TABLE 2.
Urinary sodium excretion (mg/24 h) by decade1
| Group | 1957–20032 | Before 1980 | 1981–1990 | 1991–2000 | After 2000 | P for trend3 |
| All groups | 3526 (38) | 3319 (8) | 3418 (10) | 3499 (14) | 3849 (6) | 0.14 |
| Age | ||||||
| <50 y | 3616 (21) | 3356 (5) | 3758 (6) | 3548 (8) | 3792 (2) | 0.73 |
| ≥50 y | 3369 (13) | — | 2975 (3) | 3420 (6) | 3978 (4) | 0.02 |
| Sex | ||||||
| Male | 3911 (13) | 3868 (2) | 3548 (3) | 4052 (6) | 4149 (2) | 0.30 |
| Female | 3084 (12) | 2921 (1) | 2577 (2) | 3203 (7) | 3242 (2) | 0.16 |
| Race | ||||||
| Black or African American | 3645 (9) | 3021 (2) | 4048 (1) | 3618 (4) | 3889 (2) | 0.22 |
| White | 3801 (11) | 3519 (1) | 4232 (1) | 3755 (7) | 4024 (2) | 0.81 |
All values are means; number of studies in parentheses. For estimation of values of all groups, each study was weighted by the square root of the number of participants; for analysis of demographic subgroups, each study was weighted by the square root of the number of subgroup participants (eg, the number of blacks or whites in each study); 4 studies [ie, INTERSALT (International Cooperative Study on the Relation of Blood Pressure to Electrolyte Excretion in Populations) (48, 49), Schachter (55), Gros et al (59), and Veverbrants and Arky (60)] did not provide precise ages of study participants.
Difference in values between subgroups: <50 compared with ≥50 y (P = 0.002, ANOVA), men compared with women (P < 0.001, ANOVA), and blacks or African Americans compared with whites (P = 0.90, ANOVA).
Calculated with weighted linear regression model by using sodium excretion as a continuous dependent variable and the year of the study as a continuous independent variable, with each study weighted by the square root of the number of study participants or subgroup participants.