Association between obesity and kidney disease: a systematic review and meta-analysis

Early histological changes in the kidney of people with morbid obesity

BACKGROUND

Morbid obesity represents a major health problem with increasing incidence worldwide. The clinical manifestation of renal involvement in obesity is proteinuria, and the histological feature is glomerulomegaly with or without focal and segmental glomerulosclerosis (FSGS). In this study, we have investigated the very early histological changes in kidneys of people with morbid obesity and no proteinuria. Patients and methods. Eighteen patients with body mass index (BMI) >50 kg/m(2) who underwent a variant of biliopancreatic diversion with Roux-en-Y reconstruction (BPD-RYGBP) and consented to undergo a renal biopsy during the surgical procedure were included in the study. The estimation of early histological changes was performed on light (n = 18) and electron microscopy (n = 13).

RESULTS

The mean glomerular cross-sectional area was 30 943 +/- 10,984 microm(2) that is higher than that observed in non-obese individuals. In 21% of the examined glomeruli, the glomerular planar surface area (GPSA) was >40,000 microm(2). Thickening of the glomerular basement membrane (GBM) and scattered paramesangial deposits were identified in 9 of 13 patients (70%) whose renal tissue was examined by electron microscopy. A reduction in the slit pore frequency was observed in obese patients due to extensive foot process effacement. Significant positive correlations between mean GPSA and body weight (r = 0.462, P = 0.05), and between GBM thickness and HbA1c, serum total cholesterol and triglyceride levels (r = 0.60, P = 0.05; r = 0.789, P = 0.004; r = 0.70, P = 0.016, respectively), were observed.

CONCLUSIONS

Glomerulomegaly as well as histological lesions resembling those of early diabetic nephropathy are observed in kidney biopsies of patients with morbid obesity even before the appearance of microalbuminuria. The potential regression of these changes after weight loss needs to be clarified.

Obesity and impaired renal function: potential for lifestyle intervention?

Obesity is recently acknowledged as an important independent risk factor for kidney disease, in which epidemiological evidence played a crucial role. This risk is probably explained by intracellular lipid accumulation in the kidney. Lifestyle factors such as physical activity and diet play a role in the development of kidney disease in several stages: development of obesity and the metabolic syndrome, occurrence of obesity-related glomerulopathy, improvement of hemodialysis patients, and prevention of graft dysfunction and graft loss after renal transplantation. After the recent success of lifestyle intervention to prevent diabetes, further research is needed to show the effects of lifestyle changes to prevent and reduce obesity-related morbidity, including chronic kidney disease.

Body-mass index and cause-specific mortality in 900 000 adults: collaborative analyses of 57 prospective studies

BACKGROUND

The main associations of body-mass index (BMI) with overall and cause-specific mortality can best be assessed by long-term prospective follow-up of large numbers of people. The Prospective Studies Collaboration aimed to investigate these associations by sharing data from many studies.

METHODS

Collaborative analyses were undertaken of baseline BMI versus mortality in 57 prospective studies with 894 576 participants, mostly in western Europe and North America (61% [n=541 452] male, mean recruitment age 46 [SD 11] years, median recruitment year 1979 [IQR 1975-85], mean BMI 25 [SD 4] kg/m(2)). The analyses were adjusted for age, sex, smoking status, and study. To limit reverse causality, the first 5 years of follow-up were excluded, leaving 66 552 deaths of known cause during a mean of 8 (SD 6) further years of follow-up (mean age at death 67 [SD 10] years): 30 416 vascular; 2070 diabetic, renal or hepatic; 22 592 neoplastic; 3770 respiratory; 7704 other.

FINDINGS

In both sexes, mortality was lowest at about 22.5-25 kg/m(2). Above this range, positive associations were recorded for several specific causes and inverse associations for none, the absolute excess risks for higher BMI and smoking were roughly additive, and each 5 kg/m(2) higher BMI was on average associated with about 30% higher overall mortality (hazard ratio per 5 kg/m(2) [HR] 1.29 [95% CI 1.27-1.32]): 40% for vascular mortality (HR 1.41 [1.37-1.45]); 60-120% for diabetic, renal, and hepatic mortality (HRs 2.16 [1.89-2.46], 1.59 [1.27-1.99], and 1.82 [1.59-2.09], respectively); 10% for neoplastic mortality (HR 1.10 [1.06-1.15]); and 20% for respiratory and for all other mortality (HRs 1.20 [1.07-1.34] and 1.20 [1.16-1.25], respectively). Below the range 22.5-25 kg/m(2), BMI was associated inversely with overall mortality, mainly because of strong inverse associations with respiratory disease and lung cancer. These inverse associations were much stronger for smokers than for non-smokers, despite cigarette consumption per smoker varying little with BMI.

INTERPRETATION

Although other anthropometric measures (eg, waist circumference, waist-to-hip ratio) could well add extra information to BMI, and BMI to them, BMI is in itself a strong predictor of overall mortality both above and below the apparent optimum of about 22.5-25 kg/m(2). The progressive excess mortality above this range is due mainly to vascular disease and is probably largely causal. At 30-35 kg/m(2), median survival is reduced by 2-4 years; at 40-45 kg/m(2), it is reduced by 8-10 years (which is comparable with the effects of smoking). The definite excess mortality below 22.5 kg/m(2) is due mainly to smoking-related diseases, and is not fully explained.

Obesity management in adults with CKD

A 22-year-old African-American woman who has been dialysis dependent for four months due to hypertensive kidney disease is referred for kidney transplantation evaluation. Due to the recent occlusion of her left forearm arteriovenous graft, she is currently being dialyzed via a right internal jugular tunneled catheter. Her medications include methyldopa 250 mg bid, Tums 1000 mg with each meal and erythropoietin with dialysis. The patient is single without children, unemployed and lives with her 38 year old mother. She does not smoke or drink. Her review of systems is unremarkable. On physical exam, her weight is 284 pounds, height is 5 feet 2 inches and her body mass index is 51.9 kg/m2. The blood pressure is 130/80 and the cardiac and pulmonary exams are unremarkable. The surgeon feels she is otherwise a good candidate for transplantation except she must lose weight before being listed. What advice should she be given regarding weight loss?

Health outcomes for living kidney donors with isolated medical abnormalities: a systematic review

Individuals with isolated medical abnormalities (IMAs) are undergoing living donor nephrectomy more frequently. Knowledge of health risks for these living donors is important for donor selection, informed consent and follow-up. We systematically reviewed studies with > or = 3 living kidney donors with preexisting IMAs, including older age, obesity, hypertension, reduced glomerular filtration rate (GFR), proteinuria, microscopic hematuria and nephrolithiasis. We abstracted data on study and donor characteristics, perioperative outcomes, longer term renal and blood pressure outcomes and mortality and compared them to those of non-IMA donors. We found 22 studies on older donors (n = 987), 10 on obese donors (n = 484), 6 on hypertensive donors (n = 125), 4 on donors with nephrolithiasis (n = 32), 2 on donors with microscopic hematuria and one study each on donors with proteinuria or reduced GFR. Perioperative outcomes for donors with and without IMAs were similar. Few studies reported longer term (> or = 1 year) rates of hypertension, proteinuria or renal function. Studies were frequently retrospective and without a comparison group. Given the variability among studies and their methodological limitations, uncertainties remain regarding long-term medical outcomes for IMA donors. As transplant centers continue to cautiously screen and counsel potential IMA donors, rigorously conducted, longer term prospective cohort studies are needed.

Supersized kidneys: Lessons from the preclinical obese kidney

The worldwide prevalence of obesity continues to rise. Obesity has been shown to increase the risk of both the development and the progression of renal failure, even after correction for other comorbid conditions. The ability of nephrologists to intervene will require greater understanding of obesity's renal physiologic effects. Kidney biopsies and functional studies performed on morbidly obese patients without overt renal disease who presented for bariatric surgery have helped to elucidate the earliest obesity-related structural and functional responses.