Ingibjörg Gunnarsdóttir^1,2

Ari J. Jóhannesson²

Jóhanna Eyrún Torfadóttir³

Zulema Sullca Porta⁴

Bryndís Eva Birgisdóttir¹

Hólmfríður Þorgeirsdóttir³

¹University of Iceland, ²Landspitali National University Hospital, Iceland, ³Directorate of Health, Iceland, ⁴Icelandic Food and Veterinary Authority.

Correspondence: Ingibjörg Gunnarsdóttir, ingigun@hi.is

Key words: iodine, intake, nutrition, fortification, adults, children.

INTRODUCTION: Insufficient iodine status was recently identified in pregnant women in Iceland. Iodine fortification of salt is widely used to decrease the risk of iodine deficiency disorders, but the use of iodized salt has not been recommended in Iceland. The aim was to describe iodine intake among Icelandic adults and two-year-olds and estimate the effect of using iodized salt in bread.

MATERIAL AND METHODS: Iodine intake was assessed using data from the Icelandic National Dietary Survey 2019-2021 (18-80 years, n=822) and a study of two-year-old children (n=124). Data on bread intake was used to estimate expected iodine intake if iodized salt was used in bread. The results are compared with recommended iodine intake (90 µg/day for two-year-olds and 150 µg/day for adults) and upper intake level (200 µg/day and 600 µg/day, respectively).

RESULTS: Average iodine intake was 88 µg/day for children and 134 µg/day for adults. If all types of bread consumed would contain 20 µg of iodine in 100 grams, the average iodine intake would increase to 99 and 153 µg/day, respectively. With higher bread iodine content, >5% of two-year-olds would exceed the upper intake level, while concentration up to 70 µg/100 grams of bread would result in iodine intake below the upper intake level for adults.

CONCLUSION: Use of iodized salt in bread corresponding to 20µg of iodine in 100 grams of bread seems safe for young children in Iceland. However, based on the current dietary habits, adding this amount of iodine to bread would not be sufficient to secure optimal intake of iodine in all adults.

Table I. Recommended intake, lower intake level, estimated average requirements and upper intake level (µg/day) for adults and children.^18,22

 

Term	Definition	Adults*	Children 1-5 years
Lower intake level	A cut-off intake value below which an intake could lead to clinical deficiency symptoms in most individuals	70	Not defined
Estimated average requirement	The level of a nutrient intake that is sufficient to cover the requirement for 50% of individuals	100	Not defined
Recomended intake	The amount of a nutrient that meets the requirement among practically all healthy individuals	150	90
Upper intake level	The maximum level of long-term (months or years) daily nutrient intake that is unlikely to pose a risk of adverse health effects in humans	600	200

* Recommended intake is 175 µg/day for pregnant women and 200 µg/day for lactating women.

 

 

Table II. Iodine intake (µg/day) without dietary supplements in the Icelandic National Dietary Survey 2019-2021 and estimated iodine intake (µg/day) simulating different iodine concentration in bread.

	Present intake of iodine	20 µg iodine /100 grams of bread	40 µg iodine /100 grams of bread	60 µg iodine /100 grams of bread	70 µg iodine /100 grams of bread
Average	134	153	169	185	193
Median	101	118	136	154	164
90th percentile	283	297	313	336	342
95th percentile	342	360	375	399	412
Proportion below lower intake level 70 µg/day)	28	16	11	8	7
Proportion below estimated average requirement (100 µg/day)	49	37	26	19	16

 

 

 

Table III. Iodine intake (µg/day) without dietary supplements among Icelandic two-year-olds and estimated iodine intake (µg/day) simulating different iodine concentration in bread.

	Present intake of iodine	20 µg iodine /100 grams of bread	40 µg iodine /100 grams of bread	60 µg iodine /100 grams of bread	70 µg iodine /100 grams of bread
Average	88	99	110	121	126
Median	77	90	101	113	121
90th percentile	153	161	174	191	198
95th percentlie	180	191	203	216	223

 

 

 

Table IV. Estimated intake of the main dietary sources of iodine in the Icelandic diet and iodine intake from National Dietary Surveys in1939 to 2019-2021*.

Year	Age	Fish (g/day)	Milk and dairy products (g/day)	Average iodine intake (µg/day)
1939	0-80	200	1000	570
1979-1980	0-80	70	729	336
1990	15-18	73	589	299
2002	15-80	40	388	163
2010-2011	18-80	46	300	167
2019-2021	18-80	45	245	134

*Information based on previously published data, ⁶ as well as information from the Icelandic National Dietary Surveys in 2010-2011²⁶ and 2019-2021. ⁵