31 There is a continuous positive association between baseline BMI and risk of future diabetes, which is stronger in Asians than Caucasian cohorts.32 In the Nurses Health study,33 for each 5-unit increase in BMI, the adjusted relative risk of incident diabetes
in Asians was 2.36 (95% CI: 1.83–3.04) and for Caucasians was 1.96 (95% CI: 1.93–2.00). The impact of weight gain from baseline was also a significant factor; in Asians, each 5 kg weight gain was associated with an increase in risk of incident diabetes by 84% (95% CI: 58–114) and 37% (95% CI: 35–38) in Caucasians. There are several mechanisms by which obesity may be expected to have a detrimental effect on the kidney. Obesity increases single-nephron mTOR inhibitor glomerular filtration rate (GFR), increases activation of the sympathetic nervous and renin-angiotensin systems, promotes
salt resorption in the proximal tubule34 and has been associated with specific histological changes including glomerulomegaly and focal segmental sclerosing lesions.35 Obesity is associated click here with and often precedes multiple factors associated with development of kidney dysfunction – hypertension, diabetes and atherosclerosis but data from longitudinal cohort studies suggest that obesity may also be an independent risk factor for the development of CKD and ESKD36–41 (see Table 2). Analysis of the Kaiser Permanente cohort40 demonstrated that there is a progressive increase
in risk of ESKD associated with obesity, independent of age, gender, race, smoking, previous myocardial infarct, baseline cholesterol, proteinuria and serum creatinine. Compared with normal BMI, the adjusted relative risk for ESKD was 1.87 for overweight and 3.57 for BMI between 30 and 34.9 kg/m2 and 6.12 for BMI between 34 and 39.9 kg/m2 and 7.07 for BMI > 40 kg/m2. Adjustment for baseline BP and presence of diabetes attenuated the risk slightly but the associations remained strong. It is important to note that while there is a fairly consistent increase in relative risk between obesity and kidney disease, the absolute risk of ESKD for an individual is small. Using the Kaiser Permanente from population as an example, the adjusted rate of ESKD is 10 per 100 000 person years for normal BMI and 46 per 100 000 person years for BMI 30–34.9 kg/m2. In terms that patients are more likely to comprehend, this equates to a risk of ESKD over 10 years of 1 in every 1000 normal BMI patients, compared with 4.6 in every 1000 obese patients. The associations between obesity and incident CKD, are to a variable degree dependent on the associated comorbidities of hypertension and diabetes. This is of relevance when assessing donors who have been carefully screened for these risk factors, and the risk associated with obesity in the absence of these is likely to be small.