Abstract
IntroductionIodine is a crucial component of thyroid hormones and is essential for foetal neuro-development. Iodine deficiency is the leading cause of preventable developmental delay globally, and the most common cause of thyroid dysfunction, particularly hypothyroidism. Since the recommendation from the World Health Organization to implement salt iodisation, iodine status throughout the world has improved. How-ever, high-income countries, including the UK, which does not currently have a programme of iodine fortification, have reported the re-emergence of mild-to-moderate iodine deficiency, particularly among pregnant women who have 50% higher iodine requirements than the general population.
Iodine deficiency has been reported among pregnant women in Northern Ireland. Due to the lack of salt iodisation or other iodine fortification within the UK and Ire-land, women are reliant on dietary sources, primarily dairy products for their iodine intake. At present, iodine supplementation is not recommended perinatally in the UK, despite the recommendation from organisations such as the American and European Thyroid Association.
Iodine knowledge has been shown to be poor among women and healthcare professionals around the world, but little is known about what the situation is in the UK or how this situation could be improved. Meanwhile, countries around the world have reported an increase in the incidence of congenital hypothyroidism with some suggesting this could be related to the re-emergence of iodine deficiency.
This thesis aims to explore if a dietary intervention study using dairy products can improve iodine status, if the provision of written information on iodine improves iodine nutrition and iodine knowledge, women’s experience of nutrition counsel-ling in pregnancy, what barriers midwives face when providing nutrition counselling and finally, to examine if the incidence of congenital hypothyroidism has changed over the past 40 years in Northern Ireland.
Methods
Women from one centre in Northern Ireland were recruited at their booking clinic appointment to the randomised dietary intervention. Following stratification, de-pending on verbal reporting of iodine-containing multivitamin use, a block randomisation schedule was used to allocate participants to the intervention or control group. Women in the intervention group received a 12-week supply of dairy products: semi-skimmed milk, low-fat yoghurt, or a combination of both.
Blood and urine samples were collected at recruitment along with the completion of demographic, iodine-specific food frequency and iodine knowledge questionnaires, and a four-day food diary. Further urine samples and food frequency questionnaires were completed after the 12-week intervention period, in the third trimester and 6-12 weeks postnatally, when a urine sample from the infant was also collected, along with a repeat iodine knowledge questionnaire and four-day food diary.
Pregnant women were invited to participate in a qualitative interview study exploring their experience of nutrition counselling during pregnancy. In tandem, midwives and midwifery academics around the UK were invited to participate in a qualitative study using semi-structured interviews to examine their experience of nutrition in midwifery undergraduate education, the delivery of nutrition counselling during clinical care, and barriers to this, and how they could be better supported to pro-vide nutrition counselling to patients.
A separate retrospective review of cases of congenital hypothyroidism detected through the newborn screening programme in Northern Ireland was performed using records stored at the Royal Belfast Hospital for Sick Children since the programme began in 1980.
Results
The randomised dietary intervention study included 118 women recruited at a mean gestational age of 12 weeks. The median urinary iodine concentration (mUIC) was 53.2 µg/L at recruitment. Those reporting use of an iodine-containing multi-vitamin (71.4% in this cohort) had a higher mUIC, 66.0 µg/L compared with 37.1 µg/L, but remained iodine deficient, defined as mUIC <150 µg/L. After a 12-week intervention period, those in the intervention group did not have significantly higher mUIC and remained iodine deficient, mUIC 120.7 µg/L in the intervention group compared with 105.7 µg/L in the control group (p=0.4). However, the mean change in mUIC in the intervention group was 88 µg/L compared to 44 µg/L in the control group (p=). The mUIC in both groups remained iodine deficient in the third trimester (whole cohort mUIC 85.2 µg/L) and post-natal period (whole cohort mUIC 62.0 µg/L), without significant differences.
There were no significant differences in anthropomorphic measurements at delivery. Urine sampling was achieved in 55 infants. Infants were iodine sufficient at 6-12 weeks post-natal with mUIC 124.1 µg/L with sufficiency in this group defined as mUIC >100 µg/L. There was no significant difference in the mUIC of infants born to mother in the intervention group.
Food frequency questionnaires showed that intake of dairy products did increase during the intervention period but did not reach the levels expected. While data from four-day food diaries showed lower than required iodine intake in women not using an iodine containing multivitamin. An iodine knowledge survey at the start of study found that 20.9% of women were able to identify iodine-rich foods, including milk, and confidence to achieve the required iodine intake was low, with most participants rating 0-5 on a Likert scale where 0 was no confidence at all and 10 was extremely confident. Only 39% of participants reported that they were aware that iodine requirements increased in pregnancy. At the end of study, 46 participants completed the same questionnaire with 67% reporting an awareness of increased iodine requirements, while recognition of dietary iodine sources remained poor.
Six women completed a semi-structured interview in the post-natal period. They reported a desire for more personalised information on diet and nutrition provided by healthcare professionals, associated with a willingness to change behaviour during pregnancy if the reasons and potential benefits were explained. All women in this cohort reported using an iodine-containing multivitamin although none reported being provided with information on iodine nutrition during routine antenatal care.
Midwives remain the main source of nutrition information during pregnancy, but in this cohort of ten midwives and midwifery academics from across the UK, knowledge of iodine nutrition was poor, and nutrition counselling was not a priority during midwifery education, and this was reflected in clinical consultations. The focus was primarily on delivery key safety messages on foods to avoid during pregnancy and to recommend use of a pregnancy-specific multivitamin. Barriers reported included time in the clinical consultation, lack of knowledge and lack of guidance.
In addition, incidence of congenital hypothyroidism in Northern Ireland has in-creased over the past 40 years from 26 per 100,000 live births in 1981-1990 to 73 per 100,000 live births in 2011-2020 (p<0.001). This was not clearly associated with an increase in the number of premature births or a significant change in the ethnicity of the population.
Conclusions
Women in one centre in Northern Ireland remained iodine deficient during pregnancy despite 71.4% reporting use of an iodine-containing pregnancy multivitamin. Following dietary intervention, there was no significant improvement in iodine nutrition status. Women’s knowledge of iodine was low, with little confidence to achieve sufficient iodine intake and few able to identify iodine rich foods.
The possible link between iodine knowledge and iodine nutrition status means this lack of knowledge may put women at increased risk of iodine deficiency in the al-ready precarious setting in the UK without iodine fortification. This is potentially exacerbated by a lack of iodine knowledge among healthcare professionals, and priorities in clinical care eclipsing the need for accurate, personal and implementable nutrition advice.
In Northern Ireland, there has been an increase in the incidence of congenital hypothyroidism over the past forty years. Although the underlying mechanism is un-clear and is likely multifactorial. One possible contributory factor is the re-emergence of iodine deficiency which has been demonstrated in this and a previous cohort in Northern Ireland.
These different elements of this thesis come together to highlight the need to prioritise iodine nutrition, given the persistent iodine deficiency during pregnancy, despite increased intake of dairy products, and consumption of an iodine-containing multivitamin, the need to consider fortification at a population is becoming compelling. Furthermore, the integration of nutrition education in healthcare professional undergraduate curricula should ensure the importance and relevance of nutrition is clear as well as equipping future healthcare professionals to counsel patients to make behavioural change.
Date of Award | Jul 2025 |
---|---|
Original language | English |
Awarding Institution |
|
Sponsors | Health and Social Care (Northern Ireland) Research and Development |
Supervisor | Michelle McKinley (Supervisor), Jayne Woodside (Supervisor) & Karen Mullan (Supervisor) |
Keywords
- Iodine
- pregnancy
- thyroid
- midwives
- congenital hypothyroidism