Value of overnight urines in the follow-up of people with borderline hypertensive trying to reduce their salt intake
Tuomilehto, J.; Tanskanen, A.; Pietinen, P.
Acta Cardiologica 40(3): 325-328
1985
ISSN/ISBN: 0001-5385 PMID: 3927646 Document Number: 257077
The value of overnight urine samples was compared with 24-h urine collections as a measure of salt intake in a long-term (2 yr) salt restriction trial which was part of the Finnish North Karelia Salt Project. Persons with slightly elevated blood pressure (without drug therapy) were advised to reduce their salt intake as much as possible. Each urine collection was divided into 2 time periods: overnight and rest of the 24-h period. The mean 24-h urinary Na excretion among men decreased during a 2-yr period from 243 mmol to 177 mmol (P < 0.01) and among women from 194 mmol to 153 mmol (P < 0.01), respectively. The correlation coefficient between overnight urine Na excretion rate and 24-h urine Na excretion rate was among men 0.49 at baseline and 0.80 at 2 yr and among women 0.82 at baseline and 0.49 at 2 yr. The strength of the correlation between overnight and 24-h urine Na excretion rates is modified by the total Na excretion level. The overnight urine specimen might be valuable in estimating salt intake in groups of people. Because restriction of salt intake is mainly reflected in the rest of the 24-h period but not in the overnight collection, the overnight specimen cannot be used to estimate an individual's salt intake or salt intake reduction.