Summary
Background
Metabolic syndrome increases the risk of cardiovascular disease (CVD) and all-cause mortality in the general population.
Aims
To investigate whether metabolic syndrome affects CVD and all-cause mortality in chronic haemodialysis patients.
Methods
This prospective, observational cohort study was carried out at Peking university third hospital from June 2006 to June 2010. Baseline anthropometric and laboratory parameters were evaluated, and causes and times of mortality were documented. Nutritional status of the patients was assessed using subject global assessment (SGA) and serum albumin levels.
Results
Of 162 haemodialysis patients recruited, five were lost to follow-up, leaving 157 in the final cohort, who were followed for 36−42 months. Mean age was 62 ± 11 years and 55.4% were men. Forty-six patients (30%) had metabolic syndrome. In the metabolic syndrome versus the non-metabolic syndrome group, there were fewer patients with malnutrition (by SGA) (15.2% vs. 55.0%; P < 0.001), but there were no significant differences in CVD mortality (8.7% vs. 10.8%; P = 0.9) or all-cause mortality (15.2% vs. 22.5%; P = 0.39), nor in mean observed survival time (30.8 ± 7.3 vs. 29.8 ± 8.5 months; P = 0.49) or total survival time (67 ± 43 vs. 78 ± 48 months; P = 0.20). Cox regression analysis showed that independent mortality risk factors were pre-existing CVD, age more than or equal to 66 years and serum albumin less than 37 g/L (indicating malnutrition).
Conclusion
Metabolic syndrome was associated with a better nutritional status, but not with CVD or all-cause mortality in the haemodialysis patients in this prospective cohort study.
Résumé
Justification
Le syndrome métabolique augmente le risque d’affection cardiovasculaire et de mortalité toute cause dans la population générale.
Objectifs
Évaluer l’hypothèse que le syndrome métabolique pourrait retentir sur le risque cardiovasculaire de la mortalité globale chez des patients en hémodialyse chronique.
Méthode
Cette étude prospective, observationnelle de cohortes a été effectuée dans l’université de Pékin entre juin 2006 et juin 2010. Les caractéristiques anthropométriques et biologiques ont été évaluées ainsi que les causes et les modalités de survenue d’évènements dont la mortalité. Le statut nutritionnel des patients était évalué en utilisant l’échelle SGA ainsi que les concentrations sériques d’albumine.
Résultats
Parmi les 162 patients hémodialysés chroniques inclus, cinq ont été perdus de vue, permettant d’analyser au sein de la cohorte 157 patients, suivis de 36 à 42 mois. L’âge moyen était de 62 ± 11 ans et 55,4 % étaient des patients de sexe masculin. Quarante-six patients (30 %) présentaient un syndrome métabolique. En comparant les groupes avec et sans syndrome métabolique, il y avait un nombre moindre de patients souffrant de malnutrition évalués par SGA (15,2 % vs 55 %, p < 0,001), mais il n’y avait pas de différence significative en ce qui concerne la mortalité cardiovasculaire (8,7 % vs 10,8 %, p = 0,9) ou de mortalité totale (15,2 % vs 22,5 %, p = 0,39). Il n’y avait pas non plus de différence significative en ce qui concerne le délai de survenue (30,8 ± 7,3 vs 29,8 ± 8,5 mois, p = 0,49) ou la durée totale de survie au cours du suivi (67 ± 43 vs 78 ± 48 mois, p = 0,20) au sein de cette cohorte. L’analyse par régression de Cox a montré que les facteurs de risque indépendants de mortalité étaient la présence d’une pathologie cardiovasculaire préexistante, un âge supérieur ou égal à 66 ans et un taux sérique d’albumine inférieur à 37 g/L, synonyme de malnutrition.
Conclusion
Le syndrome métabolique est associé à un meilleur statut nutritionnel, mais pas avec un excès d’évènements cardiovasculaires ou de mortalité totale chez les patients hémodialysés, suivis au sein d’une cohorte prospective.
Introduction
MS, which refers to a group of metabolic risk factors, has been found in recent meta-analyses to increase the risk of incident CVD and all-cause mortality in the general population . Current literature most frequently cites the definitions of MS provided by the NCEP/ATP III and the IDF (2005) .
CVD is the most common cause of hospitalization and death in chronic haemodialysis patients . However, some risk factors for CVD in the general population (e.g. hyperlipidaemia, hypertension and obesity) have been associated with a relatively good prognosis among dialysis patients . This phenomenon is known as reverse epidemiology . We therefore hypothesized that MS may not have a negative effect on mortality; particularly mortality associated with CVD, in haemodialysis patients.
Methods
Patients
Patients were recruited from the haemodialysis centre at Peking university third hospital from June 2006 to December 2007. Patients had to have received haemodialysis for more than or equal to 3 months; patients who started dialysis less than 3 months previously and irregular dialysis patients were not eligible for inclusion. All eligible regular dialysis patients in the centre were included, unless they did not agree to participate in the study. Dialysis lasts 4–5 hours at each session and is conducted three times each week. The ethics committee of Peking university approved the study protocol.
Follow-up and endpoints
Patients were classified based on the presence or absence of MS, and were prospectively followed until June 2010 or until death, if this event occurred earlier. The dates of death were defined as endpoints.
Definitions
The 2006 IDF definition of MS was used: central obesity (waist circumference more than or equal to 80 cm in Asian women or more than or equal to 90 cm in Asian men) plus two of the following factors:
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elevated triglycerides (more than or equal to 1.69 mmol/L) or specific treatment for this lipid abnormality;
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reduced HCL-C (less than 1.03 mmol/L in men or less than 1.29 mmol/L in women) or specific treatment for this lipid abnormality;
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elevated blood pressure (SBP more than or equal to 130 mmHg or DBP more than or equal to 85 mmHg) or treatment for previously diagnosed hypertension;
elevated fasting plasma glucose (more than or equal to 5.55 mmol/L) or a previous diagnosis of type 2 diabetes.
CVD was defined as coronary artery disease, arrhythmia, heart failure, peripheral vascular disease or cerebrovascular disease.
Laboratory and anthropometric variables
Biochemical data were collected at baseline and included haemoglobin, serum creatinine, serum triglycerides, HDL-C, FPG, serum albumin, hs-CRP and serum intact PTH levels. All tests were performed in the central laboratory of our hospital using standard methods. Blood pressure (taken with the patient in the sitting position), height, weight and waist circumference (at umbilical level in a standing position) were recorded. Each patient’s nutritional status was assessed by SGA methods (A = normal nutrition, B = mild malnutrition, C = severe malnutrition) according to the patient’s weight, food intake, symptoms (nausea, vomiting, diarrhoea and constipation), activities and function, disease and its relation to nutritional requirement, metabolic demand and physical findings .
Body composition measurement
Post-dialysis body composition was analysed by Bioelectrical Impedance (BIA, Tanita, Japan). The collected data included body fat (% and kg), lean body mass (kg), muscle mass (kg) and visceral fat rating (1–59 grade; where 1–12 is considered healthy while more than or equal to 13 corresponds to excessive abdominal fat and indicates central obesity). The measurements were performed by skilled staff who were experienced at collecting these measurements.
Statistical analysis
Continuous variables are expressed as the mean ± SD, while frequency variables are expressed as count (%). Continuous variables were compared using one-way analysis of variance or non-parameter testing between the two groups classified by the presence or absence of MS. Frequency variables were compared using the χ 2 test. A Cox regression model was performed to determine risk factors for mortality. The assumption of proportionality was assessed through the analysis of partial residuals of the covariates introduced into the models. Survival between patients with and without MS was compared using Kaplan-Meier analysis and a log-rank test. A P -value < 0.05 was considered statistically significant. All statistical calculations were performed using SPSS 13.0 for Windows.
Results
Baseline characteristics
A total of 162 patients were recruited; five were transferred to other haemodialysis centres, leaving 157 in the final cohort, of whom 99 underwent post-dialysis body composition analysis. Of the 157 patients included, 46 patients (30%) had MS by the IDF criteria . All patients were of Chinese origin. Other baseline characteristics are shown in Table 1 . The dialysis vintage at baseline was significantly shorter among diabetic versus other haemodialysis patients (24 ± 23 vs. 50 ± 49 months, Z = –2.884; P = 0.004).
| All patients ( n = 157) | MS ( n = 46) | Non-MS ( n = 111) | P | |
|---|---|---|---|---|
| Age (years) | 62 ± 11 | 63 ± 10 | 61 ± 13 | 0.45 |
| Men | 87 (55.4) | 22 (47.8) | 65 (58.6) | 0.36 a |
| Primary renal disease | ||||
| Glomerulonephritis | 51 (32.5) | 13 (28.2) | 38 (34.2) | 0.21 a |
| Hypertensive glomerulosclerosis | 40 (25.5) | 12 (26.0) | 28 (24.8) | 0.30 a |
| Diabetes | 30 (19.1) | 12 (26.8) | 18 (16.0) | 0.30 a |
| Other | 36 (22.9) | 9 (19.0) | 27 (25.0) | 0.29 a |
| Dialysis vintage (months) | 44 ± 46 | 36 ± 43 | 47 ± 47 | 0.18 |
| Predialysis SBP (mmHg) | 141 ± 12 | 144 ± 19 | 141 ± 29 | 0.45 |
| BMI (kg/m 2 ) | 24.0 ± 3.7 | 26.2 ± 3.7 | 22.5 ± 3.2 | < 0.001 |
| Body fat (%) b | 27.8 ±10.2 | 33.1 ± 9.3 | 25.0 ± 9.3 | < 0.001 |
| Body fat (kg) b | 18.0 ± 8.3 | 23.4 ± 8.2 | 15.3 ± 6.7 | < 0.001 |
| Lean body mass (kg) b | 46.2 ± 8.4 | 46.8 ± 9.4 | 45.7 ± 7.7 | 0.55 |
| Muscle mass (kg) b | 43.7 ± 8.0 | 44.3 ±9.1 | 43.4 ±7.9 | 0.90 |
| Visceral fat rating (grade) b | 11.1 ± 4.3 | 13.5 ± 4.6 | 9.7 ± 3.6 | < 0.001 |
| Waist circumference (cm) | 86 ± 8 | 90 ± 8 | 83 ± 6 | < 0.001 |
| Malnutrition (B, assessed by SGA) | 48 (43.3) | 7 (15.2) | 61 (55.0) | < 0.001 a |
| Haemoglobin (g/L) | 111 ± 15 | 116 ± 10 | 109 ± 16 | 0.02 |
| Serum albumin (g/L) | 40.0 ± 2.9 | 41.0 ± 1.8 | 40.0 ± 3.1 | 0.01 |
| Triglycerides (mmol/L) | 2.1 ± 1.4 | 2.8 ± 1.5 | 1.8 ± 1.2 | 0.001 |
| HDL-C (mmol/L) | 1.3 ± 0.5 | 1.1 ± 0.4 | 1.3 ± 0.6 | 0.013 |
| Total cholesterol (mmol/L) | 4.2 ± 0.8 | 4.6 ± 0.7 | 4.1 ± 0.7 | < 0.001 |
| Fasting glucose (mmol/L) | 5.4 ± 0.3 | 6.1 ± 0.4 | 5.1 ± 0.3 | 0.017 |
| PTH (pg/mL) | 256 ± 423 | 263 ± 443 | 273 ± 447 | 0.22 |
| URR (%) | 66.9 ± 7.0 | 67.3 ± 7.0 | 66.0 ± 7.8 | 0.20 |
| hs-CRP (mg/L) | 6.02 ± 25 | 3.0 ± 4.2 | 7.1± 29.2 | 0.092 |
| Hypertension | 108 (68.8) | 32 (69.6) | 76 (68.5) | 0.89 a |
| Hypertriglyceridaemia | 70 (44.6) | 29 (63.0) | 41 (36.9) | 0.002 a |
| Pre-existing CVD | 50 (31.8) | 13 (28.3) | 37 (33.3) | 0.85 a |
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