Association between 24-hour urine sodium and
potassium excretion and diet quality in
six-year-old children: a cross sectional study
Oddny K Kristbjornsdottir1, Thorhallur I Halldorsson1,2, Inga Thorsdottir1,2and Ingibjorg Gunnarsdottir1,2*
Background: Limited data is available on sodium (Na) and potassium (K) intake in young children estimated by
24 hour (24h) excretion in urine. The aim was to assess 24h urinary excretion of Na and K in six-year-old children
and its relationship with diet quality.
Methods: The study population was a subsample of a national dietary survey, including six-year-old children living
in the greater Reykjavik area (n=76). Three day weighed food records were used to estimate diet quality. Diet quality
was defined as adherence to the Icelandic food based dietary guidelines. Na and K excretion was analyzed from 24h
urine collections. PABA check was used to validate completeness of urine collections. The associations between Na
and K excretion and diet quality were estimated by linear regression, adjusting for gender and energy intake.
Results: Valid urine collections and diet registrations were provided by 58 children. Na and K excretion was, mean
(SD), 1.64 (0.54) g Na/24h (approx. 4.1 g salt/24h) and 1.22 (0.43) g K/24h. In covariate adjusted models Na excretion
decreased by 0.16 g Na/24h (95% CI: 0.31, 0.06) per 1-unit increase in diet quality score (score range: 1–4) while K
excretion was increased by 0.18 g K/24h (95% CI: 0.06, 0.29).
Conclusions: Na intake, estimated by 24h urinary excretion was on average higher than recommended. Increased
diet quality was associated with lower Na excretion and higher K excretion in six-year-old children.
Keywords: Sodium, Potassium, Children, 24h urinary excretion, Diet quality
The best method of estimating sodium (Na) and potas-
sium (K) intake is by analyzing 24-hour (24h) Na and K
excretion in urine [1,2], as the use of dietary surveys and
food composition databases for estimating Na and K in-
take may introduce either an over- or underestimation
of the actual intake. Studies including 24h urine collec-
tions for estimation of Na and K intake in children are
Food based dietary guidelines have been established as
a result of studies showing that the overall diet quality
rather than specific nutrients protects against chronic
diseases in adults [3-5]. The main dietary sources of K
contribute to a healthy diet and are in line with food
based dietary guidelines [6-8]. On the other hand, the
main dietary sources of Na in children are considered to
be less healthy, including processed meat and fast food
dishes [8,9]. Tracking of dietary habits from early child-
hood into adulthood has shown that children with ex-
tremely high levels of Na intake tend to maintain those
levels over time [10-12]. Therefore, diet in childhood
can be a significant determinant of adult dietary habits
even after several decades .
The aim of the present study was to gather informa-
tion about Na and K intake in six-year-old children by
24h urinary excretion. The aim was also to assess the re-
lationship between Na and K excretion and diet quality.
The source population were subjects invited to partici-
pate in a longitudinal study on nutrition and health of
* Correspondence: firstname.lastname@example.org
1Unit for Nutrition Research, Landspitali-University Hospital, Eiriksgata 29,
Reykjavik 101, Iceland
2Faculty of Food Science and Nutrition, School of Health Sciences, University
of Iceland, Eiriksgata 29, Reykjavik 101, Iceland
© 2012 Kristbjorsdottir et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the
Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original work is properly cited.
Kristbjornsdottir et al. Nutrition Journal 2012, 11:94
Icelandic six-year-olds who had previously participated
in studies on nutrition and health during infancy  or
at two years of age . Originally, families of 180
infants from four maternity wards around Iceland were
invited to participate in the infant study and 130 two-
year-old children were randomly selected by the Ice-
landic National Registry. In the infant study 138 agreed
to participate, 27 were lost in follow-up at 12 months of
age leaving 111 eligible subjects for the follow up at six
years. From the study on two year olds 69 were eligible
for the follow-up study at the age of six years, altogether
180 subjects. Each family was contacted by telephone
and invited to take part in the study. If consent was
obtained, an introductory letter explaining the details of
the study was sent by mail. The study was approved by
the Local Ethical Committee at Landspitali-University
Hospital in Iceland, The National Bioethics Committee
and by Icelandic Data Protection Commission. The par-
ticipation rate in the follow-up study was 73% where 131
completed three day food records . Only children
who were living in the greater Reykjavík area were
invited to provide 24h urine collections (n=111) due to
practical reasons (i.e. closeness to the study centre), of
which 79 agreed. Three of the children providing 24h
urine collections returned incomplete food records,
resulting in 76 subjects eligible for the present analysis.
Weighed food records
Parents kept weighed food records for their children for
three consecutive days including one weekend day and
2 week days using a kitchen scale (PHILIPS HR 2385,
Austria) around the time of the child’s sixth birthday.
Each family received a booklet with which to record
all food eaten during this time period. Parents were
instructed on how to use the scales and to record the
date and time of the meals, specifically to record the
brand name or type of food, to include recipes of home-
made dishes, and record all drinks and vitamin intake.
The data was entered into an interview-based nutrient
calculating program, ICEFOOD, designed for the national
dietary survey of The Icelandic Nutrition Council .
Nutrient losses due to food preparation were included in
the calculations. This program included 452 food codes
or recipes from the Icelandic Nutrition Council, based
on 394 food items from the National Nutrition Database,
Na and K excretion
Parents and caretakers were given both verbal and writ-
ten instructions in assisting children to collect a 24h
urine sample on one of the three days of food recording.
Each child was provided with a urine collection bottle, a
backpack in which to carry the jug and three 80 mg
PABA tablets (PABA check, The royal veterinary and
agricultural pharmacy, Cophenhagen). On the first
morning of the urine collections, instructions were given
to discard the first specimen, and from then on to col-
lect all specimens for up to 24h, up to and including the
first specimen the following day. Subjects were asked to
take three 80 mg PABA tablets, one tablet during each
main meal on the same day as the urine collections. On
return to the laboratory, urine volume was recorded.
PABA check  was used to validate completeness of
urine collections. Collections that contained 85% or
more of the PABA ingested were considered complete
. Recovery between 50% and 85% was adjusted
according to a formula developed by Johansson and
Bingham 1999 : Na excretion = excretion [mg/day] +
(0.82 * (93-PABA recov) and K excretion = excretion
[mg/day] + (0.60 * (93-PABA recov)).
Na and K concentration was measured immediately by
flame emission photometry  at Landspitali University
Hospital. The remainder of the samples were stored at
−20°C for later analysis of PABA which was measured
colorimetrically at Forskningsinstitut for Human Ernær-
ing in Cophenhagen, Denmark .
Adherence to the Icelandic food based dietary guidelines
(FBDG) was used to assess diet quality score. Portion
sizes used to determine diet quality score were adjusted
to reflect the 20% lower energy needs of six-year-olds
compared to an adult . The FBDG are based on six
recommendations.: ≥400 g fruits and vegetables, ≥34 g
fish, ≥5 g fish liver oil and ≥400 g milk and milk pro-
ducts (or 200 g milk and milk products and 20 g cheese).
The Public Health Institute of Iceland  recommends
K intake ≥2 g/d for children 6–9 year old and the Nordic
Nutrition Recommendations  ≤0.5 g salt/1000 kJ
(0.5 g salt/239 kcal) for children 2–18 years old, corre-
sponding to about 3.2 g salt daily (according to energy
intake of 1530 kcal/d in the present study). Fiber con-
sumption of at least 11 g/day was used in the evaluation
of diet quality score as an indicator of whole grain cereals
. One point was obtained by following each guideline,
for a maximum of six points. Diet quality score was
divided into four groups based on adherence to FBDG,
those following one, two, three or at least four of the
Height and weight of study participants were measured
at Landspitali – Children’s Hospital. Subjects wore light
weight clothing and no shoes. Height was measured to
the nearest 0.1 cm using a ulmer stadiometer, Busse de-
sign (Nersinger Straβe 18, 89275 Elchingen, Germany),
and weight was measured to the nearest 0.05 kg using a
Kristbjornsdottir et al. Nutrition Journal 2012, 11:94
Page 2 of 6
Taniter BWB-620 electronic scale (2625 South Clear-
brook Drive, Arlington Height, Illinois 60005, USA).
Statistical analyses were conducted using SPSS for Win-
dows, version 17 (SPSS Inc, Chicago). Descriptive ana-
lyses (mean and standard deviation) were used to
describe the characteristics of study participants. A vis-
ual inspection of histograms suggested that Na and K
urinary excretion was normally distributed. Independent
samples t-test was used to test the difference between
boys and girls and to determine whether Na and K ex-
cretion was significantly different between those who
follow each food based dietary guideline and those who
To examine the association between diet quality score
and Na and K excretion we used multivariate linear re-
gression analyses where gender and energy intake were
included as covariates. We included gender as a covari-
ate to account for potential sex dependent differences in
behavioral and physiological factors. Total energy intake
was included as those with high intake were more likely
to meet the food based dietary recommendations (as
cutoffs in grams/day were used), while simultaneously
having higher intakes of Na and K.
Of 76 children returning the 24h urine collection and
also had complete dietary data, 18 were excluded due to
incomplete urine collections according to PABA recov-
ery. More than 85% of the PABA was retrieved in the
urine collections of 28 subjects, while excretion from
48 subjects was adjusted (PABA recovery between 50%
and 85%). Characteristics of the subjects (n=58), and in-
formation on Na and K excretion is shown in Table 1.
The average Na excretion was 1.66 g/24h, corresponding
to 4.16 g NaCl (table salt). Less than one third (29%)
had Na excretion corresponding to an intake below the
recommended salt intake of 3.20 g/d . The average K
excretion was 1.21 g/24h. No significant gender differ-
ence was observed. Based on the three-day food records,
mean Na intake was 1.94 g/day (4.86 g table salt/day)
and mean K intake was 1.91 g/day. Cereals were found
to provide 43% of the total Na in the diet, spices 17%,
dairy products provided 15%, meat 11% and 14% came
from other sources. Dairy products (32%), fruits and
vegetables (22%) and cereals (15%) where found to be
the main dietary sources of K.
Table 2 shows the proportion of children meeting each
of the guidelines used to estimate the diet quality index.
Greatest adherence was found for dairy products and
fish where 61% and 41% of the children, respectively,
had consumption in line with the recommendations.
Children who consumed dairy products and dietary fiber
in line with the recommendations had significantly
greater K excretion than those who did not meet the
recommendations (p=0.01) and (p=0.02), respectively.
The average Na and K excretion according to diet
quality score is shown in Table 3. In covariate adjusted
models Na excretion decreased by 0.16 g Na/24h (95%
CI: 0.31; 0.06) per 1-unit increase in diet quality score
(score range: 1–4) while K excretion was increased by
0.18 g K/24h (95% CI: 0.06; 0.29). Excluding the salt
recommendation from the definition of diet quality did
not change the findings.
In the present study Na and K excretion were associated
with diet quality among six-year-old children. Na excre-
tion in this study of six-year-old children was 1.66 g/24h
(0.07 g/kg/24h), that corresponds to about 4.2 grams
table salt. The average consumption of salt worldwide is
generally high, particularly in industrialized countries,
and the results from the present study are in line with
previous findings [26-28]. In the Nordic nutrition
recommendations from 2004  ≤0.5 g salt is recom-
mended per 1000 kJ (0.5 g salt/239 kcal) for children
2–18 years old. The average energy intake in the present
study was 1530 kcal/day, so the average salt intake
should have been close to or below 3.2 g salt daily. Less
than one third (29%) of the children in the present study
had Na intake in line with the recommendation . Na
Table 1 Characteristics of study participants
N=58 (52% boys)
Age, months (sd)72 (1.0)
Height, cm (sd)119 (4.6)
Weight, kg (sd) 23 (3.1)
Systolic blood pressure, mmHg (sd)110 (11.1)
Diastolic blood pressure, mmHg (sd)64 (11)
Urine volume, mL/24h (sd)648 (284)
mmol/24h (sd)71 (23)
g/kg/24h (sd)0.07 (0.02)
mmol/24h (sd) 31 (11)
g/kg/24h 0.05 (0.02)
Na/K excretion1.6 (1.3)
1Na excretion corrected for PABA = excretion in mg/day + (0.82*(93-PABA
2K excretion corrected for PABA = excretion in mg/day + (0.60*(93-PABA
Kristbjornsdottir et al. Nutrition Journal 2012, 11:94
Page 3 of 6
is part of various additives and hence added to most
foods, either by the industry or in cooking. The high Na
intake observed in this population is of concern and
should be recognized by health authorities. In the popu-
lation studied lower content of salt in cereals (including
bread) could significantly contribute to lower Na intake as
this food group provided 43% of the total Na consumed. A
reduced salt intake of 42% (IQR: 7%-58%) was found to be
associated with 1.17 mmHg decrease in systolic (95% CI:
-1.78 to −0.56; p<0.01) and 1.29 mmHg diastolic (95% CI
−1.94 to −0.65, p<0.01) blood pressure in a meta analysis
including children with mean age of 13 years . From
a population viewpoint, a reduction in BP of 1.1 mmHg
in this age group would have major effects of preventing
cardiovascular disease in the future .
K excretion in the present study was 1.21 g/24h or
0.05 g/kg/24h. Few studies exist on K excretion but
two studies examined 8–9 year old children and reported
excretion of about 1.80 g/24h  and 2.00 g/24h
(0.07 g/kg/24h) . Another study on 3–5 year old chil-
dren showed K excretion of 1.00 g/24h or 0.05 g/kg/24h
. It is often challenging to compare values from
studies on children, mainly due to the different ages and
body weights of the young subjects. To ease the com-
parison, it might be convenient to use the per kilogram
approach. K excretion was associated with many of the
components of the diet quality index used in the present
study, such as dairy and whole grain (fiber). K excretion
appeared to be higher among those children following
the recommendations on fruit and vegetable intake, but
the number of subjects following the recommendations
was too few to draw any meaningful conclusions. This is
consistent with previous studies of low fruit and vege-
table consumption of Icelandic children, which is lower
than in many other European countries .
A linear trend was observed between decreased Na
and increased K excretion and increased adherence to
diet quality in the current study. Only a few studies have
assessed the association between diet quality and excre-
tion of Na or K and none of them included children. K
excretion was found to be associated with diet quality in
a study of adults with kidney stones (r=0.23, p<0.01)
. The recommended food score was used as an index
of healthy diet, which contained food groups such as
vegetables, fruits, whole grains, low fat dairy, fish and
poultry, similar to the present study. Adult nephrolithia-
sis patients from the Health Professionals Follow-up
Study and the Nurses' Health Studies (NHS) I and II col-
lected 24h urine samples and semiquantitative food fre-
quency questionnaires. In the Dietary Approaches to
Stop Hypertension (DASH) trial, a dietary DASH score
was given based on seven components: high intake of
Table 2 Na and K excretion (g/24h) according to adherence to food based dietary guidelines 
Recommendation Children follow
(n=58 [n (%)]
Na excretion (Mean (sd))K excretion (Mean (sd))
Fruits and vegetables
5 (8.5)1.89 (0.99) 1.62 (0.48)1.44 (0.33) 1.19 (0.43)
24 (40.7) 1.60 (0.51)1.68 (0.56) 1.34 (0.52)1.12 (0.34)
Fish liver oil
9 (15.3) 1.84 (0.62) 1.61 (0.52)1.12 (0.38)1.23 (0.44)
36 (61.0) 1.65 (0.62)1.65 (0.39) 1.32 (0.46)
Fibre22 (37.3) 1.59 (0.49)1.67 (0.56)
Salt17 (28.8) 1.11 (0.18)1.33 (0.48) 1.16 (0.40)
sd: Standard Deviation.
1 adjusted according to .
4p<0.05 between following FBDG and not following FBDG.
5p<0.01 between following and not following FBDG.
Table 3 Mean (sd) excretion of Na and K (g/24h) in urine and Na/K ratio according to diet quality and the association
between diet quality and excretion
Diet quality score1
(n=13)(n=24)(n=10)(n=11)B (95% CI)
−0.10 (−0.25; 0.04)
B (95% CI)
−0.16 (−0.31; -0.06)Na (sodium)1.70 (0.35)1.75 (0.73)1.45 (0.27)1.45 (0.87) 0.060.03
K (potassium)1.09 (0.29)1.08 (0.39)1.51 (0.55)1.59 (0.29)0.19 (0.08; 0.29)<0.010.18 (0.06; 0.29)<0.01
Na/K ratio 1.7 (0.6)2.1 (2.1)1.1 (0.4)1.0 (0.7)
−0.25 (−0.60; 0.10)0.07
−0.28 (−0.66; 0.11)0.06
1Follows one of the FBDG; 2: Follows two of the FBDG; 3: Follow three of the FBDG; 4: Follows at least four of the FBDG. [6,23-25].
2Adjusted for gender and energy intake.
Kristbjornsdottir et al. Nutrition Journal 2012, 11:94
Page 4 of 6
fruits, vegetables, nuts and legumes, dairy products, and
whole grains and low intake of sweetened beverages and
red and processed meats. It was found that higher
DASH scores were associated with higher K in all three
cohorts (P for trend all ≤0.01) . In 12 healthy adults,
a two-week long elimination of fruits and vegetables
from the diet resulted in a decrease in urinary K of 62%
(p<0.05), assessed from 24h urine collection .
Strength and limitations
The strength of the study is an accurate food record for
three days and a valid 24h urine sample. The fact that
we only had one 24h urine excretion per individual
might be considered a limitation as more than one col-
lection is needed for individual assessment of Na and K
excretion. However, in the present analysis the Na and K
excretion measurements were used on group level
according to adherence to food based recommendations.
Furthermore, the Na and K intake estimated by the food
records are also presented in this report, providing add-
itional information. The urine collections were con-
ducted on one of the three days of food recording and
Na and K excretion is known to be an indicator of re-
Na intake estimated by 24h urine excretion was, on aver-
age, higher than recommended. Increased diet quality
was associated with lower Na excretion and higher K
excretion in six-year-old children.
24h: 24-hour; K: Potassium; Na: Sodium; FBDG: Food based dietary guidelines.
The authors declare that they have no competing interests.
IT and IG contributed to design, data collection, interpretation and final
writing of the paper. TIH contributed statistical analysis, interpretation and
final writing. OKK contributed handling/management, statistical analysis,
interpretation and wrote the first draft of the manuscript. All authors read
and approved the final manuscript.
The authors thank the families who participated in the study, Margaret
Ospina for data collection in the study of 6-year-olds and the staff of the
laboratories at Landspitali University hospital in Reykjavík for their
involvement. Also Hildur Atladóttir and Björn Gunnarsson for their valuable
This work was supported by The Research Fund of the University of Iceland.
The data collection was supported by The Icelandic Center for Research.
Received: 15 June 2012 Accepted: 25 October 2012
Published: 15 November 2012
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