Maternal and infant iodine nutrition and thyroid function : A cohort study of pregnant and postpartum women and their infants in Norway

Background: Iodine is a micronutrient essential for the production of the thyroid hormones. The thyroid hormones are particularly important for neurodevelopment of the foetus during pregnancy and for the developing child in the first years of life. Whereas the adverse effects of severe iodine deficiency are well documented, the consequences of mild-to-moderate iodine deficiency during pregnancy and infancy are still uncertain and data are limited. Objectives: The main objective of this thesis was to describe iodine nutrition and thyroid function and to explore associations between them in a cohort study of pregnant and postpartum women and their infants. The specific objectives were to: I) Assess the validity and reproducibility of an iodine-specific food frequency questionnaire (I-FFQ) developed for pregnant women. II) Explore whether iodine nutrition and timing of iodine supplement initiation were associated with altered thyroid function in mildly-to-moderately iodine-deficient pregnant and postpartum women. III) Describe infant iodine status and thyroid function and further explore associations between them in the first year of life. In addition, assess the impact of maternal iodine nutrition and breastfeeding status on infant iodine status. Methods: A total of 137 pregnant women were enrolled and followed-up at gestational weeks (GW) 18 and 36, and further with their infants at 3, 6 and 11 months postpartum. Dietary iodine intake from an I-FFQ and a six-day food diary, urinary iodine and creatinine concentrations (UIC and UIC:Cr), breast milk iodine concentration (BMIC) and thyroid function tests (thyroid-stimulating hormone (TSH), free triiodothyronine (fT3) and free thyroxine (fT4)) were measured. Results: Maternal iodine intake estimated from the I-FFQ showed acceptable correlation and agreement with iodine intake estimated from the six-day food diary and UIC, indicating that the I-FFQ can be used as a tool to estimate and rank iodine intake in this population. The median maternal UIC was below 100 µg/L during pregnancy (GW18: 94 µg/L; GW 36: 85 µg/L) and in the postpartum period (3 months: 74 µg/L; 6 months: 84 µg/L), indicating mild-to-moderate iodine deficiency of the mothers. The median infant UIC was 82 µg/L at age 3 months, thus, below the recommended WHO cut-off (100 µg/L), also indicating insufficient iodine status. Median infant UIC increased during the first year of life and was 110 µg/L at ages 6 and 11 months, indicating adequate iodine status at these ages. Infant UIC was associated with maternal iodine intake, UIC:Cr and BMIC. At ages 3 and 6 months, breastfed infants had a lower median UIC (76 and 105 µg/L, respectively) compared with formula-fed infants (190 and 315 µg/L, respectively). At age 11 months, no differences between breastfeeding categories were found. The prevalence of maternal and infant thyroid dysfunction in this study population was low. Lower maternal iodine availability (measured by iodine intake and UIC:Cr) was associated with higher fT3 and fT4 concentrations, and lower TSH concentrations (intake only). Compared with no use of supplements, those initiating an iodine-containing supplement before conception and continuing through pregnancy had lower TSH, and higher fT3 and fT4 concentrations. No associations were found between infant UIC nor BMIC with infant thyroid function (TSH, fT3, fT4). Conclusion: Pregnant and postpartum women and breastfed infants in their first months of life are at risk of iodine deficiency in Norway. No associations were found between infant iodine status and thyroid function. Maternal iodine nutrition was, however, associated with altered thyroid function tests, and initiation of iodine supplementation before conception and continuing through pregnancy was associated with possible improved thyroid function. Overall, to ensure normal thyroid function in the developing foetus and growing infant, maternal iodine nutrition should be optimised before conception and continued throughout pregnancy and the postpartum period. Awareness of promoting adequate iodine nutrition for these vulnerable population groups should be prioritised to secure sufficient iodine intake for mothers and, subsequently, their infants.Doktorgradsavhandlin

Modal split and travel times in the western NSB corridor in Oslo

How do investments in roads and public transport respectively, influence modal split and traveling times? The Norwegian Institute for Urban and Regional Research are in collaboration with Martin Mogridge Associates (London) undertaking a project aiming at answering this question. The discussion will be based on literature reviews and our own empirical research. Both cross sectional analyses and time sere analyses will be conducted in the empirical research. This paper presents empirical results from the first investigation in one of the two case corridors

Validation and reproducibility of a new iodine specific food frequency questionnaire for assessing iodine intake in Norwegian pregnant women

Iodized salt is not mandatory in Norway, and the permitted level of iodine in table salt is low (5 μg/g). Thus, milk and dairy products, fish and eggs are the main dietary sources of iodine in Norway. Mild-to-moderate iodine deficiency in pregnant women has been described in several European countries, including Norway. There are few validated tools available to assess iodine intake in an efficient manner. The aim of the current study was to assess the validity and reproducibility of a new iodine-specific food frequency questionnaire (I-FFQ) in Norwegian pregnant women.publishedVersio

Iodine and Mercury Content in Raw, Boiled, Pan-Fried, and Oven-Baked Atlantic Cod (Gadus morhua)

There is a lack of scientific evidence regarding the stability of iodine and mercury during cooking and processing of seafood. In this study, the iodine and mercury content were determined after thawing frozen fillets of Atlantic cod (Cadus morhua), and further in raw compared to boiled, pan-fried, and oven baked fillets. Iodine was determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and mercury by atomic absorption spectrophotometry with Direct Mercury Analyzer (DMA-80). Thawing of the cod resulted on average in a 12% loss of iodine to the thawing water. Boiling significantly decreased the total content of iodine per slice of cod fillet corresponding to the concentration of iodine found in the boiling water. Pan-frying and oven-baking did not cause any significant changes of the total iodine content per slice of cod fillet, although iodine content per 100 g increased due to weight reduction of the cod slices from evaporation of water during preparation. For mercury, we found minimal changes of the different cooking methods. In summary, the findings in our study show that boiling had the greatest effect on the iodine content in the cod fillets. Type of cooking method should be specified in food composition databases as this in turn may influence estimation of iodine intake.publishedVersio

Weeks in Pregnancy on Maternal Iodine Status and Infant Neurodevelopment: Mommy's Food, a Randomized-Controlled Trial

Background: Mild-to-moderate iodine deficiency is still present in many countries, particularly in pregnant women. Observational studies suggest that mild-to-moderate iodine deficiency during pregnancy may be associated with impaired thyroid function and child neurodevelopment. Randomized-controlled food trials to increase iodine status are scarce. We assessed the impact of an increased intake of cod during pregnancy on maternal iodine status and infant neurodevelopment. Methods: In this randomized-controlled trial, pregnant women in Bergen, Norway, recruited through Haukeland University Hospital, were randomly assigned (1:1) to an intervention of 200 g of cod twice a week for 16 weeks (gestational week 20–36) or to continue with their standard diet (control group). Randomization was done by lottery. Primary outcome was urinary iodine concentration (UIC) (spot samples from six consecutive days) measured postintervention. Secondary outcome was infant neurodevelopment assessed by the cognitive, language, and motor scales of the Bayley Scales of Infant and Toddler Developmental third edition (Bayley-III) at 11 months of age. In addition, maternal thyroid function was measured (thyrotropin [TSH], free triiodothyronine [fT3], free thyroxine [fT4]) at baseline and postintervention. Results: Between January 2016 until February 2017, 137 women were recruited. Postintervention UIC was higher in the intervention group (n = 61) [median (interquartile range, IQR) 98 (64–145) μg/L], compared with control (n = 61) [median (IQR) 73 (52–120) μg/L] (p = 0.028), also after adjusting for baseline UIC (p = 0.048). Infants of mothers in the intervention group had a lower cognitive composite score on the Bayley-III compared with the control group (p = 0.045). There were no group differences in the Bayley III language- or motor composite scores. Maternal thyroid hormones (TSH, fT3, fT4) did not differ between the groups postintervention. Conclusions: Increased cod intake during pregnancy improved the iodine status in women with mild-to-moderate iodine deficiency, however, did not affect thyroid function. The negative effect on cognition should be followed up to assess whether this is a stable effect over time. More studies are warranted to enable good health advice on iodine nutrition in pregnancy. ClinicalTrials.gov NCT02610959. Registered November 20, 2015.publishedVersio

New data on nutrient composition in large selection of commercially available seafood products and its impact on micronutrient intake

Background: Most foods, including seafood, undergo some sort of processing as an integrated part of the global food industry. The degree of processing depends on the type of product produced. Processed seafood products are an important part of the diet; thus, knowledge of nutrient content in seafood products is of great importance. Objective: The aim of this study was to describe the content of selected nutrients in commercially available and market representative seafood products purchased from 3 different years. Methods: Seafood products from 2015 (n = 16), 2017 (n = 35), and 2018 (n = 35) were analyzed as composite samples for macro- and micronutrients using accredited methods at the Institute of Marine Research in Norway. Results: This study confirms that seafood products are good sources of several key nutrients, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), vitamin D, vitamin B12, iodine, and selenium. Fatty fish products had the highest content of EPA, DHA, and vitamin D, while lean fish products had the highest content of vitamin B12 and minerals. However, some lean fish products, such as one portion of fish au gratin or fish cakes, also proved as good sources of EPA, DHA, and vitamin D, and contributed substantially to the recommended intake. Variations in nutrients were seen both within the same product category and between the same product category from different years. Conclusions: These data give valuable insights into seafood products as a source of essential micronutrients and highlight the importance of these products for nutrition and health.publishedVersio

Effects of seafood consumption on mercury exposure in Norwegian pregnant women: a randomized controlled trial

Seafood provides nutrients that are important for optimal development of the unborn child. However, seafood is also a source of contaminants including mercury (Hg) and methylmercury (MeHg) that may have adverse effects on neurodevelopment of the fetus. Humans are predominantly exposed to MeHg through seafood consumption, however, levels of MeHg vary considerably between species.publishedVersio

Iodine Nutrition and Iodine Supplement Initiation in Association with Thyroid Function in Mildly-to-Moderately Iodine-Deficient Pregnant and Postpartum Women

Background Whereas the adverse effects of severe iodine deficiency during pregnancy are well documented, the effects of mild-to-moderate deficiency are not well established. Objectives We aimed to explore whether iodine nutrition and timing of iodine supplement initiation are associated with thyroid function in pregnant and postpartum women. Methods In this cohort study, 137 pregnant women were enrolled and followed up at gestational weeks (GWs) 18 and 36, and 3 and 6 mo postpartum. Thyroid function tests [thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), and free thyroxine (fT4)], urinary iodine and creatinine concentration (UIC:Cr), and iodine intake (including iodine supplement use) were measured at each time point. The associations between thyroid hormone concentrations and UIC:Cr, iodine intakes, and iodine supplement use were estimated using multiple generalized estimating equation models. Results The median UIC at GW18 was 94 μg/L, indicating mild-to-moderate iodine deficiency. UIC:Cr (β; 95% CI) per 100 μg/g was negatively associated with fT3 (−0.191; −0.331, −0.051) and fT4 (−0.756; −1.372, −0.141) concentrations. Iodine intake (β; 95% CI) per 100 μg/d was positively associated with TSH (0.099; 0.022, 0.177), and negatively associated with fT3 (−0.084; −0.0141, −0.027) and fT4 (−0.390; −0.599, −0.182) concentrations. Compared with no use of supplement, those initiating an iodine-containing supplement prepregnancy and continuing through pregnancy had lower TSH (estimated means) (1.35 compared with 1.68 mIU/L, P = 0.021), and higher fT3 (4.48 compared with 4.28 pmol/L, P = 0.035) and fT4 (15.2 compared with 14.4 pmol/L, P = 0.024) concentrations. Conclusions Lower iodine availability during pregnancy and postpartum was associated with lower TSH, and higher fT3 and fT4 concentrations. The use of an iodine-containing supplement that was initiated prepregnancy and continuing through pregnancy was associated with lower TSH, and higher fT3 and fT4 concentrations, which may suggest improved thyroid function. These findings support the notion that optimization of iodine intake should start before pregnancy. This trial was registered at clinicaltrials.gov as NCT02610959.publishedVersio

Infant iodine status and associations with maternal iodine nutrition, breastfeeding status and thyroid function

Adequate iodine nutrition during infancy is required for normal thyroid function and, subsequently, brain development. However, data on infant iodine status in the first year of life are scarce. This study aimed to describe infant iodine status and further explore its associations with maternal iodine nutrition, breast-feeding status and thyroid function. In this cohort study, 113 infants were followed up at ages 3, 6 and 11 months in Norway. Infant and maternal urinary iodine concentration (UIC), maternal iodine intake, breast milk iodine concentration (BMIC), breast-feeding status and infant thyroid function tests were measured. The median infant UIC was 82 µg/l at the age of 3 months and below the WHO cut-off of 100 µg/l. Infant UIC was adequate later in infancy (median 110 µg/l at ages 6 and 11 months). Infant UIC was associated positively with maternal UIC (β = 0·33, 95 % CI (0·12, 0·54)), maternal iodine intake (β = 0·30, 95 % CI (0·18, 0·42)) and BMIC (β = 0·46, 95 % CI (0·13, 0·79)). Breastfed infants had lower median UIC compared with formula-fed infants at ages 3 months (76 v. 190 µg/l) and 6 months (105 v. 315 µg/l). Neither infant UIC nor BMIC were associated with infant thyroid function tests. In conclusion, breastfed infants in Norway are at risk of insufficient iodine intake during the first months of life. Maternal iodine nutrition is important for providing sufficient iodine intake in infants, and awareness of promoting adequate iodine nutrition for lactating women should be prioritised.publishedVersio

Maternal and infant iodine nutrition and thyroid function : A cohort study of pregnant and postpartum women and their infants in Norway

Background: Iodine is a micronutrient essential for the production of the thyroid hormones. The thyroid hormones are particularly important for neurodevelopment of the foetus during pregnancy and for the developing child in the first years of life. Whereas the adverse effects of severe iodine deficiency are well documented, the consequences of mild-to-moderate iodine deficiency during pregnancy and infancy are still uncertain and data are limited. Objectives: The main objective of this thesis was to describe iodine nutrition and thyroid function and to explore associations between them in a cohort study of pregnant and postpartum women and their infants. The specific objectives were to: I) Assess the validity and reproducibility of an iodine-specific food frequency questionnaire (I-FFQ) developed for pregnant women. II) Explore whether iodine nutrition and timing of iodine supplement initiation were associated with altered thyroid function in mildly-to-moderately iodine-deficient pregnant and postpartum women. III) Describe infant iodine status and thyroid function and further explore associations between them in the first year of life. In addition, assess the impact of maternal iodine nutrition and breastfeeding status on infant iodine status. Methods: A total of 137 pregnant women were enrolled and followed-up at gestational weeks (GW) 18 and 36, and further with their infants at 3, 6 and 11 months postpartum. Dietary iodine intake from an I-FFQ and a six-day food diary, urinary iodine and creatinine concentrations (UIC and UIC:Cr), breast milk iodine concentration (BMIC) and thyroid function tests (thyroid-stimulating hormone (TSH), free triiodothyronine (fT3) and free thyroxine (fT4)) were measured. Results: Maternal iodine intake estimated from the I-FFQ showed acceptable correlation and agreement with iodine intake estimated from the six-day food diary and UIC, indicating that the I-FFQ can be used as a tool to estimate and rank iodine intake in this population. The median maternal UIC was below 100 µg/L during pregnancy (GW18: 94 µg/L; GW 36: 85 µg/L) and in the postpartum period (3 months: 74 µg/L; 6 months: 84 µg/L), indicating mild-to-moderate iodine deficiency of the mothers. The median infant UIC was 82 µg/L at age 3 months, thus, below the recommended WHO cut-off (100 µg/L), also indicating insufficient iodine status. Median infant UIC increased during the first year of life and was 110 µg/L at ages 6 and 11 months, indicating adequate iodine status at these ages. Infant UIC was associated with maternal iodine intake, UIC:Cr and BMIC. At ages 3 and 6 months, breastfed infants had a lower median UIC (76 and 105 µg/L, respectively) compared with formula-fed infants (190 and 315 µg/L, respectively). At age 11 months, no differences between breastfeeding categories were found. The prevalence of maternal and infant thyroid dysfunction in this study population was low. Lower maternal iodine availability (measured by iodine intake and UIC:Cr) was associated with higher fT3 and fT4 concentrations, and lower TSH concentrations (intake only). Compared with no use of supplements, those initiating an iodine-containing supplement before conception and continuing through pregnancy had lower TSH, and higher fT3 and fT4 concentrations. No associations were found between infant UIC nor BMIC with infant thyroid function (TSH, fT3, fT4). Conclusion: Pregnant and postpartum women and breastfed infants in their first months of life are at risk of iodine deficiency in Norway. No associations were found between infant iodine status and thyroid function. Maternal iodine nutrition was, however, associated with altered thyroid function tests, and initiation of iodine supplementation before conception and continuing through pregnancy was associated with possible improved thyroid function. Overall, to ensure normal thyroid function in the developing foetus and growing infant, maternal iodine nutrition should be optimised before conception and continued throughout pregnancy and the postpartum period. Awareness of promoting adequate iodine nutrition for these vulnerable population groups should be prioritised to secure sufficient iodine intake for mothers and, subsequently, their infants