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Inadequate iodine intake is associated with subfecundity in mild-to-moderately iodine deficient Norwegian women
- Anne Lise Brantsaeter, Marianne H. Abel, Ida H. Caspersen, Verena Sengpiel, Bo Jacobsson, Per M. Magnus, Jan Alexander, Helle Margrete Meltzer
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- Journal:
- Proceedings of the Nutrition Society / Volume 79 / Issue OCE2 / 2020
- Published online by Cambridge University Press:
- 10 June 2020, E112
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Iodine is an essential micronutrient and an integral part of the thyroid hormones. In women of childbearing age, the estimated average iodine requirement is 95 μg/day and the recommended daily intake is 150 μg/day. While severe iodine deficiency poses reproductive risks, including infertility and abortions, the potential impact of mild-to-moderate iodine deficiency on subfecundity is unknown.
We examined whether iodine intake was associated with risk of subfecundity (i.e. > 12 months trying to get pregnant) in a large cohort of mild-to-moderately iodine deficient women.
Women enrolled in the Norwegian Mother and Child Cohort Study in gestational week 15 were asked to report whether the pregnancy was planned and how many months the couple had sexual relations without any contraception before getting pregnant. Information about time to pregnancy, maternal characteristics and iodine intake was available for 56,416 planned pregnancies. The median (interquartile range) time to pregnancy was 1.5 (0.5–6.0) months and the prevalence of subfecundity was 10.8%). We used iodine intake assessed by a validated food frequency questionnaire administered in pregnancy as a proxy for long-term (pre-pregnancy) iodine intake. We used logistic regression to estimate the association between iodine intake and subfecundity, using flexible modelling with restricted cubic splines, and adjusted for maternal age, BMI, parity, education, smoking status, energy intake and fiber intake. The median calculated iodine intake was 121 μg/day and the median urinary iodine concentration in a subsample of n = 2795 women was 69 μg/L.
The prevalence of subfecundity was lowest for iodine intakes ~100 μg/day and increased at lower intakes (p overall = 0.005). Compared to an intake of 100 μg/day (reference), intakes ~75 μg/day was associated with 5% (95%CI: 1%, 9%) higher prevalence and intakes ~50 μg/day with 14% (95%CI: 4%, 26%) higher prevalence. Use of dietary supplements was recorded only for the last 6 months prior to conception and women were included in the analysis regardless of their reported supplement use. In a sensitivity analysis, we excluding women who reported iodine-containing supplement use in the period 26–9 weeks before conception and the result remained unchanged. We also modelled time to pregnancy by Cox regression, and the result was consistent with the result for subfecundity.
The only good dietary sources of iodine in Norway are milk and white fish, and many women of fertile age have low intakes of these food items. This study shows that low habitual iodine intake may be a risk factor for subfecundity.
Mild-to-moderate iodine deficiency is associated with lower birthweight and increased risk of preterm delivery in a large Norwegian pregnancy cohort
- Marianne H. Abel, Ida H. Caspersen, Verena Sengpiel, Bo Jacobsson, Per M. Magnus, Jan Alexander, Helle Margrete Meltzer, Anne Lise Brantsaeter
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- Journal:
- Proceedings of the Nutrition Society / Volume 79 / Issue OCE2 / 2020
- Published online by Cambridge University Press:
- 10 June 2020, E409
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- Article
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- You have access Access
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Iodine is essential in foetal development through being an integral part of the thyroid hormones. Severe iodine deficiency is associated with foetal growth restriction and preterm delivery. Less is known about the potential impact of mild-to-moderate iodine deficiency on these outcomes.
The aim of this study was to investigate whether maternal iodine intake in pregnancy was associated with birth weight (BW) z-score (i.e. BW adjusted for gestational length and sex) and preterm delivery (before week 37).
The study population included 77,995 singleton pregnancies from The Norwegian Mother and Child Cohort Study recruited in gestational week 15 in the period 2002–2008. Habitual iodine intake was calculated from a validated food frequency questionnaire covering the first half of pregnancy. Use of supplements was reported in questionnaires. Urinary iodine concentration (UIC) was measured in gestational week 18 in a subsample of n = 2795 women. Median iodine intake from food was 121 μg/day and median UIC was 69 μg/L. Median UIC < 150 μg/L is considered insufficient in pregnant women. Median birthweight was 3610 g and 5.0% were born before gestational week 37. Associations were modelled flexibly by use of restricted cubic splines, and adjusted for age, parity, pre-pregnancy BMI, education, smoking in pregnancy, energy intake, and fibre intake.
In non-users of iodine-containing supplements (n = 48,958), a low habitual iodine intake from food (lower than about 150 μg/day) was associated with a lower mean BW z-score (p < 0.001). Compared to an intake of 150 μg/day (reference), mean z-score was 0.04 SD lower at 100 μg/day and 0.12 SD lower at 75 μg/day. Results were similar when using UIC as the exposure (n = 2795, p = 0.017). Any use of iodine containing supplements in pregnancy was associated with 0.03 (95% CI: 0.01, 0.04) SD increase in BW z-score compared to no use (n = 77,949, p < 0.001).
A low habitual iodine intake from food (lower than about 100 μg/day) was associated with increased risk of preterm delivery (p = 0.003). Compared to an intake of 100 μg/day (reference), 75 μg/day was associated with 10% increased risk, and 50 μg/day with 28% increased risk. Use of an iodine-containing supplement was not associated with the risk of preterm delivery (OR: 0.97 (95%CI: 0.91, 1.04, p = 0.42)).
Inadequate iodine intake is prevalent in women of childbearing age in otherwise well-nourished populations. Our results indicate that mild-to-moderate iodine deficiency in pregnancy is associated with restricted foetal growth and increased risk of preterm delivery.
Contributors
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- By Robert S. Anderson, (Mary) Colleen Bhalla, Michelle Blanda, Christopher Carpenter, Chris Chauhan, Paul L. DeSandre, Maura Dickinson, Jonathan A. Edlow, Dany Elsayegh, Kara Iskyan Geren, Peter J. Gruber, Jin H. Han, Marianne Haughey, Teresita M. Hogan, Ula Hwang, Lindsay Jin, Michael P. Jones, Joseph H. Kahn, Keli M. Kwok, Denise Law, Megan M. Leo, Stephen Y. Liang, Judith A. Linden, Brendan G. Magauran Jr, Joseph P. Martinez, Amal Mattu, Karen M. May, Aileen McCabe, Kerry K. McCabe, Jolion McGreevy, Ron Medzon, Ravi K. Murthy, Aneesh T. Narang, Lauren M. Nentwich, David E. Newman-Toker, Jonathan S. Olshaker, Joseph R. Pare, Thomas Perera, Joanna Piechniczek-Buczek, Jesse M. Pines, Timothy Platts-Mills, Suzanne Michelle Rhodes, Lynne Rosenberg, Mark Rosenberg, Todd C. Rothenhaus, Kristine Samson, Arthur B. Sanders, Jeffrey I. Schneider, Rishi Sikka, Kirk A. Stiffler, Morsal R. Tahouni, Mary E. Tanski, Abel Wakai, Scott T. Wilber, Deborah R. Wong
- Edited by Joseph H. Kahn, Brendan G. Magauran, Jr, Jonathan S. Olshaker
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- Book:
- Geriatric Emergency Medicine
- Published online:
- 05 January 2014
- Print publication:
- 16 January 2014, pp vii-x
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