Sodium distribution in black and white women.

Delayed gamma neutron activation analysis (DGNA) was performed on 99 black and 168 healthy white women, aged 20-80 years, to examine sodium distribution in the two ethnic groups. Elements measured included total body levels of sodium (TBNa) and chlorine (TBCl). The black women were heavier, and consequently had a higher body surface area. Sodium excess (Naes) was calculated from TBNa and TBCl. Total body water was measured by tritiated water dilution. TBNa was higher in black than white women, and this difference persisted when the values were corrected for body surface area. TBNa and Naes declined significantly with age in white women, whereas extracellular fluid sodium (ECFNa) remained constant. The change with age was not statistically significant in black women for TBNa, Naes or ECFNa. Our sample of healthy black women had a higher TBNa and Naes than healthy white women. This difference persisted after adjustment for body surface area, so that values for sodium distribution need to be adjusted for race. The change in TBNa with age in white women appears to be due to their decline of skeletal tissue mass with a consequent decline in nonexchangeable sodium.