Obesity has been called a risk factor for chronic kidney disease (CKD), but the evidence for such a conclusion remains unclear. An analysis of the Framingham Offspring Study designed to answer this question suggests that an independent effect of obesity on CKD does not exist. Because this population is primarily white, broad generalization of these findings cannot be made as rates of obesity and CKD are known to vary by race and ethnicity.
Chart Explanation: After adjusting for age and sex, the incidence rate of CKD (estimated glomerular filtration rate (eGFR) < 59 mL/min/1.73 m2 for women; eGFR < 64 mL/min/1.73 m2 for men) is 1.29 times higher (95% CI: 0.93, 1.81) for those who were overweight than for those who were normal weight, and 1.68 times higher (1.10, 2.57) for those who were obese than for those who were normal weight. Further adjustment for diabetes, systolic blood pressure, hypertension treatment, current smoking status, and high-density lipoprotein level at baseline attenuated the association between weight status and CKD. Those who were overweight were 1.06 times higher (95% CI: 0.75, 1.50) than those with normal weight. Those who were obese were 1.09 times higher (95% CI: 0.69, 1.73) than those with normal weight.
The analysis by Foster, et al. examined the Framingham Offspring Study to determine association between body mass index (BMI) and chronic kidney disease (CKD). The Framingham Offspring Study is a longitudinal cohort of the offspring of the original Framingham Heart Study, which comprised a cohort of primarily white men and women from Framingham, Massachusetts, and was designed to study causes of cardiovascular disease. The Framingham Offspring Study cohort, which began in 1971, contains 5,124 participants. Follow-up examinations of this cohort occur every 4 years.
For this analysis, participants who were free of stage 3 CKD at the baseline examination were followed for development of CKD at exams 2 (1978-1981) and 7 (1998-2001). They examined BMI in three different ways, by category (normal, overweight, obese), by quartiles, and as a continuous variable. The relationship between BMI and CKD was determined in the overall population, hypertension-free population, diabetes-free population, and cardiovascular disease-free population.
|Description of Measure||Hazard Ratio of CKD in The Framingham Offspring Study|
|Data Source||Framingham Offspring Study|
|Type of Data Source||Longitudinal cohort study|
|Data Set||Framingham Offspring Study summarized data from published literature|
|Health Care Data System||No|
|Regional or National?||Regional|
|Demographic Group||5,124 children (men and women) and spouses of children of the first Framingham cohort study (Framingham, Massachusetts); primarily white.|
|Numerator||Incident CKD cases|
|Denominator||Cohort members who participated in second and seventh follow-up examinations, who were free of stage 3 CKD at exam 2 and had serum creatinine measurements at exam 7, BMI < 18.5 kg/m2, and no missing covariate data.|
|Definition of CKD||Estimate glomerular filtration rate (eGFR) < 59 mL/min/1.73 m2 for men; eGFR < 64 mL/min/1.73 m2 for women.|
|Glomerular filtration rate||Estimated, Modification of Diet in Renal Disease Study equation: GFR = 186.0 x (serum creatinine)-1.154 x (age)-0.203 x (0.742 if female) x (1.210 if African American).|
|Primary Data Source Indicator||BMI|
|Primary Indicator Method of Measurement||Weight measured by a scale (calibrated with 22.5 kg weight) to the nearest pound while wearing a gown and barefoot. Height measured to nearest 0.25 of an inch |
|Secondary Data Source Indicator||Age and sex (adjustment variables)|
|Secondary (1) Indicator Method of Measurement||Survey|
|Secondary Data Source Indicator||Diabetes, systolic blood pressure, hypertension treatment, current smoking status, and high-density lipoprotein level at baseline (adjustment variables)|
|Secondary (2) Indicator Method of Measurement||Fasting blood sample, survey, and sphygmomanometer|
|Period Currently Available||2001|
|Frequency of Measurement (Primary)||eGFR - Twice (exams 2 and 7); BMI – at baseline|
|U.S. Region Covered by Primary Variable||Offspring of inhabitants of Framingham, Massachusetts|
|Limitations of Indicator||Demographically limited study, primarily white from one region of the United States; Possible over-adjustment for diabetes and hypertension; definition of CKD does not include proteinuria|
|Analytical Considerations||Analysis performed by Framingham Heart Study investigators|