverged toward increased risk in younger (<72 years) participants (1.31, 1.00-1.72) and decreased risk in elderly (≥72 years) (0.77, 0.56-1.06). Higher free thyroxine (FT₄) was associated with all-cause mortality (1.18, 1.07-1.30) and with cardiovascular mortality only in elderly (1.61, 1.19-2.18), but not in younger participants (1.03, 0.78-1.34). Higher free triiodothyronine (FT₃) was associated with all-cause mortality in females only (1.18, 1.02-1.35). FT₃ was not associated with cardiovascular mortality (0.91, 0.70-1.18).

CONCLUSIONS

Community-dwelling elderly individuals with high-normal thyroid function are at increased risk of all-cause and cardiovascular mortality, reinforcing the need of redefining the current reference ranges of thyroid function.

Aorto-Iliac Artery Calcification and Graft Outcomes in Kidney Transplant Recipients

While the association of vascular calcification with inferior patient outcomes in kidney transplant recipients is well-established, the association with graft outcomes has received less attention. With this dual-centre cohort study, we aimed to determine the clinical impact of recipient pre-transplant aorto-iliac calcification, measured on non-contrast enhanced computed tomography (CT)-imaging within three years prior to transplantation (2005–2018). We included 547 patients (61.4% male, age 60 (interquartile range 51–68) years), with a median follow-up of 3.1 (1.4–5.2) years after transplantation. The aorto-iliac calcification score (CaScore) was inversely associated with one-year estimated-glomerular filtration rate (eGFR) in univariate linear regression analysis (standard β −3.3 (95% CI −5.1 to −1.5, p < 0.0001), but not after adjustment for potential confounders, including donor and recipient age (p = 0.077). In multivariable Cox regression analyses, a high CaScore was associated with overall graft failure (p = 0.004) and death with a functioning graft (p = 0.002), but not with death-censored graft failure and graft function decline. This study demonstrated that pre-transplant aorto-iliac calcification is associated with one-year eGFR in univariate, but not in multivariable linear regression analyses. Moreover, this study underlines that transplantation in patients with a high CaScore does not result in earlier transplant function decline or worse death censored graft survival, although ongoing efforts for the prevention of death with a functioning graft remain essential.

Functional vitamin K status and risk of incident chronic kidney disease and microalbuminuria: a prospective general population-based cohort study

Background

Circulating desphospho-uncarboxylated matrix γ-carboxyglutamate (Gla) protein (dp-ucMGP), a marker of vitamin K status, is associated with renal function and may serve as a potentially modifiable risk factor for incident chronic kidney disease (CKD). We aimed to assess the association between circulating dp-ucMGP and incident CKD.

Methods

We included 3969 participants with a mean age of 52.3 ± 11.6 years, of whom 48.0% were male, enrolled in the general population–based Prevention of REnal and Vascular ENd-stage Disease study. Study outcomes were incident CKD, defined as either development of an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m² or microalbuminuria. Associations of dp-ucMGP with these outcomes were quantified using Cox proportional hazards models and were adjusted for potential confounders.

Results

Median plasma dp-ucMGP was 363 [interquartile range (IQR) 219–532] pmol/L and mean serum creatinine- and serum cystatin C-based eGFR (eGFR_SCr-SCys) was 95.4 ± 21.8 mL/min/1.73 m². During 7.1 years of follow-up, 205 (5.4%) participants developed incident CKD and 303 (8.4%) developed microalbuminuria. For every doubling of plasma dp-ucMGP, hazard ratios for the development of incident CKD and microalbuminuria were 1.85 [95% confidence interval (CI) 1.59–2.16; P < 0.001] and 1.19 (95% CI 1.07–1.32; P = 0.001), respectively. These associations lost significance after adjustment for baseline eGFR_SCr-SCys [0.99 (95% CI 0.88–1.12; P = 0.86)] and baseline age [1.03 (95% CI 0.94–1.14; P = 0.50)], respectively.

Conclusions

The associations of plasma dp-ucMGP with incident CKD and microalbuminuria were driven by the respective baseline effects of renal function and age.

Methylmalonic acid, vitamin B12, renal function, and risk of all-cause mortality in the general population: results from the prospective Lifelines-MINUTHE study

BACKGROUND

Methylmalonic acid (MMA) is best known for its use as a functional marker of vitamin B12 deficiency. However, MMA concentrations not only depend on adequate vitamin B12 status, but also relate to renal function and endogenous production of propionic acid. Hence, we aimed to investigate to what extent variation in MMA levels is explained by vitamin B12 and eGFR and whether MMA levels are associated with mortality if vitamin B12 and eGFR are taken into account.

METHODS

A total of 1533 individuals (aged 60-75 years, 50% male) were included from the Lifelines Cohort and Biobank Study. Individuals were included between 2006 and 2013, and the total follow-up time was 8.5 years.

RESULTS

Median [IQR] age of the study population was 65 [62-69] years, 50% was male. At baseline, median MMA concentration was 170 [138-216] nmol/L, vitamin B12 290 [224-362] pmol/L, and eGFR 84 [74-91] mL/min/1.73 m2. Log₂ vitamin B12, log₂ eGFR, age, and sex were significantly associated with log₂ MMA in multivariable linear regression analyses (model R² = 0.22). After a total follow-up time of 8.5 years, 72 individuals had died. Log₂ MMA levels were significantly associated with mortality (hazard ratio [HR] 1.67 [95% CI 1.25-2.22], P < 0.001). Moreover, we found a significant interaction between MMA and eGFR with respect to mortality (P_interaction < 0.001).

CONCLUSIONS

Only 22% of variation in MMA levels was explained by vitamin B12, eGFR, age, and sex, indicating that a large part of variation in MMA levels is attributable to other factors (e.g., catabolism, dietary components, or gut microbial production). Higher MMA levels are associated with an increased risk for mortality, independent of vitamin B12, eGFR, and sex. This association was more pronounced in individuals with impaired renal function.

Pre-Transplant Plasma Potassium as a Potential Risk Factor for the Need of Early Hyperkalaemia Treatment after Kidney Transplantation: A Cohort Study

INTRODUCTION

Plasma potassium (K+) abnormalities are common among patients with chronic kidney disease and are associated with higher rates of death, major adverse cardiac events, and hospitalization in this population. Currently, no guidelines exist on how to handle pre-transplant plasma K+ in renal transplant recipients (RTR).

OBJECTIVE

The aim of this study is to examine the relation between pre-transplant plasma K+ and interventions to resolve hyperkalaemia within 48 h after kidney transplantation.

METHODS

In a single-centre cohort study, we addressed the association between the last available plasma K+ level before transplantation and the post-transplant need for dialysis or use of K+-lowering medication to resolve hyperkalaemia within 48 h after renal transplantation using multivariate logistic regression analysis.

RESULTS

151 RTR were included, of whom 51 (33.8%) patients received one or more K+ interventions within 48 h after transplantation. Multivariate regression analysis revealed that a higher pre-transplant plasma K+ was associated with an increased risk of post-transplant intervention (odds ratio 2.2 [95% CI: 1.1-4.4]), independent of donor type (deceased or living) and use of K+-lowering medication within 24 h prior to transplantation).

CONCLUSIONS

This study indicates that a higher pre-transplant plasma K+ is associated with a higher risk of interventions necessary to resolve hyperkalaemia within 48 h after renal transplantation. Further research is recommended to determine a cutoff level for pre-transplant plasma K+ that can be used in practice.

Calciprotein particle inhibition explains magnesium-mediated protection against vascular calcification

Background

Phosphate (Pi) toxicity is a strong determinant of vascular calcification development in chronic kidney disease (CKD). Magnesium (Mg²⁺) may improve cardiovascular risk via vascular calcification. The mechanism by which Mg²⁺ counteracts vascular calcification remains incompletely described. Here we investigated the effects of Mg²⁺ on Pi and secondary crystalline calciprotein particles (CPP2)-induced calcification and crystal maturation.

Methods

Vascular smooth muscle cells (VSMCs) were treated with high Pi or CPP2 and supplemented with Mg²⁺ to study cellular calcification. The effect of Mg²⁺ on CPP maturation, morphology and composition was studied by medium absorbance, electron microscopy and energy dispersive spectroscopy. To translate our findings to CKD patients, the effects of Mg²⁺ on calcification propensity (T₅₀) were measured in sera from CKD patients and healthy controls.

Results

Mg²⁺ supplementation prevented Pi-induced calcification in VSMCs. Mg²⁺ dose-dependently delayed the maturation of primary CPP1 to CPP2 in vitro. Mg²⁺ did not prevent calcification and associated gene and protein expression when added to already formed CPP2. Confirmatory experiments in human serum demonstrated that the addition of 0.2 mmol/L Mg²⁺ increased T₅₀ from healthy controls by 51 ± 15 min (P < 0.05) and CKD patients by 44 ± 13 min (P < 0.05). Each further 0.2 mmol/L addition of Mg²⁺ led to further increases in both groups.

Conclusions

Our results demonstrate that crystalline CPP2 mediates Pi-induced calcification in VSMCs. In vitro, Mg²⁺ delays crystalline CPP2 formation and thereby prevents Pi-induced calcification.

Plasma C-Peptide and Risk of Developing Type 2 Diabetes in the General Population

C-peptide measurement may represent a better index of pancreatic β-cell function compared to insulin. While insulin is mainly cleared by liver, C-peptide is mainly metabolized by kidneys. The aim of our study was to evaluate the association between baseline plasma C-peptide level and the development of type 2 diabetes independent of glucose and insulin levels and to examine potential effect-modification by variables related to kidney function. We included 5176 subjects of the Prevention of Renal and Vascular End-Stage Disease study without type 2 diabetes at baseline. C-peptide was measured in plasma with an electrochemiluminescent immunoassay. Cox proportional hazards regression was used to evaluate the association between C-peptide level and type 2 diabetes development. Median C-peptide was 722 (566-935) pmol/L. During a median follow-up of 7.2 (6.0-7.7) years, 289 individuals developed type 2 diabetes. In multivariable-adjusted Cox regression models, we observed a significant positive association of C-peptide with the risk of type 2 diabetes independent of glucose and insulin levels (hazard ratio (HR): 2.35; 95% confidence interval (CI): 1.49-3.70). Moreover, we found significant effect modification by hypertension and albuminuria (p < 0.001 and p = 0.001 for interaction, respectively), with a stronger association in normotensive and normo-albuminuric subjects and absence of an association in subjects with hypertension or albuminuria. In this population-based cohort, elevated C-peptide levels are associated with an increased risk of type 2 diabetes independent of glucose, insulin levels, and clinical risk factors. Elevated C-peptide level was not independently associated with an increased risk of type 2 diabetes in individuals with hypertension or albuminuria.

Comparison of two methods for the assessment of intra-erythrocyte magnesium and its determinants: Results from the LifeLines cohort study

BACKGROUND

Direct methods for the assessment of intra-erythrocyte magnesium (dIEM) require extensive sample preparation, making them labor intensive. An alternative, less labor intensive method is indirect calculation of intra-erythrocyte magnesium (iIEM). We compared dIEM and iIEM and studied determinants of dIEM and iIEM, plasma magnesium and 24-h urinary magnesium excretion in a large population-based cohort study.

METHODS

dIEM and iIEM were measured using a validated inductively coupled plasma mass spectrometry (ICP-MS) method in 1669 individuals from the second screening from the LifeLines Cohort Study. We used linear regression analyses to study the determinants of IEM, plasma magnesium and 24-h urinary magnesium excretion.

RESULTS

Mean dIEM and iIEM were 0.20 ± 0.04 mmol/10¹² cells and 0.25 ± 0.04 mmol/10¹² cells, respectively. We found a strong correlation between dIEM and iIEM (r = 0.75). Passing-Bablok regression analyses showed an intercept of 0.015 (95% CI: 0.005; 0.023) and a slope of 1.157 (95% CI: 1.109; 1.210). In linear regression analyses, plasma levels of total- and LDL -cholesterol, and triglycerides were positively associated dIEM, iIEM, and plasma magnesium, while glucose and HbA1c were inversely associated with plasma magnesium.

CONCLUSIONS

We observed a strong correlation between dIEM and iIEM, suggesting that iIEM is a reliable alternative for the labor intensive dIEM method.

Plasma cadmium is associated with increased risk of long-term kidney graft failure

The kidney is one of the most sensitive organs to cadmium-induced toxicity, particularly in conditions of long-term oxidative stress. We hypothesized that, in kidney transplant recipients, nephrotoxic exposure to cadmium represents an overlooked hazard for optimal graft function. To test this, we performed a prospective cohort study and included 672 outpatient kidney transplant recipients with a functioning graft of beyond one year. The median plasma cadmium was 58 ng/L. During a median 4.9 years of follow-up, 78 kidney transplant recipients developed graft failure with a significantly different distribution across tertiles of plasma cadmium (13, 26, and 39 events, respectively). Plasma cadmium was associated with an increased risk of graft failure (hazard ratio 1.96, 95% confidence interval 1.56‒2.47 per log₂ ng/L). Similarly, a dose-response relationship was observed over increasing tertiles of plasma cadmium, after adjustments for potential confounders (donor, recipient, transplant and lifestyle characteristics), robust in both competing risk and sensitivity analyses. These findings were also consistent for kidney function decline (graft failure or doubling of serum creatinine). Thus, plasma cadmium is independently associated with an increased risk of long-term kidney graft failure and decline in kidney function. Further studies are needed to investigate whether exposure to cadmium represents an otherwise overlooked modifiable risk factor for adverse long-term graft outcomes in different populations.

Iron deficiency after kidney transplantation

Iron deficiency (ID) is highly prevalent in kidney transplant recipients (KTRs) and has been independently associated with an excess mortality risk in this population. Several causes lead to ID in KTRs, including inflammation, medication and an increased iron need after transplantation. Although many studies in other populations indicate a pivotal role for iron as a regulator of the immune system, little is known about the impact of ID on the immune system in KTRs. Moreover, clinical trials in patients with chronic kidney disease or heart failure have shown that correction of ID, with or without anaemia, improves exercise capacity and quality of life, and may improve survival. ID could therefore be a modifiable risk factor to improve graft and patient outcomes in KTRs; prospective studies are warranted to substantiate this hypothesis.

Dietary potassium and the kidney: lifesaving physiology

Potassium often has a negative connotation in Nephrology as patients with chronic kidney disease (CKD) are prone to develop hyperkalaemia. Approaches to the management of chronic hyperkalaemia include a low potassium diet or potassium binders. Yet, emerging data indicate that dietary potassium may be beneficial for patients with CKD. Epidemiological studies have shown that a higher urinary potassium excretion (as proxy for higher dietary potassium intake) is associated with lower blood pressure (BP) and lower cardiovascular risk, as well as better kidney outcomes. Considering that the composition of our current diet is characterized by a high sodium and low potassium content, increasing dietary potassium may be equally important as reducing sodium. Recent studies have revealed that dietary potassium modulates the activity of the thiazide-sensitive sodium-chloride cotransporter in the distal convoluted tubule (DCT). The DCT acts as a potassium sensor to control the delivery of sodium to the collecting duct, the potassium-secreting portion of the kidney. Physiologically, this allows immediate kaliuresis after a potassium load, and conservation of potassium during potassium deficiency. Clinically, it provides a novel explanation for the inverse relationship between dietary potassium and BP. Moreover, increasing dietary potassium intake can exert BP-independent effects on the kidney by relieving the deleterious effects of a low potassium diet (inflammation, oxidative stress and fibrosis). The aim of this comprehensive review is to link physiology with clinical medicine by proposing that the same mechanisms that allow us to excrete an acute potassium load also protect us from hypertension, cardiovascular disease and CKD.

Effects of Potassium or Sodium Supplementation on Mineral Homeostasis: A Controlled Dietary Intervention Study

CONTEXT

Although dietary potassium and sodium intake may influence calcium-phosphate metabolism and bone health, the effects on bone mineral parameters, including fibroblast growth factor 23 (FGF23), are unclear.

OBJECTIVE

Here, we investigated the effects of potassium or sodium supplementation on bone mineral parameters.

DESIGN, SETTING, PARTICIPANTS

We performed a post hoc analysis of a dietary controlled randomized, blinded, placebo-controlled crossover trial. Prehypertensive individuals not using antihypertensive medication (n = 36) received capsules containing potassium chloride (3 g/d), sodium chloride (3 g/d), or placebo. Linear mixed-effect models were used to estimate treatment effects.

RESULTS

Potassium supplementation increased plasma phosphate (from 1.10 ± 0.19 to 1.15 ± 0.19 mmol/L, P = 0.004), in line with an increase in tubular maximum of phosphate reabsorption (from 0.93 ± 0.21 to 1.01 ± 0.20 mmol/L, P < 0.001). FGF23 decreased (114.3 [96.8-135.0] to 108.5 [93.5-125.9] RU/mL, P = 0.01), without change in parathyroid hormone and 25-hydroxy vitamin D3. Fractional calcium excretion decreased (from 1.25 ± 0.50 to 1.11 ± 0.46 %, P = 0.03) without change in plasma calcium. Sodium supplementation decreased both plasma phosphate (from 1.10 ± 0.19 to 1.06 ± 0.21 mmol/L, P = 0.03) and FGF23 (from 114.3 [96.8-135.0] to 108.7 [92.3-128.1] RU/mL, P = 0.02). Urinary and fractional calcium excretion increased (from 4.28 ± 1.91 to 5.45 ± 2.51 mmol/24 hours, P < 0.001, and from 1.25 ± 0.50 to 1.44 ± 0.54 %, P = 0.004, respectively).

CONCLUSIONS

Potassium supplementation led to a decrease in FGF23, which was accompanied by increase in plasma phosphate and decreased calcium excretion. Sodium supplementation reduced FGF23, but this was accompanied by decrease in phosphate and increase in fractional calcium excretion. Our results indicate distinct effects of potassium and sodium intake on bone mineral parameters, including FGF23.

CLINICAL TRIAL REGISTRATION NUMBER

NCT01575041.

Lifestyle, Inflammation, and Vascular Calcification in Kidney Transplant Recipients: Perspectives on Long-Term Outcomes

After decades of pioneering and improvement, kidney transplantation is now the renal replacement therapy of choice for most patients with end-stage kidney disease (ESKD). Where focus has traditionally been on surgical techniques and immunosuppressive treatment with prevention of rejection and infection in relation to short-term outcomes, nowadays, so many people are long-living with a transplanted kidney that lifestyle, including diet and exposure to toxic contaminants, also becomes of importance for the kidney transplantation field. Beyond hazards of immunological nature, a systematic assessment of potentially modifiable-yet rather overlooked-risk factors for late graft failure and excess cardiovascular risk may reveal novel targets for clinical intervention to optimize long-term health and downturn current rates of premature death of kidney transplant recipients (KTR). It should also be realized that while kidney transplantation aims to restore kidney function, it incompletely mitigates mechanisms of disease such as chronic low-grade inflammation with persistent redox imbalance and deregulated mineral and bone metabolism. While the vicious circle between inflammation and oxidative stress as common final pathway of a multitude of insults plays an established pathological role in native chronic kidney disease, its characterization post-kidney transplant remains less than satisfactory. Next to chronic inflammatory status, markedly accelerated vascular calcification persists after kidney transplantation and is likewise suggested a major independent mechanism, whose mitigation may counterbalance the excess risk of cardiovascular disease post-kidney transplant. Hereby, we first discuss modifiable dietary elements and toxic environmental contaminants that may explain increased risk of cardiovascular mortality and late graft failure in KTR. Next, we specify laboratory and clinical readouts, with a postulated role within persisting mechanisms of disease post-kidney transplantation (i.e., inflammation and redox imbalance and vascular calcification), as potential non-traditional risk factors for adverse long-term outcomes in KTR. Reflection on these current research opportunities is warranted among the research and clinical kidney transplantation community.

Serum Calcification Propensity and the Risk of Cardiovascular and All-Cause Mortality in the General Population: The PREVEND Study

OBJECTIVE

Vascular calcification contributes to the cause of cardiovascular disease. The calciprotein particle maturation time (T₅₀) in serum, a measure of calcification propensity, has been linked with adverse outcomes in patients with chronic kidney disease, but its role in the general population is unclear. We investigated whether serum T₅₀ is associated with cardiovascular mortality in a large general population-based cohort. Approach and Results: The relationship between serum T₅₀ and cardiovascular mortality was studied in 6231 participants of the PREVEND (Prevention of Renal and Vascular End-Stage Disease) cohort. All-cause mortality was the secondary outcome. Mean (±SD) age was 53±12 years, 50% were male, and mean serum T₅₀ was 329±58 minutes. A shorter serum T₅₀ is indicative of a higher calcification propensity. Serum T₅₀ was inversely associated with circulating phosphate, age, estimated glomerular filtration rate, and alcohol consumption, whereas plasma magnesium was positively associated with serum T₅₀ (P<0.001, total multivariable model R²=0.281). During median (interquartile range) follow-up for 8.3 (7.8-8.9) years, 364 patients died (5.8%), of whom 95 (26.1%) died from a cardiovascular cause. In multivariable Cox proportional hazard models, each 60 minutes decrease in serum T₅₀ was independently associated with a higher risk of cardiovascular mortality (fully adjusted hazard ratio [95% CI], 1.22 [1.04-1.36], P=0.021). This association was modified by diabetes mellitus; stratified analysis indicated a more pronounced association in individuals with diabetes mellitus.

CONCLUSIONS

Serum T₅₀ is independently associated with an increased risk of cardiovascular mortality in the general population and thus may be an early and potentially modifiable risk marker for cardiovascular mortality.

Effects of erythropoietin on fibroblast growth factor 23 in mice and humans

BACKGROUND

Erythropoietin (EPO) has been reported as a novel determinant of fibroblast growth factor 23 (FGF23) production; however, it is unknown whether FGF23 is stimulated by chronic exposure to EPO or by EPO administration in nonpolycystic chronic kidney disease (CKD) models.

METHODS

We analyzed the effects of chronic EPO on FGF23 in murine models with chronically high EPO levels and normal kidney function. We studied the effects of exogenous EPO on FGF23 in wild-type mice, with and without CKD, injected with EPO. Also, in four independent human CKD cohorts, we evaluated associations between FGF23 and serum EPO levels or exogenous EPO dose.

RESULTS

Mice with high endogenous EPO have elevated circulating total FGF23, increased disproportionately to intact FGF23, suggesting coupling of increased FGF23 production with increased proteolytic cleavage. Similarly, in wild-type mice with and without CKD, a single exogenous EPO dose acutely increases circulating total FGF23 out of proportion to intact FGF23. In these murine models, the bone marrow is shown to be a novel source of EPO-stimulated FGF23 production. In humans, serum EPO levels and recombinant human EPO dose are positively and independently associated with total FGF23 levels across the spectrum of CKD and after kidney transplantation. In our largest cohort of 680 renal transplant recipients, serum EPO levels are associated with total FGF23, but not intact FGF23, consistent with the effects of EPO on FGF23 production and metabolism observed in our murine models.

CONCLUSION

EPO affects FGF23 production and metabolism, which may have important implications for CKD patients.

Dietary Patterns Based on Estimated Glomerular Filtration Rate and Kidney Function Decline in the General Population: The Lifelines Cohort Study

No specific dietary patterns have been established that are linked with loss of kidney function. We aimed to identify an estimated glomerular filtration rate-based dietary pattern (eGFR-DP) and to evaluate its association with eGFR decline and chronic kidney disease (CKD) incidence in the general population. We included 78,335 participants from the Lifelines cohort in the Northern Netherlands. All participants had an eGFR >60 mL/min/1.73 m² at baseline and completed a second visit five years later. The eGFR-DP was constructed at baseline using a 110-item food frequency questionnaire by reduced rank regression, stratified by sex. Logistic regression was performed to evaluated the association between the eGFR-DP score and either a ≥20% eGFR decline or incident CKD. Among women, eGFR-DP were characterized by high consumption of egg, cheese, and legumes and low consumption of sweets, white meat, and commercially prepared dishes. In men, eGFR-DP were characterized by high consumption of cheese, bread, milk, fruits, vegetables, and beer and low consumption of white and red meat. A higher eGFR-DP score was associated with a lower risk of a ≥20% eGFR decline (OR 4th vs. 1st quartile, women: 0.79 [95% CI: 0.73-0.87]; men: 0.67 [0.59-0.76]). The association between the eGFR-DP score and CKD incidence was lost upon adjustment for baseline eGFR. Our results provide support for dietary interventions to prevent kidney function decline in the general population.

Duality of Tocopherol Isoforms and Novel Associations with Vitamins Involved in One-Carbon Metabolism: Results from an Elderly Sample of the LifeLines Cohort Study

Whether the affinity of serum vitamin E with total lipids hampers the appropriate assessment of its association with age-related risk factors has not been investigated in epidemiological studies. We aimed to compare linear regression-derived coefficients of the association of non-indexed and total lipids-indexed vitamin E isoforms with clinical and laboratory characteristics pertaining to the lipid, metabolic syndrome, and one-carbon metabolism biological domains. We studied 1429 elderly subjects (non-vitamin supplement users, 60-75 years old, with low and high socioeconomic status) from the population-based LifeLines Cohort and Biobank Study. We found that the associations of tocopherol isoforms with lipids were inverted in total lipids-indexed analyses, which may be indicative of overcorrection. Irrespective of the methods of standardization, we consistently found positive associations of α-tocopherol with vitamins of the one-carbon metabolism pathway and inverse associations with characteristics related to glucose metabolism. The associations of γ-tocopherol were often opposite to those of α-tocopherol. These data suggest that tocopherol isoforms and one-carbon metabolism are related, with beneficial and adverse associations for α-tocopherol and γ-tocopherol, respectively. Whether tocopherol isoforms, or their interplay, truly affect the one-carbon metabolism pathway remains to be further studied.

A Self-management Approach for Dietary Sodium Restriction in Patients With CKD: A Randomized Controlled Trial

RATIONALE & OBJECTIVE

Patients with chronic kidney disease (CKD) are particularly sensitive to dietary sodium. We evaluated a self-management approach for dietary sodium restriction in patients with CKD.

STUDY DESIGN

Randomized controlled trial.

SETTING & PARTICIPANTS

Nephrology outpatient clinics in 4 Dutch hospitals. 99 adults with CKD stages 1 to 4 or a functioning (estimated glomerular filtration rate≥25mL/min/1.73m²) kidney transplant, hypertension, and sodium intake>130mmol/d.

INTERVENTION

Routine care was compared with routine care plus a web-based self-management intervention including individual e-coaching and group meetings implemented over a 3-month intervention period, followed by e-coaching over a 6-month maintenance period.

OUTCOMES

Primary outcomes were sodium excretion after the 3-month intervention and after the 6-month maintenance period. Secondary outcomes were blood pressure, proteinuria, costs, quality of life, self-management skills, and barriers and facilitators for implementation.

RESULTS

Baseline estimated glomerular filtration rate was 55.0±22.0mL/min/1.73m². During the intervention period, sodium excretion decreased in the intervention group from 188±8 (SE) to 148±8mmol/d (P<0.001), but did not change significantly in the control group. At 3 months, mean sodium excretion was 24.8 (95% CI, 0.1-49.6) mmol/d lower in the intervention group (P=0.049). At 3 months, systolic blood pressure (SBP) decreased in the intervention group from 140±3 to 132±3mm Hg (P<0.001), but was unchanged in the control group. Mean difference in SBP across groups was-4.7 (95% CI, -10.7 to 1.3) mm Hg (P=0.1). During the maintenance phase, sodium excretion increased in the intervention group, but remained lower than at baseline at 160±8mmol/d (P=0.01), while it decreased in the control group from 174±9 at the end of the intervention period to 154±9mmol/d (P=0.001). Consequently, no difference in sodium excretion between groups was observed after the maintenance phase. There was no difference in SBP between groups after the maintenance phase.

LIMITATIONS

Limited power, postrandomization loss to follow-up, Hawthorne effect, lack of dietary data, short-term follow-up.

CONCLUSIONS

A coaching intervention reduced sodium intake at 3 months. Efficacy during the maintenance phase was diminished, possibly due to inadvertent adoption of the intervention by the control group.

FUNDING

Grant funding from the Netherlands Organization for Health Research and Development and the Dutch Kidney Foundation.

TRIAL REGISTRATION

Registered at ClinicalTrials.gov with study number NCT02132013.

Association of Plasma Concentration of Vitamin B12 With All-Cause Mortality in the General Population in the Netherlands

IMPORTANCE

Higher plasma concentrations of vitamin B12 have been associated with mortality in elderly and hospitalized populations, including patients with chronic kidney disease, but the association of plasma concentrations of vitamin B12 with mortality in the general population remains unclear.

OBJECTIVE

To investigate the association of plasma concentrations of vitamin B12 with all-cause mortality.

DESIGN, SETTING, AND PARTICIPANTS

This longitudinal cohort study used post hoc analysis to examine data from participants of the Prevention of Renal and Vascular End-stage Disease Study in Groningen, the Netherlands. Participants included individuals who completed the second screening visit beginning January 1, 2001, excluding those who were missing values of vitamin B12 plasma concentrations or used vitamin B12 supplementation. Follow-up time was defined between the beginning of the second screening round to end of follow-up on January 1, 2011. Data analysis was conducted from October 2, 2018, to February 22, 2019.

EXPOSURES

Plasma vitamin B12 concentration level.

MAIN OUTCOMES AND MEASURES

Death as recorded by the Central Bureau of Statistics of Groningen, the Netherlands.

RESULTS

A total of 5571 participants (mean [SD] age, 53.5 [12.0] years; 2830 [50.8%] men) were included in analyses. Median (interquartile range) plasma concentration of vitamin B12 was 394.42 (310.38-497.42) pg/mL. During the median (interquartile range) of 8.2 (7.7-8.9) years of follow-up, 226 participants (4.1%) died. According to quartiles of the distribution of plasma vitamin B12 concentration levels, mortality rates were 33.8 deaths per 10 000 person-years for the quartile with the lowest plasma concentration of vitamin B12 and 65.7 deaths per 10 000 person-years for the quartile with the highest plasma concentration of vitamin B12. After adjustment for multiple clinical and laboratory variables, Cox regression analyses found a significant association between higher vitamin B12 plasma concentration level and increased risk of all-cause mortality (hazard ratio per 1-SD increase, 1.25 [95% CI, 1.06-1.47]; P = .006).

CONCLUSIONS AND RELEVANCE

These findings suggest that higher levels of plasma concentrations of vitamin B12 were associated with increased risk of all-cause mortality after adjusting for age, sex, renal function, and other clinical and laboratory variables. The mechanisms underlying this association remain to be established.