Rise in Extracellular Fluid Volume During High Sodium Depends on BMI in Healthy Men

Abstract

A high sodium (HS) intake is associated to increased cardiovascular and renal risk, especially in overweight subjects. We hypothesized that abnormal sodium and fluid handling is involved, independent of hypertension or insulin resistance. Therefore, we studied the relation between BMI and sodium‐induced changes in extracellular fluid volume (ECFV; distribution volume of 125I‐iothalamate) in 78 healthy men, not selected for BMI. A total of 78 subjects with a median BMI of 22.5 (range: 19.2–33.9 kg/m2) were studied after 1 week on a low sodium (LS) diet (50 mmol Na+/d) and after 1 week on HS (200 mmol Na+/d). The change from LS to HS resulted in an increase in ECFV of 1.2 ± 1.8 l. Individual changes in ECFV were correlated to BMI (r = 0.361, P < 0.01). Furthermore, in response to HS, a higher BMI was associated to a higher rise in filtered load of sodium (FLNa+ = [Na+] × GFR, r = 0.281, P < 0.05). Thus, a shift to HS leads to a larger rise in ECFV in healthy subjects with higher BMI, associated with an elevated FLNa+ during HS. Although no hypertension occurred in these healthy subjects, our data provide a potential explanation for the interaction of sodium intake and BMI on cardiovascular and renal risk. Exaggerated fluid retention may be an early pathogenic factor in the cardiorenal complications of overweight.

Use of Body Surface Area for Assessing Extracellular Fluid Volume and Glomerular Filtration Rate in Obesity

“…Brochner-Mortensen et al [5] matched obese and non-obese patients for height and age and found higher ECV in the obese, while Visser et al [20] recorded a positive correlation between BMI and the increase in ECV in response to a high sodium diet. One might expect these results, however, as they ignore the contribution to BMI of lean tissues and the fact that BMI bears a strong positive correlation with BSA (fig.…”

Modification of Diet in Renal Disease versus Chronic Kidney Disease Epidemiology Collaboration equation to estimate glomerular filtration rate in obese patients

“…We rather think that this overestimation of mGFR results from an exaggerated correction of the distribution volume of creatinine when indexing with BSA. At this point, we remind readers that some authors have suggested that GFR should be indexed against extracellular volume rather than BSA, and it has actually been shown that a high sodium intake increased GFR but not GFR indexed to extracellular volume [53][54][55]. Moreover, it is interesting to note that the percentage of patients (including in non-CKD obese subjects) with indexed mGFR defining hyperfiltration was extremely low in our study, whereas hyperfiltration is a well-described functional and histological entity in obese subjects [14,47,56,57].…”

Central Body Fat Distribution Associates with Unfavorable Renal Hemodynamics Independent of Body Mass Index

“…[14][15][16][17] To account for such bias, height normalization has been recommended, 14 as well as normalization to extracellular volume. 18,19 However, there is no validated gold standard. Unfortunately, data on extracellular volume were available in only a relatively small subset of persons in this study.…”