Twenty-four-hour urinary electrolyte excretion by age group and sex among participants aged 4–12 years*
| Urinary marker | 4–12 years | 4–8 years | 9–12 years | ||||||
| All | Boys | Girls | All | Boys† | Girls | All | Boys† | Girls | |
| No of participants | 666 | 365 | 301 | 283 | 159 | 124 | 383 | 206 | 177 |
| Sodium (mmol/day) | 103±2 | 109±3‡ | 97±3 | 90±2§ | 94±2‡ | 85±3 | 113±3 | 120±4‡ | 105±3 |
| Salt equivalent (g/day) | 6.1±0.1 | 6.4±0.2‡ | 5.7±0.2 | 5.3±0.1§ | 5.5±0.1‡ | 5.0±0.2 | 6.6±0.2 | 7.0±0.2‡ | 6.1±0.2 |
| Potassium (mmol/day) | 47±1 | 49±1‡ | 44±1 | 41±1§ | 42±1‡ | 39±1 | 51±1 | 54±2‡ | 47±2 |
| Na:K (molar ratio) | 2.4±0.05 | 2.4±0.06 | 2.3±0.06 | 2.4±0.6 | 2.4±0.8 | 2.3±0.09 | 2.4±0.6 | 2.4±0.9 | 2.4±0.6 |
| Creatinine (mmol/day) | 5.6±0.1 | 5.8±0.2 | 5.3±0.2 | 4.3±0.1 | 4.5±0.1 | 4.1±0.1 | 6.5±0.1 | 6.8±0.2 | 6.1±0.2 |
| Volume output (mL/day) | 866±22 | 889±29 | 838±26 | 748±20 | 748±21 | 748±35 | 953±26 | 997±40 | 902±34 |
*Linear regression with adjustment for school cluster was used to assess differences in the excretion of sodium, salt equivalent, potassium and Na:K molar ratio between subgroups.
†Additional adjustment for age, day of urine collection and BMI z-score did not alter results in any of the age or sex-subgroup analyses (data not shown). This was with the exception of urinary potassium excretion, which was no longer significantly higher in boys (fully adjusted model p=0.06) within the age stratified sub-group analyses of 9–12 years.
‡<0.05, significant difference between boys and girls.
§<0.05, significant difference between age groups, that is, 4–8 years versus 9–12 years.