Reduction of salt: will iodine intake remain adequate in The Netherlands?
Janneke Verkaik-Kloosterman1,2*, Pieter van ’t Veer2and Marga C. Ocke ´1
1National Institute for Public Health and the Environment, Bilthoven, The Netherlands
2Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands
(Received 7 January 2010 – Revised 4 June 2010 – Accepted 8 June 2010 – First published online 19 July 2010)
Salt is the main vehicle for iodine fortification in The Netherlands. A reduction in salt intake may reduce the supply of iodine. Our aim was to
quantify the effect of salt reduction on the habitual iodine intake of the Dutch population and the risk of inadequate iodine intake. We used data of
the Dutch National Food Consumption Survey (1997–8) and an update of the food composition database to estimate habitual salt and iodine
intake. To take into account uncertainty about the use of iodised salt (industrial and discretionary) and food supplements, a simulation model
was used. Habitual iodine and salt intakes were simulated for scenarios of salt reduction and compared with no salt reduction. With 12, 25
and 50% salt reduction in industrially processed foods, the iodine intake remained adequate for a large part of the Dutch population. For the
extreme scenario of a 50% reduction in both industrially and discretionary added salt, iodine intake might become inadequate for part of the
Dutch population (up to 10%). An increment of the proportion of industrially processed foods using iodised salt or a small increase in iodine
salt content will solve this. Nevertheless, 8–35% of 1- to 3-year-old children might have iodine intakes below the corresponding estimated average
requirement (EAR), depending on the salt intake scenario. This points out the need to review the EAR value for this age group or to suggest the
addition of iodine to industrially manufactured complementary foods.
Iodine: Salt intake: Salt reduction: The Netherlands
Too high salt (Na) intakes are associated with the risk of
elevated blood pressure and, as a consequence, increased
risk of CVD. Even a modest reduction of salt intake at the
population level will result in a decrease in blood pressure
and thus a prevention of CVD(1,2). A maximum salt intake
level of 5–6g/d is recommended for adults(3–6). This rec-
ommendation should not be seen as an optimum or tolerable
upper intake level, but rather as a feasible target. For the long
term a maximum salt intake level of 3g/d is proposed(7).
In The Netherlands, similar to other countries, the current
salt intake is too high. For adults the mean salt intake is esti-
mated at about 8–10g/d(8–11)and for children (aged 5–10
years) the mean salt intake is estimated at about 6g/d(12).
Authorities and food industries in several European countries,
and also in The Netherlands, have started initiatives to reduce
the population salt intake(13,14).
In many countries, including The Netherlands, iodine levels
naturally present in the diet are not adequate(15,16). To prevent
iodine-deficiency disorders, iodised salt is used. Reduction
of salt will therefore not only result in the desired reduced
salt intakes but also in unwanted reduced iodine intakes.
Currently, the iodine status of the Dutch population is ade-
quate(15,17,18), but this may become inadequate with reductions
of salt intake. Regular monitoring of the iodine status in the
population is a good measure to identify an existing potential
problem. In contrast, modelling the iodine intake for a popu-
lation presuming changes in salt intake can give quantitative
insight into the potential problems beforehand and may help
policy makers at an early stage to adapt their iodine policy.
To our knowledge no studies have been published quantifying
the effect of salt reduction strategies on the population iodine
intake. We recently developed a simulation model which
accurately estimates the total iodine intake of the Dutch popu-
lation using data from the Dutch National Food Consumption
Survey(19). In the present study we applied this model to esti-
mate the habitual total iodine and salt intake of the Dutch
population for several scenarios of salt reduction strategies
and we compared the salt intake distributions with the rec-
ommended maximum level to get quantitative insight into
the changes in population salt intake. The iodine intake distri-
butions were compared with the estimated average require-
ment (EAR) and tolerable upper intake level of iodine to
predict whether iodine intake will remain adequate for
different age groups within the population.
Data of the Dutch National Food Consumption Survey-3
(DNFCS-3) were used to estimate habitual total iodine and
salt intake. This survey is the most-recent population-
wide food consumption survey in The Netherlands and has
been described in detail elsewhere(20). Briefly, data were
collected in 1997–8 and respondents (n 6250; aged 1–97
years and selected from a representative consumer panel of
*Corresponding author: Dr Janneke Verkaik-Kloosterman, fax þ31 30 2744466, email Janneke.Verkaik@RIVM.nl
Abbreviation: EAR, estimated average requirement.
British Journal of Nutrition (2010), 104, 1712–1718
q The Authors 2010
British Journal of Nutrition
households) recorded their food intake with a food record on
2 consecutive days.
From 2007 onwards, iodine levels were added to the Dutch
food composition database (NEVO)(21). For the present study,
missing iodine levels were completed and available iodine
levels were, if required, updated using manufacturers’ infor-
mation, scientific literature(22,23), foreign food composition
tables (Danish (2005), Finnish (2006), German (1994, 2006),
UK (1991, 1993, 1995, 1996, 2002)), or iodine levels from
similar food products. All recipes were recalculated using
the updated iodine levels. Na levels available in NEVO(21)
were updated as well, using a similar procedure as for
iodine. As iodine is added to industrially processed foods as
iodised sodium chloride, the proportion of total Na industrially
added as sodium chloride was roughly estimated based on
recipe information. When the proportion of natural Na was
estimated to be 10% or less of total Na content, industrially
added salt was set at 100%. For most industrially processed
foods the proportion of added sodium chloride was set at
100%, except for salted fries (70%), canned vegetables
(80%), sesame paste (90%), all cheese excluding cheese
spread (75%), cheese spread (85%), chips (crisps) (85%),
liquorices (50%), smoked fish (85%), canned fish (80%),
dried and salted shrimps (30%) and meat products (90%).
Due to the lack of data about the discretionary use of (iodised)
kitchen salt and market shares of industrially processed foods
containing iodised salt, a simulation model combining deter-
ministic approaches with probabilistic approaches was used
to estimate both habitual iodine and salt intake. We have
described this model in detail elsewhere(19). Briefly, we defined
different potential dietary sources for both salt intake ((a) Na
present in industrially processed foods, and (b) discretionary
Na added during cooking or consumption) and iodine intake
((a) naturally present in foods, (b) added to industrially pro-
cessed foods, (c) discretionary iodine added via kitchen salt,
and (d) iodine-containing dietary supplements). For all these
sources, iodine and salt intakes were estimated separately
for each subject on each observation day. The intakes of
iodine from natural sources and salt (calculated from total
Na £ 2·5) present in industrially processed foods were calcu-
lated using a deterministic approach. The consumed amount
of a food was multiplied with the concentration of iodine or
salt in that food. For all other potential sources of iodine
or salt intake (i.e. industrially added, discretionary use of
kitchen salt, dietary supplements (iodine only)) we applied a
probabilistic approach to be able to take into account
uncertainty and variability. For each potential source we
estimated the proportion of foods that will contain iodised
salt or the proportion of consumers that will use (iodised)
salt or iodine-containing dietary supplements. A sample of
the study population (discretionary salt and dietary sup-
plements) or of the consumers (industrially added iodised
salt) as large as these proportions was drawn and selected to
consume the iodised or iodine-containing variants. To take
into account the uncertainty of who will actually use these
products, each sample was drawn for 100 iterations. To be
able to take into account that subjects will not be aware of
purchasing foods containing iodised salt we subdivided the
group of industrially processed foods into thirty-five food
groups that may contain iodised salt(19). For each food group
the probabilistic approach was applied separately and indepen-
dently for each observation day. It was assumed that subjects
assigned to discretionary use of (iodised) salt would do that for
all selected eleven food groups and on both observed days.
For each of these eleven food groups a point estimate of
discretionary use of (iodised) salt was estimated(19).
From the subjects selected to use iodine-containing dietary
supplements, a second sample was drawn to select subjects
using iodine-containing dietary supplements on both observed
days. The amount of iodine consumed from dietary sup-
plements was drawn from an age group-specific (children,
adolescents, adults) uniform distribution(19). The consumed
dose was assumed to be equal on both days. In The Nether-
lands, Na-containing dietary supplements are not used fre-
quently(8); therefore Na intake from this source was not
taken into account.
Total iodine and salt intake was calculated by summation
of the intake of iodine or salt from all potential sources per
subject, per observation day per iteration, resulting in 100
possible total intakes. Habitual total iodine and salt intake
was calculated by correcting the data for within-individual
variation using the Iowa State University (ISU) method
(SIDE/IML version 1.11, 2001; Iowa State University,
Ames, IA, USA)(24). Unless stated otherwise, SAS software
(SAS 9.1.3; SAS Institute Inc., Cary, NC, USA) was used
Population habitual total iodine intake distributions were
compared with the EAR set by the Institute of Medicine(25)
and tolerable upper intake levels set by the European Union
Scientific Committee on Food(26)to estimate the proportion
of the population at risk of too low or too high iodine intakes
using the cut-point method (taking EAR or upper intake
level as the cut-point)(27). The habitual total salt intake distri-
bution (calculated as total Na £ 2·5) was compared with the
recommended maximum salt intake level set by the Health
Council of The Netherlands (adults)(3)and the Scientific
Advisory Committee on Nutrition (children)(5).
Salt reduction scenarios
Habitual iodine and salt intake was estimated for different
scenarios of salt reduction strategies and for a reference situ-
ation without salt reduction (Table 1). In The Netherlands,
salt with a maximum of 65mg iodine/kg salt (high iodised
salt) may be used in bread, bread-replacing products and
other bakery products, and salt with a maximum level of
25mg iodine/kg salt (low iodised salt) may be used in all
containing . 1·2% alcohol by volume). This policy does not
only account for Dutch food producers but also for food
imported from other countries. From the Dutch salt industry
we know that their salt contains on average 58mg iodine/kg
salt (high iodised salt) or 20mg iodine/kg salt (low iodised
salt) (based on information of the Dutch salt industry;
L Rupert, Akzo Nobel Salt, The Netherlands, personal com-
munication). These levels were applied as point estimates in
the salt reduction scenarios under current iodine policy.
In the current market situation, at maximum 5% of all indust-
rially processed foods (excluding bread) contain iodised salt.
Iodine intake after salt reduction1713
British Journal of Nutrition
As it is unclear in which industrially processed foods iodised
salt is added, this percentage was used as the market share.
In bread, the use of iodised salt is more common due to a
covenant between the authorities and bakeries; therefore for
bread a market share of 90% was applied(19).
The scenarios of salt reduction strategies were based on
international experiences, mainly from UK and Ireland(13,28)
and initiatives of the Federation of the Dutch Food and
Grocery Industry (FNLI) in the Taskforce Salt. In the first
scenario, industrially added sodium chloride was reduced by
12% in all foods; this percentage was based on the current
commitment of Dutch bakeries (Table 1). In the second
scenario, a salt reduction of 25% was chosen and in the
third scenario an even higher salt reduction of 50% was
presumed. For the fourth scenario the median salt intake
(from all sources) of adults was reduced to the level of the
recommended maximum intake of salt (i.e. 6g/d)(3).
Habitual salt intake
In general, habitual salt intake increased with age, and was
higher for men than for women. For the current situation
(i.e. reference) the median habitual salt intake ranged from
4·2g/d for young children (aged 1–3 years) to 10·8g/d for
adult men (Table 2). The percentages of the population with
intakes above the recommended maximum level for salt
intake are high and ranged in this scenario from 88% to
almost 100% (Fig. 1). About 25% of total salt intake origi-
nated from discretionary added kitchen salt; this percentage
showed a small increase with age (data not shown).
As a logical consequence of salt reduction, salt intake
decreased in the four scenarios compared with the current situ-
ation (i.e. reference). Salt reductions of 12, 25 or 50% in
industrially processed foods decreased the habitual total salt
intake on average by 7, 15 and 30% compared with the
current intake (Table 2). With these salt reductions in all
age–sex groups the percentages with salt intakes above the
recommended maximum level remained high; 80–99, 68–97
and 28–93%, respectively (Fig. 1). In general, the highest
percentages were observed among young children (aged 1–8
years) and men. To reach a median habitual salt intake for
adult men of about 6g/d a 50% salt reduction in both indust-
rially processed foods and discretionary used kitchen salt was
needed (scenario 4). In this scenario, salt intake reduced on
average by 40% (Table 2) and the percentages with intakes
above the maximum recommended intake level in the different
age–sex groups decreased to 3–83% (Fig. 1). Young children
(aged 1–3 years) still had a median salt intake above the
maximum recommended level (2·6g/d); for children aged
4–6 years the median salt intake was close to the maximum
intake level (3·1g/d). To get the median habitual total salt
intake for young children (aged 1–3 years) close to the
recommended maximum intake level (i.e. 2·1g/d), a salt
reduction of 50% in industrially added salt in combination
with no discretionary use of kitchen salt was required.
Habitual iodine intake
In general, iodine intake was higher for men than for
women and increased with age. In the reference situation
(no salt reduction), the median habitual iodine intake ranged
from 105mg/d for young children aged 1–3 years to
268mg/d for boys aged 15–17 years (Table 3). A total of
8% of young children had a habitual iodine intake below
the current EAR (Fig. 2); however, for the other age–sex
groups, habitual iodine intakes below the EAR were small
(,5%). The percentage of the population with habitual
iodine intakes above the upper intake level was small in all
As iodised salt (industrial and discretionary) is an important
source of iodine intake, reduction of salt also reduced habitual
iodine intake. Salt reduction of 12, 25 or 50% in industrially
processed foods resulted on average in a 6, 12 or 25%
reduction in habitual iodine intake, but the 5th percentile of
iodine intake remained near or above the corresponding
EAR values for most age groups (Table 3; Fig. 2). The percen-
tage of the population with habitual iodine intakes below the
EAR slightly increased (1–11%) for age groups older than
3 years in the fourth scenario, which included reduction
of both industrially and discretionary added salt (Fig. 2).
Percentages below the EAR of iodine among young children
(aged 1–3 years) were 10% to 35% for scenarios 1 to 4 of
salt intake, respectively (Fig. 2).
Table 1. Different scenarios of use of iodised salt and salt reduction strategies
Percentage salt reduction in different food groups (%)
(mg iodine/kg salt) ReferenceScenario 1Scenario 2Scenario 3 Scenario 4*
Brand-specific bread-replacing products
known to contain iodised salt
Other bakery products
Other industrially processed foods
Discretionary use of iodised kitchen salt
(total kitchen salt)
81 (95) 00050†
*To achieve a median habitual salt intake of adults equal to the recommended maximum salt intake of 6g/d.
†Not only iodised kitchen salt, but total kitchen salt.
J. Verkaik-Kloosterman et al.1714
British Journal of Nutrition
In discussions about salt reduction concerns about the parallel
decrease in iodine intake are often mentioned, since salt is the
main vehicle for iodine fortification in many countries. In the
present study, we quantified the effects of potential scenarios
of salt reduction on habitual total iodine intake in the Dutch
population. In the current situation, without salt reduction,
the habitual iodine intake seems adequate for a large part
of the Dutch population. With salt reductions of 12, 25 and
50% in industrially processed foods this remained the case.
For the extreme scenario of 50% reduction in both industrially
and discretionary added salt, iodine intake might become
inadequate for part of the Dutch population.
Only for infants did we observe high percentages with
intakes below the EAR, i.e. about one-third of this age group
in the case of 50% salt reduction. However, the EAR for these
children (aged 1–3 years) was based on one single balance
study in which malnourished children were nutritionally reha-
bilitated(25). It can be questioned whether the level of iodine
that is needed for well-nourished children to maintain their
iodine balance is as high as the iodine level that is needed
to achieve nutritional rehabilitation. When the EAR of adults
was extrapolated down based on metabolic weight (i.e.
weight0·75) the EAR of young children would be 36mg/d,
which is considerably lower than 65mg/d (the current
EAR)(25). Taking the lower cut-off value of 36mg/d, less
than 5% of these children had intakes below this value (data
not shown). We recommend doing more research to assess the
iodine requirements of well-nourished young children before
conclusive statements on a potential public health risk for
young children are drawn.
Dutch iodine policy changed in 2008(17). In this new policy,
more foods are allowed to include iodised salt. The salt iodine
levels in this new policy are based on the assumption that
50% of industrially processed foods will use iodised salt.
Population above recommended
maximum level (%)
ReferenceScenario 1 Scenario 2 Scenario 3 Scenario 4
Fig. 1. Percentage of the Dutch population with habitual total salt intakes
(based on total Na intake) above the recommended maximum level, for
different scenarios of salt reduction strategies: reference, no salt reduction;
scenario 1, 12% salt reduction in industrially added salt; scenario 2, 25%
salt reduction in industrially added salt; scenario 3, 50% salt reduction
in industrially added salt; scenario 4, 50% salt reduction in industrially and
discretionary added salt. The percentages are based on 100 iterations for
estimating the intake profile; values are presented as the median of 100
iterations. The recommended maximum levels for the different age groups
are: 1–3 years, 2g/d; 4–6 years, 3g/d; 7–10 years, 4g/d; 11–14 years,
5g/d; $ 15 years, 6g/d(3). (– þ –), Children 1–3 years; (– £ –), children
4–6 years; (
), boys 7–14 years; (
boys 15–17 years; (
), girls 15–17 years; (–V–), adult men; (--V--),
), girls 7–14 years; (),
Table 2. Habitual salt* intake (g/d) in the Dutch population for different salt reduction strategies
(Medians and 95th percentiles†)
no salt reduction
Scenario 1: 12%
Scenario 2: 25%
Scenario 3: 50%
Scenario 4: 50%
Age group (years)
*Based on total Na intake.
†Median and 95th percentile based on the results of 100 iterations; variation between the 100 iterations was on average ^2% for median and ^3% for 95th percentile.
‡For adults from the Health Council of The Netherlands(3), for children and adolescents from the Scientific Advisory Committee on Nutrition(5).
§Only salt reduction in industrially processed foods.
Iodine intake after salt reduction1715
British Journal of Nutrition
Currently this proportion is about 5%, and an increment of the
proportion of industrially processed foods using iodised salt
from 5% to 50% will result in adequate iodine intakes for vir-
tually the whole population, including young children(19).
With large salt reductions, also an increase in the proportion
of industrially processed foods using iodised salt from 5%
to 50% is enough to reduce the percentage of the population,
excluding young children, with iodine intakes below the cur-
rent EAR to less than 5% (data not shown). Even mandatory
iodisation will not result in adequate iodine intakes for young
children (data not shown). To increase the habitual iodine
intake of children aged 1–3 years to intake levels above the
EAR (i.e. 65mg/d) under major salt reduction strategies, salt
iodine levels should be increased (for instance, a salt iodine
level of 80mg iodine/kg salt) in combination with a 50%
market share of industrially processed foods using iodised
salt (data not shown). An alternative is to recommend and
stimulate the addition of iodine to industrially manufactured
The present study shows that the long-term goal of the
Federation of the Dutch Food and Grocery Industry (FNLI)
of a mean salt reduction of 20–30%(14), which is similar to
salt reduction goals in other counties(13,28), is not sufficient
to reduce total salt intake to or below the level of the maxi-
mum recommended salt intake. A larger salt reduction of
50% (both industrially and discretionary) is required to
reach a median habitual total salt intake for adults of about
6g/d. An even larger salt reduction of 50% in industrially
processed foods in combination with no discretionary use
of salt is needed for young children (aged 1–6 years)
to reach a median habitual salt intake at their age-specific
recommended maximum salt intake (data not shown)(5). This
underlines the additional importance of changing consumer
behaviour in the use of discretionary added salt. In order to
prevent compensation behaviour of industrial salt reduction,
this should be a gradual process supported by the whole
Table 3. Habitual iodine intake (mg/d) in the Dutch population for different salt reduction strategies
(Medians and 5th percentiles*)
Scenario 1: 12%
Scenario 2: 25%
Scenario 3: 50%
Scenario 4: 50%
EAR, estimated average requirement.
*Median and 5th percentile based on the results of 100 iterations; variation between the 100 iterations was on average ^5% for median and ^10% for 5th percentile.
†Set by the Institute of Medicine (USA)(25).
‡Only salt reduction in industrially processed foods.
Population below current EAR (%)
ReferenceScenario 1Scenario 2Scenario 3Scenario 4
Fig. 2. Percentage of the Dutch population with habitual iodine intakes below
the current estimated average requirement (EAR), for different scenarios of
salt reduction strategies: reference, no salt reduction, scenario 1, 12% salt
reduction in industrially added salt; scenario 2, 25% salt reduction in indust-
rially added salt; scenario 3, 50% salt reduction in industrially added salt;
scenario 4, 50% salt reduction in industrially and discretionary added salt.
The percentages are based on 100 iterations for estimating the intake profile;
values are presented as the median of 100 iterations. The current EAR
for the different age groups are: 1–6 years, 65mg/d; 7–10 years, 73mg/d;
11 years and older, 95mg/d(25). (– þ –), Children 1–3 years; (– £ –),
children 4–8 years; (
), boys 9–13 years; (
), boys 14–17 years; (), girls 14–17 years; (
(--V--), adult women.
), girls 9–13 years;
), adult men;
J. Verkaik-Kloosterman et al.1716
British Journal of Nutrition
food industry. In Finland, salt reduction initiatives already
started several decades ago. Also the discretionary use of
salt reduced(29); this may indicate that compensation beha-
viour was minor.
A limitation of the present study is that Dutch national food
consumption data from 1997–8 were used; these are the most
recent monitoring data covering all ages. To get more up-to-
date results, these consumption data were combined with the
most up-to-date food composition data taking into account
changes in food composition since 1997–8. In 2005–6 a
food consumption survey was conducted among young chil-
dren (aged 2–6 years). Application of our model to these
data resulted in median habitual total salt intakes that were
slightly lower (4·0g/d for children aged 2–3 years; 4·7g/d
for children 4–6 years). Also the median estimated habitual
iodine intakes were lower (89mg/d for children aged 2–3
years; 113mg/d for children aged 4–6 years). The observed
differences are small and results are in same order of
magnitude as the results presented in the present paper.
These calculations imply that the indications of habitual salt
and iodine intake in the different scenarios of salt reduction
seem still valid for the current Dutch situation.
A strength of the study is that the model we used to estimate
habitual iodine and salt intake was earlier shown to accurately
estimate habitual iodine intakes in The Netherlands(19).
The habitual total salt (Na) intakes that we estimated with
this model for adults were somewhat higher but in same order
of magnitude as the results from other Dutch studies(8–12).
The small differences between our model and these three
studies may not only be due to the model assumptions, but
might also be caused by differences in the study populations
(for example, age distribution). The comparability in results
indicates that our model is a useful tool to estimate both habit-
ual salt and iodine intake accurately in the Dutch population.
The salt reduction scenarios applied in the present study
were generic reductions in all industrially processed foods.
Differences in technological feasibility of salt reductions
between food groups were not considered; however, with
our model these can be taken into account in future studies.
The present study, nevertheless, does show what large salt
reductions are needed in the Dutch population and gives first
indications on the effect on iodine intake.
In conclusion, the present study showed that with small salt
reductions, iodine intakes remain adequate in a large part of
the Dutch population. These small reductions in the total
habitual salt intake will not come close to the maximum
recommended salt intake levels. A more pronounced salt
reduction is therefore needed, for instance, 50% reduction
of both industrially and discretionary added salt. A small
part of the Dutch population (up to 10%) might then have
inadequate habitual iodine intakes. An increment in the
number of industrially processed foods using iodised salt or
a small increase in iodine salt content will solve this.
We would like to thank H. A. M. Brants and M. Jansen-van
der Vliet for updating the food composition data for most
recent information on iodine and Na concentrations and
C. Wilson-van der Hooven for assistance in defining the salt
The present study received no specific grant from any fund-
ing agency in the public, commercial or not-for-profit sectors.
All authors contributed to the interpretation of the data and
writing of the manuscript. J. V.-K. performed the simulations
of the different scenarios.
The authors declare that there are no conflicts of interest.
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