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The relation between sodium intake and cardiovascular disease is controversial. This study used individual-participant data from six prospective cohorts of healthy adults. Higher sodium and lower potassium intakes, estimated from multiple 24-hour urine samples, were associated in a dose-dependent manner with a higher cardiovascular risk.

Key Points Physical inactivity is a major modifiable risk factor for poor health-related quality of life, morbidity and mortality in patients with renal disease An urgent need exists for the better assessment and management of physical inactivity in patients with renal disease The level of physical activity in patients with chronic kidney disease (CKD) commonly decreases with disease progression, and does not fully recover after transplantation Regular physical activity is beneficial across all stages of CKD, improving cardiometabolic, neuromuscular, and cognitive function, and can reduce the comorbidity burden in patients with renal disease Physical activity, together with nutrition, is now recognized as an important component in the management of patients with CKD; a behavioural approach is crucial to help patients successfully adopt and maintain improved physical activity habits Regular physical activity is associated with reduced mortality in the general population and in patients with chronic kidney disease. Here, the authors discuss the importance of physical activity for patients with renal disease and patient-reported barriers and facilitators for physical activity. Regular physical activity is associated with an increased quality of life and reduced morbidity and mortality in the general population and in patients with chronic kidney disease (CKD). Physical activity, cardiorespiratory fitness, and muscle mass decrease even in the early stages of CKD, and continue to decrease with disease progression; notably, full recovery is generally not achieved with transplantation. The combined effects of uraemia and physical inactivity drive the loss of muscle mass. Regular physical activity benefits cardiometabolic, neuromuscular and cognitive function across all stages of CKD, and therefore provides an approach to address the multimorbidity of the CKD population. Interestingly, maintenance of muscle health is associated with renoprotective effects. Despite evidence of its benefits, physical activity and exercise management are not routinely addressed in the care of these patients. Although studies defining the optimum frequency, duration and intensity of physical activity are lacking, evidence from related fields can guide practical approaches to the care of patients with renal disease. Optimization of metabolic and nutritional status alongside promotion of physical activity is recommended. Behavioural approaches are now recognized as crucial in helping patients to adopt lifestyle changes and might prove valuable in integrating physical activity into renal care.

Background Creatinine is the most widely used test to estimate the glomerular filtration rate (GFR), but muscle mass as key determinant of creatinine next to renal function may confound such estimates. We explored effects of 24‐h height‐indexed creatinine excretion rate (CER index) on GFR estimated with creatinine (eGFRCr), muscle mass‐independent cystatin C (eGFRCys), and the combination of creatinine and cystatin C (eGFRCr‐Cys) and predicted probabilities of discordant classification given age, sex, and CER index. Methods We included 8076 adults enrolled in the PREVEND study. Discordant classification was defined as not having eGFRCr <60 mL/min per 1.73 m2 when eGFRCys was <60 mL/min/1.73 m2. Baseline effects of age and sex on CER index were quantified with linear models using generalized least squares. Baseline effects of CER index on eGFR were quantified with quantile regression and logistic regression. Effects of annual changes in CER index on trajectories of eGFR were quantified with linear mixed‐effects models. Missing observations in covariates were multiply imputed. Results Mean (SD) CER index was 8.0 (1.7) and 6.1 (1.3) mmol/24 h per meter in male and female participants, respectively (Pdifference < 0.001). In male participants, baseline CER index increased until 45 years of age followed by a gradual decrease, whereas a gradual decrease across the entire range of age was observed in female participants. For a 70‐year‐old male participant with low muscle mass (CER index of 2 mmol/24 h per meter), predicted baseline eGFRCr and eGFRCys disagreed by 24.7 mL/min/1.73 m2 (and 30.1 mL/min/1.73 m2 when creatinine was not corrected for race). Percentages (95% CI) of discordant classification in male and female participants aged 60 years and older with low muscle mass were 18.5% (14.8–22.1%) and 15.2% (11.4–18.5%), respectively. For a 70‐year‐old male participant who lost muscle during follow‐up, eGFRCr and eGFRCys disagreed by 1.5, 5.0, 8.5, and 12.0 mL/min/1.73 m2 (and 6.7, 10.7, 13.5, and 15.9 mL/min/1.73 m2 when creatinine was not corrected for race) at baseline, 5 years, 10 years, and 15 years of follow‐up, respectively. Conclusions Low muscle mass may cause considerable overestimation of single measurements of eGFRCr. Muscle wasting may cause spurious overestimation of repeatedly measured eGFRCr. Implementing muscle mass‐independent markers for estimating renal function, like cystatin C as superior alternative to creatinine, is crucial to accurately assess renal function in settings of low muscle mass or muscle wasting. This would also eliminate the negative consequences of current race‐based approaches.

Background Loss of muscle mass is linked with impaired quality of life and an increased risk of morbidity and premature mortality. Iron is essential for cellular processes such as energy metabolism, nucleotide synthesis and numerous enzymatic reactions. As the effects of iron deficiency (ID) on muscle mass and function are largely unknown, we aimed to assess the relation between ID and muscle mass in a large population‐based cohort, and subsequently studied effects of ID on cultured skeletal myoblasts and differentiated myocytes. Methods In a population‐based cohort of 8592 adults, iron status was assessed by plasma ferritin and transferrin saturation, and muscle mass was estimated using 24‐h urinary creatinine excretion rate (CER). The relationships of ferritin and transferrin saturation with CER were assessed by multivariable logistic regression. Furthermore, mouse C2C12 skeletal myoblasts and differentiated myocytes were subjected to deferoxamine with or without ferric citrate. Myoblast proliferation was measured with a colorimetric 5‐bromo‐2′‐deoxy‐uridine ELISA assay. Myocyte differentiation was assessed using Myh7‐stainings. Myocyte energy metabolism, oxygen consumption rate and extracellular acidification rate were assessed using Seahorse mitochondrial flux analysis, and apoptosis rate with fluorescence‐activated cell sorting. RNA sequencing (RNAseq) was used to identify ID‐related gene and pathway enrichment in myoblasts and myocytes. Results Participants in the lowest age‐ and sex‐specific quintile of plasma ferritin (OR vs middle quintile 1.62, 95% CI 1.25–2.10, P < 0.001) or transferrin saturation (OR 1.34, 95% CI 1.03–1.75, P = 0.03) had a significantly higher risk of being in the lowest age‐ and sex‐specific quintile of CER, independent of body mass index, estimated GFR, haemoglobin, hs‐CRP, urinary urea excretion, alcohol consumption and smoking status. In C2C12 myoblasts, deferoxamine‐induced ID reduced myoblast proliferation rate (P‐trend <0.001) but did not affect differentiation. In myocytes, deferoxamine reduced myoglobin protein expression (−52%, P < 0.001) and tended to reduce mitochondrial oxygen consumption capacity (−28%, P = 0.10). Deferoxamine induced gene expression of cellular atrophy markers Trim63 (+20%, P = 0.002) and Fbxo32 (+27%, P = 0.048), which was reversed by ferric citrate (−31%, P = 0.04 and −26%, P = 0.004, respectively). RNAseq indicated that both in myoblasts and myocytes, ID predominantly affected genes involved in glycolytic energy metabolism, cell cycle regulation and apoptosis; co‐treatment with ferric citrate reversed these effects. Conclusions In population‐dwelling individuals, ID is related to lower muscle mass, independent of haemoglobin levels and potential confounders. ID impaired myoblast proliferation and aerobic glycolytic capacity, and induced markers of myocyte atrophy and apoptosis. These findings suggest that ID contributes to loss of muscle mass.

Background Serum creatinine is used as initial test to derive eGFR and confirmatory testing with serum cystatin C is recommended when creatinine‐based eGFR is considered less accurate due to deviant muscle mass. Low muscle mass is associated with increased risk of premature mortality. However, the associations of serum creatinine and cystatin C with muscle mass and mortality remain unclear and require further investigation to better inform clinical decision‐making. Methods We included 8437 community‐dwelling adults enrolled in the Dutch PREVEND study and 5033 in the US NHANES replication cohort. Associations of serum creatinine and/or cystatin C with muscle mass surrogates and mortality were quantified with linear and Cox proportional hazards regression, respectively. Missing observations in covariates were multiply imputed using Substantive Model Compatible Fully Conditional Specification. Results Mean (SD) age of PREVEND and NHANES participants (50% and 48% male) were 49.8 (12.6) and 48.7 (18.7) years, respectively. Median (Q1–Q3) serum creatinine and cystatin C were 71 (61–80) and 80 (62–88) μmol/L and 0.87 (0.78–0.98) and 0.91 (0.80–1.10) mg/L, respectively. Higher serum creatinine was associated with greater muscle mass, while serum cystatin C was not associated with muscle mass. Adjusting both markers for each other strengthened the positive relationship between serum creatinine and muscle mass and revealed an inverse association between serum cystatin C and muscle mass. In the PREVEND cohort, 1636 (19%) deaths were registered over a median follow‐up of 12.9 (5.8–16.3) years with a 10‐year mortality rate (95% CI) of 7.6% (7.1–8.2%). In the NHANES, 1273 (25%) deaths were registered over a median follow‐up of 17.9 (17.3–18.5) years with a 10‐year mortality rate of 13.8% (12.8–14.7%). Both markers were associated with increased mortality. Notably, when adjusted for each other, higher serum creatinine was associated with decreased mortality, while the association between serum cystatin C and increased mortality strengthened. The shapes of the associations in the PREVEND study and NHANES were almost identical. Conclusions The strong association between serum creatinine and muscle mass challenges its reliability as GFR marker, necessitating a more cautious approach in its clinical use. The minimal association between serum cystatin C and muscle mass supports its increased use as a more reliable alternative in routine clinical practice.

Background Low physical activity and reduced physical functioning are common after renal transplantation, resulting in a reduced quality of life. Another common post-transplantation complication is poor cardio-metabolic health, which plays a main role in long-term outcomes in renal transplant recipients (RTR). It is increasingly recognized that weight gain in the first year after transplantation, especially an increase in fat mass, is a highly common contributor to cardio-metabolic risk. The aim of this study is to compare the outcomes of usual care to the effects of exercise alone, and exercise combined with dietary counseling, on physical functioning, quality of life and post-transplantation weight gain in RTR. Methods The Active Care after Transplantation study is a multicenter randomized controlled trial with three arms in which RTR from 3 Dutch hospitals are randomized within the first year after transplantation to usual care, to exercise intervention (3 months supervised exercise 2 times per week followed by 12 months active follow-up), or to an exercise + diet intervention, consisting of the exercise training with additional dietary counseling (12 sessions over 15 months by a renal dietician). In total, 219 participants (73 per group) will be recruited. The primary outcome is the subdomain physical functioning of quality of life, (SF-36 PF). Secondary outcomes include other evaluations of quality of life (SF-36, KDQOL-SF, EQ-5D), objective measures of physical functioning (aerobic capacity and muscle strength), level of physical activity, gain in adiposity (body fat percentage by bio-electrical impedance assessment, BMI, waist circumference), and cardiometabolic risk factors (blood pressure, lipids, glucose metabolism). Furthermore, data on renal function, medical history, medication, psychological factors (motivation, kinesiophobia, coping style), nutrition knowledge, nutrition intake, nutrition status, fatigue, work participation, process evaluation and cost-effectiveness are collected. Discussion Evidence on the effectiveness of an exercise intervention, or an exercise + diet intervention on physical functioning, weight gain and cardiometabolic health in RTR is currently lacking. The outcomes of the present study may help to guide future evidence-based lifestyle care after renal transplantation. Trial registration Number: NCT01047410 .

Cigarette smoking continues to be one of the major risk factors for increased morbidity and mortality worldwide. Among many adverse health effects, smoking can induce erythrocytosis, which is commonly believed to result from elevated serum erythropoietin (EPO) levels. Currently, however, this notion is only alleged, without data available to substantiate it. Hence, we analyzed data from the Prevention of Renal and Vascular End-Stage Disease study, a prospective population-based cohort study. Smoking behavior was quantified as number of cigarettes smoked per day and as 24-hour urinary cotinine excretion levels, an objective and quantitative measure of nicotine exposure. In 6808 community-dwelling participants, the prevalence of nonsmokers, former smokers, and current smokers were 29%, 43%, and 28%, respectively. Hematocrit levels were higher in current smokers (41.4%±3.6%) than in nonsmokers (40.3%±3.6%) (P<.001). In contrast, median EPO levels were lower in current smokers (7.5 IU/L; interquartile range [IQR], 5.7-9.6 IU/L) than in nonsmokers (7.9 IU/L; IQR, 6.0-10.7 IU/L) (P<.001). In multivariate linear regression analysis, current smoking, compared with nonsmoking, was independently positively associated with hematocrit levels (β=.12; P<.001) and hemoglobin levels (β=.11; P<.001), but inversely associated with EPO levels (β=−.09; P<.001). In sensitivity analyses, we observed a dose-dependent inverse association of smoking exposure reflected by 24-hour urinary cotinine excretion levels with EPO levels. Contrary to common belief, we identified that in the general population, smoking is inversely associated with EPO levels. Future mechanistic insight is needed to unravel the currently identified association, and if reproduced in other studies, guidelines for diagnosis of secondary erythrocytosis may need to be revisited.

Background Muscle mass, as determined from 24‐h urinary creatinine excretion rate (CER), is an independent predictor for mortality and graft failure in renal transplant recipients (RTR). It is currently unknown whether CER is comparable with healthy controls after transplantation and whether it reflects muscle performance besides muscle mass. We aimed to compare urinary CER and muscle performance between RTR and healthy controls and to investigate whether urinary CER is associated with muscle performance in RTR. Methods We included RTR, transplanted between 1975 and 2016 in the University Medical Center Groningen. Healthy controls were subjects screened for kidney donation. CER was calculated from a 24‐h urine collection. Muscle performance was assessed by handgrip strength, sit‐to‐stand test, and 2‐min walk test. Statistical analyses were performed using linear regression analyses. Results We included 184 RTR (mean age 56.9 ± 11.9 years, 54% male recipient) and 78 healthy controls (age 57.9 ± 9.9, 47% male recipient). RTR were at a median time of 4.0 (1.1–8.8) years after transplantation. Mean CER was lower in RTR compared to healthy controls (11.7 ± 4.0 vs. 13.1 ± 5.2 mmol/24 h; P = 0.04). Significantly poorer results in muscle performance were found in RTR compared to controls for the handgrip strength (30.5 [23.7–41.1] N vs. 38.3 [29.3–46.0] N, P < 0.001) and the 2‐min walk test (151.5 ± 49.2 m vs. 172.3 ± 12.2 m, P < 0.001) but not for the sit‐to‐stand (12.2 ± 3.3 m vs. 11.9 ± 2.8 m, P = 0.46). In RTR, CER was significantly associated with handgrip strength (std. β 0.33; P < 0.001), independent of adjustment for potential confounders. In RTR, CER was neither associated with the time used for the sit‐to‐stand test (std. β −0.09; P = 0.27) nor with the distance covered during the 2‐min walk test (std. β 0.07; P = 0.40). Conclusions Muscle mass as measured by CER in RTR is lower compared to controls. CER is positively associated with muscle performance in RTR. The results demonstrate that CER does not only reflect muscle mass but also muscle performance in this patient setting. Determination of CER could be an interesting addition to the imaging technique armamentarium available and applied for evaluation of muscle mass in clinical intervention studies and observational studies.

The creatinine excretion rate (CER) is inversely associated with mortality in the general and renal transplant population. The CER is a marker for muscle mass. It is unknown whether the CER is associated with outcome in diabetes. We therefore investigated whether the CER is a determinant of all-cause mortality in diabetic patients. We used data from the combined Reduction of Endpoints in Non-insulin dependent diabetes mellitus with the Angiotensin II Antagonist Losartan (RENAAL) and Irbesartan Diabetic Nephropathy Trial (IDNT) studies. A total of 1,872 patients (58% of the overall population) with type 2 diabetes and nephropathy with valid 24-h urinary creatinine excretion data were included. The primary end point of the analyses was all-cause mortality. Mean age was 60 ± 8 years and median CER was 1,407 (total range 400-3,406) mg/day. Body surface area, hemoglobin, black race, and albuminuria were positive independent determinants of the CER, whereas female sex and age were inverse independent determinants of the CER. During a median follow-up of 36 (29-45) months, 300 patients died. In a Kaplan-Meier analysis of sex-stratified tertiles of the CER, risk for all-cause mortality increased with decreasing CER (P < 0.001). In a multivariable Cox regression analysis, lower CER (as a continuous variable) was independently associated with increased risk for all-cause mortality (hazard ratio 0.39 [95% CI 0.29-0.52], P < 0.001). Adjustment for potential collection errors did not materially change these associations. Lower CER was strongly associated with increased all-cause mortality in patients with type 2 diabetes and nephropathy. As the CER can be considered a proxy for muscle mass, this puts renewed emphasis on physical condition and exercise in this population.

Sarcopenia is a progressive skeletal muscle disorder, which is characterized by low muscle mass and strength and associated with increased risk of adverse outcomes, including premature death. 1 Despite improved awareness of the importance of sarcopenia by health care professionals, fundamental findings from research lack translation to clinical practice—a gap that must be bridged given the major personal, social, and economic burdens ensued by its presence. 1 We report on a renal transplant recipient who experienced substantial muscle wasting during 27.5 years of follow‐up. Body mass index—defined as weight divided by height in metres squared—is considered the ‘gold standard’ measure of weight and hence abundantly used in clinical decision making and research. In 1985, however, Andres and colleagues called this concept into question by demonstrating that the association between height‐adjusted weight and mortality follows a U‐shaped curve. [...]the nadir of that curve (i.e. the weight at which mortality rates were lowest) was highly dependent on age. 3 These findings gave rise to a concept referred to as the ‘obesity paradox’, which still receives much attention. 4 We built on this concept with the patient's gradual, yet inexorable, wasting of muscle mass as harbinger of deteriorating clinical condition and, eventually, death—all in absence of declining BMI.