Assessment of iodine status of lactating women and infants in Shanghai, China

doi:10.21203/rs.3.rs-1951620/v1

Download PDF

Research Article

Assessment of iodine status of lactating women and infants in Shanghai, China

https://doi.org/10.21203/rs.3.rs-1951620/v1

This work is licensed under a CC BY 4.0 License

Journal Publication

published 01 Mar, 2023

Read the published version in Biological Trace Element Research →

You are reading this latest preprint version

There is a risk of iodine deficiency in pregnant women in China. However, currently, little research is available on the iodine status of lactating women and infants. This study aimed to evaluate the iodine status of lactating women and their infants and explore the relationship between breast milk iodine concentration (BMIC) and urinary iodine concentration (UIC). 257 lactating women and their infants were recruited from the Shanghai Sixth People’s Hospital East campus between May 2018 and May 2019. BMIC and UIC were measured by inductively coupled plasma mass spectrometry (ICP-MS). One-day 24-hour dietary recall was used to determine the dietary intake of iodine. The mean dietary intake of iodine of the lactating women was 145.1 µg/day. The dietary iodine intake of 97.83% (n=225) of lactating women was lower than 240 µg/day. The median BMIC and UIC of the lactating women and UIC of the infants were 150.7 µg/L (Interquartile Range, IQR 102.9, 205.5), 110.0 µg/L (IQR 65.8, 171.4) and 212.7 µg/L (IQR 142.1, 320.6), respectively. The BMIC of lactating women who ate iodized salt was significantly higher than that without iodized salt (p = 0.015). The infants’ UIC values were significantly correlated with the BMIC values (r = 0.597^**, p < 0.001). The iodine nutritional status of lactating women and infants in Shanghai was generally sufficient according to the WHO's iodine nutritional status. The use of iodized salt was related to increasing dietary iodine intake and BMIC. The improvement of BMIC has a positive effect on the iodine nutrition level of infants. Compared with the level of urinary iodine of mothers, BMIC was a more sensitive and stable index to evaluate the iodine nutritional status of infants.

urinary iodine concentration

breast milk iodine concentration

lactating women

infants

dietary survey

Iodine is an essential micronutrient for fetal and infant brain development from the beginning of pregnancy to 2 years after birth [1]. Iodine deficiency can lead to irreversible body and brain damage during the critical period of infant brain development [2]. Approximately 40% ~ 45% of the iodine intake is transported into breast milk by the breast cells through the Na⁺/I⁻ symporter (NIS) and pendrin and iodine are preferentially provided to the infants during lactation. It suggested that a lower urinary iodine excretion than the breast milk iodine concentration (BMIC) of lactating women might cause iodine deficiency [3]. Iodine in breast milk is the only source of iodine intake for exclusively breastfed infants. Therefore, it is necessary to pay special attention to the intake of adequate dietary iodine on lactating women of the growth and development of their offspring. The Chinese Nutrition Society proposes recommended that nutrient intake (RNI) of iodine for lactating women is 240 µg/day and the World Health Organization (WHO) proposes 250 µg/day [4, 5]. In 2007, WHO guided for the assessment of iodine deficiency disorders in lactating women and children < 2 years of age, a median urinary iodine concentration (UIC) ≥ 100 µg/L on a population level was regarded as sufficient [5]. About 1.9 billion people (30% of the world’s population) were iodine deficiency worldwide[5]. Europe and Southeast Asia are most seriously affected by iodine deficiency[5].

China become one of the countries that have a strong impact on iodine deficiency due to distribution characteristics of iodine in nature. Long-term iodine deficiency led to iodine deficiency disorders (IDD). The primary prevention and treatment measure of IDD is salt iodization. In 1994, China implemented the Regulations on Edible Salt Iodization as a Means to eliminate iodine deficiency disorders to eliminate IDD. Although in 1995 China implemented the Universal salt iodization (USI) action, by 2000 it eliminated IDD at the national level[6]. Based on statistics results, the 20.4% of prevalence of endemic goitre in children aged 8 ~ 10 years decreased to 2.4% from 1995 to 2011 in China [7]. Among them, Shanghai, the largest coastal city and an iodine-sufficient area, is located in China [8, 9]. The iodized salt coverage rate of Shanghai residents was over 90% from 2002 to 2012. Since 2010, the iodized salt coverage rate of Shanghai residents decreased year by year, and the non-iodized salt coverage rate of residents reached 20.91% in 2015 [10]. The previous study showed that the median UIC of lactating women in Shanghai was 131.1 µg/L in 2009 ^[9]. In 2011, the national monitoring of iodine deficiency disorders showed that the median UIC of lactating women in Shanghai was 123.1 µg/L [10]. Although lactating women's iodine nutritional status in Shanghai was generally sufficient, the median UIC result showed a downward trend.

In our previous study, the daily consumption of regular iodized salt by 349 pregnant women was only 78.0%, and pregnant women in Shanghai had mild iodine deficiency [11]. It is worthy of further investigation whether lactating women and infants in Shanghai are also in iodine deficiency. Some studies investigated the BMIC and UIC of lactating women and infants. However, it is unclear whether the current iodine status in Shanghai is sufficient after the decrease in the iodized salt coverage rate. Therefore, the purpose of this study was to evaluate the iodine nutritional status of lactating women and their infants in Shanghai could be used as an index of adequate iodine status of lactating women. This work will provide new insights into the prevention of potential harm of iodine malnutrition and the encouragement of appropriate countermeasures in time.

2.1. Study design

This study was a cross-sectional analysis embedded. The cohort recruited 257 lactating women (18−40 years old) who were examined 42-day postpartum in the Shanghai Sixth People’s Hospital East campus and their infants between May 2018 and May 2019. The inclusion criteria were set as follows: generally healthy and singleton pregnancy have no history of clinical or subclinical thyroid and other autoimmune and endocrine diseases; they lived in the local area for more than three years and no migration soon; they are able to cooperate with the follow-up. Those who were currently using drugs and lotions containing iodine, or had a history of smoking or alcoholism of this study were not covered. Three women taking anti-thyroid drugs during pregnancy were excluded from the 257 participants.

2.2. Data and sample collection

During the 42-day postpartum follow-up, approximately 10 mL of breast milk samples and spot urine samples were collected from the lactating women, and 10 mL of spot urine samples were collected from the baby. Breast milk and urine samples were separately stored at − 80°C and − 20°C, respectively, before use. Maternal age, height, weight (42 days after delivery, intrapartum and pre-pregnancy), education, gestational age and delivery mode were collected by questionnaires. Infant data regarding age, sex, birth and 42-day weight, type of feeding and brand of infant formula were also collected by questionnaires. Food consumption and dietary supplements on the day before urine sample collection were collected via 24-hour dietary recall. Trained investigators interviewed the participants face to face about the type and amount of food they ate. 48-hour after delivery, blood samples were collected from the heel of the newborn, and dried blood spots (DBS) were prepared.

2.3. Ethics

The Ethics Committee approved the study of Shanghai Sixth People’s Hospital East Campus (No.2016-003). The lactating women provided written consent and received written information about the study.

2.4. Laboratory analysis

UIC and BMIC were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) (Agilent 7700X; ICAP-Q, Thermo Fisher Scientific). Thyroid stimulating hormone (TSH) levels in neonatal heel blood were measured by time-resolved fluoroimmunoassay (TRFIA). Maternal TSH was measured by electrochemiluminescence. Roche, Germany, supplied the test kits.

2.5. Evaluation criteria of dietary iodine intake

According to the WHO, the recommended cooking loss rate of iodized salt is 20% [12], and the concentration of iodized salt in Shanghai is 30 mg/kg [13]. Dietary iodine intake mainly comes from food, drinking water and iodized salt, which was calculated according to the following formula:

Dietary iodine intake (µg/d) =∑(intake of various foods×Iodine content of various foods) + (drinking water + cooking food water)×Iodine content of water + salt intake×Iodine content of salt×(1 - cooking loss rate).

The dietary iodine intake was estimated using the Nutrition Star program (NS-Pro) premium version (ShangHai ZhenDing Health Science Technology Co., Ltd, Shanghai, 201306, China). The dietary iodine estimated average requirement (EAR) of lactating women is 170 µg/day, the RNI is 240 µg/day and the tolerable upper intake level (UL) is 600 µg/day [4].

2.6 Definitions

The adequate TSH of this study ranged from 0.1to 4.0mIU/L [14, 15]. A TSH upper reference limit (cut off) of 4.0 mIU/L has been proposed. In addition, the thyroid function of the population was diagnosed according to the guideline on diagnosis and management of thyroid diseases during pregnancy and postpartum [16].

The determination of TSH level in neonatal heel blood is considered as a most sensitive and reliable index to evaluate iodine nutrition level and thyroid function. In 2007, WHO/UNICEF/ICCIDD jointly recommended the cut-off point of neonatal TSH at 5.00 mIU/L, and the proportion of neonatal heel blood TSH > 5.00 mIU/L is less than 3% as the judgment standard of normal iodine nutritional status[5]. The standard range of neonatal TSH is 0.00 ~ 9.00 mIU/L.

In 2007, the WHO put forward an evaluation standard of iodine status based on the median UIC at a population level. The suitable standard of iodine nutrition level for breastfeeding women and infants younger than 2 years old is a median UIC > 100 µg/L [5].

Full-term infants need to take in 15 µg iodine per kg body weight per day to maintain a positive iodine balance, which is equivalent to a BMIC of 100 ~ 200 µg/L[17, 18].

2.7. Statistical analysis

All the analyses were performed using SPSS (SPSS Inc., Chicago, IL, United States, version 25).and p < 0.05 were used to significant differences. Data were presented as mean values and standard deviations (SD), numbers and percentages, or median and interquartile ranges (IQR) as appropriate. Spearman’s correlation analysis examined the correlations between BMIC and UI, between maternal BMIC and UIC, between maternal and infantile UIC, respectively. The Mann–Whitney U test was used to compare the differences between two data groups.

3.1 Characteristics of participants

There were 254 lactating women and their babies on data of lactating women and their infants(Table 1). The mean (± Standard Deviation, SD) age of the women at delivery and their infants (when tested) were 30.1 ± 4.1 years and 46.4 ± 5.3 days, respectively. The mean body weight of the women before pregnancy and before delivery were 55.8 ± 7.9 kg, 69.9 ± 8.5 kg, respectively. The average weight gain during pregnancy was 14.1 ± 4.9 kg. Infants gained 1.9 ± 0.54 kg in 42 days.

Table 1

Basic characteristics of infants and their mothers.
Characteristics	Value^*
Mothers
Sample size, n	254
Age (years)	30.1 ± 4.1
Gestational age (week)	39.1 ± 1.7
Height (cm)	161.1 ± 4.7
Pre-pregnancy weight (kg)	55.8 ± 7.9
Intrapartum weight (kg)	69.9 ± 8.5
42d after delivery weight (kg)	60.8 ± 8.6
Education
Secondary education or less	78(30.7)
Tertiary educated or above	161(63.4)
Education missing	15(5.9)
Delivery mode
Vaginal birth	150(59.1)
Cesarean section	104(40.9)
Feeding pattern
Breast-feeding	156(61.4)
Mixed feeding	82(32.3)
Pure milk powder feeding	16(6.3)
Infants
Sample size, n	254
Sex
Male	144(56.7)
Female	110(43.3)
Age (day)	46.4 ± 5.3
Birth length (cm)	50.2 ± 1.1
Birth weight (kg)	3.4 ± 0.5
42d weight (kg)	5.3 ± 0.7
Note:^*Data are means ± SD or n (%)

Of the mothers, approximately 63.4% had received tertiary education or above, and 59.1% underwent spontaneous delivery. In this survey, 61.4% of the infants were exclusively breastfed, and 6.3% were pure milk powder feeding.

The mean score for 42 d weight of breastfed infants, mixed fed infants and milk powder fed infants were 5.3 ± 0.7 kg, 5.2 ± 1.1 kg and 5.3 ± 0.7 kg, respectively. It suggested no significant difference in 42 d weight among infants with different feeding patterns (P = 0.840) (Kruskal Wallis Test).

3.2 UIC and BMIC of lactating women and UIC of infants

The median UIC was 110.0 µg/L (IQR 65.8, 171.4) for lactating women and 212.7 µg/L (IQR 142.1, 320.6) for infants. However, 44.5% of the women and 10.1% of the infants had iodine deficiency, with UIC values lower than the suggested cut-off level for adequacy of 100 µg/L. The median BMIC was 150.7 µg/L (IQR 102.9, 205.5), and 23.4% of the women had BMIC less than the suggested cut-off level for adequacy of 100 µg/L (Table 2, Fig. 1) [17].

Table 2

Iodine status in infants and their mothers.
	Mothers			Infants
	UIC (µg/L)	BMIC (µg/L)	dietary iodine intake (µg/d)	UIC (µg/L)
n	238	209	230	209
Median	110.0	150.7	151.3	212.7
IQR	65.8-171.4	102.9-205.5	136.0-170.1	142.1-320.6
UIC, urinary iodine concentration; BMIC, breast milk iodine concentration; IQR, interquartile range.

The median UIC was 211.4 µg/L (IQR 143.2, 346.3) for breastfed infants, 211.0 µg/L (IQR 106.1, 266.5) for mixed fed infants and 215.9 µg/L (IQR 147.1, 328.4) for milk powder fed infants. There was no significant difference in UIC among infants with different feeding methods (P = 0.578) (Kruskal Wallis Test).

The result of UIC of infants was significantly higher than that of lactating mothers when compared with UIC of exclusively breastfed infants, lactating mothers UIC and BMIC (P < 0.001). The BMIC of lactating mothers was significantly higher than their UIC (P < 0.001). The UIC of infants was significantly higher than that of lactating mothers (P < 0.001). The UIC of infants was the highest, followed by BMIC, and UIC of lactating mothers was the lowest. There was a significant difference between the three groups (P < 0.001).

This study analyzed the correlation among UIC of exclusively breastfed infants, UIC of lactating mothers and BMIC. The infants’ UIC values were significantly correlated with the BMIC values (r = 0.597^**, p < 0.001). The infants’ UIC values were weakly correlated with the maternal UIC values (r = 0.182^*, p = 0.01). The maternal UIC values were significantly correlated with the BMIC values (r = 0.373^**, p < 0.001) (Fig. 2).

3.3 Dietary iodine intake of lactating women

In the dietary study, a total of 230 lactating women completed their 24-hour dietary recalls, and their mean dietary iodine intake was 145.1 µg/day which was lower than the 240 µg/day recommended by the Chinese Nutrition Society (Table 2)[4]. The dietary iodine intake of 74.35% (n=171) lactating women was lower than 170 µg/day, 23.48% (n=54) was in the range of 170–240 µg/day, and 2.17% (n=5) was in the range of 240–400 µg/day.

The correlation between dietary iodine intake of lactating women and self UIC, BMIC and UIC levels of exclusively breastfed infants were investigated. The dietary iodine intake of lactating women was weakly positively correlated with their BMIC (r = 0.216^*, p = 0.014) and with infantile UIC (r = 0.205^*, p = 0.024). However, BMIC did not correlate with UIC.

Among the lactating women, 86.1% (n = 198) consumed iodized salt, 13.5% (n = 31) consumed non-iodized salt, and 0.4% (n = 1) consumed mixed salt. The mean dietary iodine intakes of the non-iodized salt and iodized salt groups were 31.5 µg/day and 155.9 µg/day. The median BMIC was 111.9 µg/L (IQR 68.7, 162.8) in the non-iodized salt group and 156.8 µg/L (IQR 115.8, 208.8) in the iodized salt group. Significant differences were observed between the iodized salt and non-iodized salt groups of lactating women in terms of dietary iodine intake (p < 0.001) and BMIC (p = 0.015), but not for their UIC (p = 0.307) or infantile UIC (p = 0.250) (Table 3).

Table 3

UIC, BMIC and dietary iodine intake of mothers and UIC of their infants by type of salt intake.
	Type of salt
	non-iodized salt		iodized salt
Variables	Median	IQR	Median	IQR	P^*
Mothers
UIC (µg/L)	107.6	54.8-151.6	111.8	70.2-173.4	0.307
BMIC (µg/L)	111.9	68.7-162.8	156.8	115.8-208.8	0.015
Dietary iodine intake (µg/d)	31.5	17.8–42.2	155.9	139.8-172.4	0.000
Infants
UIC (µg/L)	195.8	86.8-275.6	221.6	145.5-335.2	0.250
Note: UIC, urinary iodine concentration; BMIC, breast milk iodine concentration; IQR, interquartile range.
^*Mann–Whitney U test

3.4 Effect of TSH in the third trimester of pregnancy on TSH in heel blood of offspring

The median TSH of the neonates was 1.5 mIU/L (IQR 1.0, 2.3), which was within normal limits in all. The proportion of TSH > 5 mIU/L in heel blood of newborns is 0.5%, less than 3%, so the iodine nutritional status of newborns is normal [5].

The TSH level of lactating mothers in the third trimester of pregnancy was weakly correlated with the TSH in the heel blood of newborns level (r = 0.179^*). Meanwhile, based on the maternal TSH level in the third trimester of pregnancy, 233 pairs of mothers and infants were divided into two groups with TSH less than 4 mIU/L and TSH greater than 4 mIU/L to explore the relationship between maternal TSH in the third trimester of pregnancy and neonatal TSH. The median TSH of infants (TSH < 4 mIU/L) was 1.4 mIU/L (IQR 1.0, 2.1). However, the median TSH of infants (TSH > 4 mIU/L) in the group with was 2.2 mIU/L (IQR 1.4, 3.3). Interestingly, the TSH in the heel blood of infants in the group with TSH < 4 mIU/L in late pregnancy was lower than that in the group with TSH > 4 mIU/L in late pregnancy, and there was a significant difference (p = 0.031).

This study reports BMIC values, UIC values and dietary iodine intake for lactating women, and UIC values for infants in Shanghai, China. These results indicated that the iodine nutritional status of lactating women and infants in shanghai was sufficient based on the 2007 WHO criteria.

A Spanish study reported that the median UIC of lactating women was 142 µg/L from [19]. The median UIC of 380 lactating women in Shanghai in 2012, China, was 131.1 µg/L and 36.8% of the participants and had iodine deficiency of < 100 µg/L with a cross-sectional survey.

The previous study on iodine balance in infants at term reported that the iodine balance was positive only when the dietary iodine intake was 15 µg/kg per day, which was equivalent to a BMIC of 100 ~ 200 µg/L[17]. In our study, the median BMIC was 150.7 µg/L (IQR 102.9, 205.5), and 23.4% of women had BMIC less than the suggested cut-off level for adequacy. Western Australia, which has always been regarded as an iodine-rich region in Australia, has a median BMIC of 167 µg/L (IQR 99, 248), with 26% of lactating women having BMIC less than 100 µg/L [20, 21]. Korea is an iodine-replete country, with a median BMIC of 2529 (IQR 355, 8484), 1153 (IQR 198, 3791) and 822 (IQR 236, 1836) µg/L in the first, third and sixth weeks, respectively [22]. A study in Nepal collected 291 breast milk samples with a median BMIC of 250 µg/L (IQR 130, 370), and about 18% of the patients had BMIC < 100 µg/L [23]. Meanwhile, several research suggested that there was still a risk of low iodine intake among some mothers who adopted breastfeeding in areas with adequate iodine, and additional iodine supplementation was needed [20, 24]. Because of iodine content in milk is 2 ~ 3 times in plasma, which will accelerate consumption the more iodine from maternal lactation in the body. Breastfed infants rely on the iodine in breast milk to achieve their needs. The lack of iodine intake by mothers will decrease the iodine content in their breast milk, thus affecting the iodine nutrition of infants [25].

Our results showed that the UIC of lactating women was mainly distributed between 0 and 200 µg/L, the BMIC was mainly distributed between 100 and 200 µg/L, and the infant UIC was mainly distributed between 100 and 300 µg/L. There were significant differences in UIC of infants, BMIC and UIC among lactating women (P < 0.001). Lactating women had the lowest UIC, followed by BMIC, and infants had the highest UIC. It suggested that breast cells of lactating women could preferentially concentrate iodine from the blood to meet the needs of infants, to reduce their urinary excretion and the clearance rate of kidneys, to regulate the content of iodine in milk during lactation [26].

A weak correlation was found between maternal UIC and infantile UIC in this study. In different studies, a significant positive association has been found between maternal and infantile urinary iodine levels [26, 27]. In addition, the infants’ UIC values were significantly correlated with the BMIC values (r = 0.597^**, p < 0.001), and weakly associated with the maternal UIC values (r = 0.182^*, p = 0.01). Compared with the level of urinary iodine of mothers, BMIC was a more sensitive and stable index to evaluate the iodine nutritional status of infants. A significant positive correlation between BMIC and UIC in lactating women and their infants indicated that UIC in lactating women and their infant's changes parallel to BMIC. The previous study showed a positive correlation between the BMIC and UIC of lactating women, higher when adjusted for creatinine, which were similar to the results reported in our study[27]. Moreover, a significant positive correlation between BMIC and infant UIC was observed by the result of Wang et al.(2009) [28], which might conclude that the improvement of BMIC has a positive effect on the iodine nutrition level of infants.

EAR is an essential index to assess the iodine intake of groups and individuals. The iodine intake of groups is lower than EAR, which indicates that the proportion of people with iodine deficiency risk is up to 50%. The individual's iodine intake is lower than EAR, the risk of iodine deficiency can reach 50%suggesting needs improvement. When the intake increases to the RNI level, the probability of insufficient iodine intake of random individuals becomes very small, and the chance of iodine deficiency is less than 3%, while the average intake of a population reaches RNI, only 2% ~ 3% of the individuals may be deficient, that is, the vast majority of individuals are not at risk of iodine deficiency. The Chinese Nutrition Society proposes that the recommended nutrient intake (RNI) of iodine for lactating women is 240 µg/day, and the WHO recommends that the dietary iodine intake of lactating women is 250 µg/day [4, 5]. However, in our study on lactating women's mean dietary iodine intake in the Lingang area of Shanghai was 145.1 µg/day. The dietary iodine intake of 97.83% (n=225) of lactating women was lower than 240 µg/day, which was far lower than the suggested adequate cut-off, indicating that some lactating women might be at risk for iodine deficiency. According to the 24-hour meal review and dietary record evaluation, the current nutritional iodine intake of lactating women in Shanghai is insufficient. In 2017, a Spanish study found that the median nutritional iodine intake of lactating women was 125 µg/day (IQR 104, 154)[19]. Chinese residents' iodized salt consumption rate has continued to decline, and the iodized salt coverage rate in Shanghai has decreased to 16.91% from 2010 to 2015 [10]. In this survey, 86.1% of lactating women ate iodized salt, and the dietary iodine intake (p < 0.001) and BMIC (p = 0.015) of lactating women who ate iodized salt were significantly higher than in those who ate non-iodized salt and the difference was statistically significant. The use of iodized salt was related to increasing dietary iodine intake and BMIC. A recent study suggested that using either iodine-containing supplements or iodized salt had similar positive effects on the median BMIC, and both increased the iodine content of breast milk [20]. We also found a weakly positive correlation between dietary iodine intake and BMIC in lactating women (r = 0.216^*, p = 0.014).

Therefore, dietary iodine intake is a virtual indicator to improving milk iodine levels and infant iodine nutrition. Iodine is metabolized in the human body every day. When iodine intake stops, the iodine stored in the body is only enough to maintain for 2 ~ 3 months. Therefore, it is necessary to ensure sufficient dietary iodine intake every day. Although the iodine deficiency control program has been effectively maintained through salt iodization in China, the insufficient dietary iodine intake of lactating women is still a problem [7, 29, 30]. Therefore, some reasons for insufficient dietary iodine intake in lactating women may be as follows. First, mothers are worried that the high salt content in breast milk will affect the health of their infants in the early stage of breastfeeding, hence they reduce their intake of salt. Second, although Shanghai is a coastal city, the frequency and consumption of iodine-rich foods such as kelp and laver in local areas are low, and most of the iodine in residents' diet comes from iodized foods salt. Finally, the masses do not know enough about the harm of iodine deficiency, and the awareness of prevention and control is gradually weakened. An increasing amount of evidence revealed that lactating women should continue to increase the intake of dietary iodine during pregnancy. First, eating iodized salt and iodine-rich foods of kelp and laver can be used to consider supplement iodine [31]. In addition, iodine-containing nutrient supplements can also be considered.

When comparing the influence of maternal TSH level in the third trimester on infant TSH, it was found that the TSH in the heel blood of infants in the group with TSH < 4 mIU/L in late pregnancy was lower than that in the group with TSH > 4 mIU/L in late pregnancy, and there was a significant difference (p = 0.031). These results suggested that the abnormal TSH level of mothers in the third trimester of pregnancy in this region increased the risk of TSH level in their offspring. According to Korevaar T [32], there is a strong correlation between maternal TSH and newborn TSH, and newborn TSH level can be predicted by maternal TSH level, and the effect is good. When comparing the levels of TSH and the incidence of hypothyroidism in neonates in iodine-rich and iodine-deficient areas, it was found that the levels of TSH and the incidence of hypothyroidism were higher in iodine-deficient areas. Ji et al. studied the relationship between the TSH level of pregnant women with different iodine nutrition statuses and the newborn and found that when the mother was iodine deficient during pregnancy, the abnormal rate of TSH in the newborn was 3.28%, which was significantly higher than that of the infants born by iodine-suitable pregnant women (P < 0.05)[33]. These results indicated that the birth quality of newborns was closely related to the iodine nutritional status of pregnant women. The key role of adequate iodine intake of mothers is conducive to reducing the incidence of TSH abnormalities in offspring during pregnancy.

This study found that the iodine nutrition level of lactating women and infants in Shanghai is generally suitable, and relevant data for the Shanghai district are supplemented. Our research has the following limitations, which need to be further improved. First, we only collected single spot urine samples from each lactating woman and infant, which may not accurately reflect the iodine nutritional status of individuals. The ideal method is to use 24-hour urine iodine, but it is not easy to collect such samples from lactating women. We will try to overcome the above difficulty and collect 24-hour urine samples to measure the urinary iodine level in the future study. Second, this study only evaluated the iodine nutrition level of lactating women and infants in the Lingang district of Shanghai, and the results do not represent the entire city. Therefore, more attentions should be paid to generalizing the results of this study to other regions and populations. It should increase the sampling area and representativeness of the results.

In this study, the abnormal TSH in the mother in late pregnancy increased the risk of increased TSH in the heel blood of the offspring was found. We will follow up on the investigation of pregnant women in the Shanghai Sixth People’s Hospital East to explore the cause and authenticity of this finding. We will evaluate their iodine nutrition level, detect their thyroid hormone level, and explore the changing trends and relationships of these parameters during the first, second, third, and postpartum periods.

Our research has provided evidence to demonstrate that the iodine nutritional status of lactating women and infants in Shanghai is generally sufficient at the population level, but a large proportion of lactating women still have low daily dietary iodine intake. Therefore, we the prevention and monitoring of iodine deficiency disorders (IDD) in particular populations should be done to strengthen. It is an essential way to advocate scientific iodine supplementation and ensure the appropriate dietary iodine intake of lactating women to avoid the severe harm of IDD.

Acknowledgements

We would like to thank the lactating women and their children for participating in this study. We are also grateful to the Shanghai Sixth People’s Hospital East staff.

Conflicts of Interest

The authors declare that they have no conflict of interest.

Availability of data and material

The data used to support the findings of this study are available from the corresponding author upon request.

Funding

This research was supported by the Scientific Research Fund of the Shanghai Municipal Commission of Health and Family Planning and the Shanghai Municipal Health Commission (No. 201640250, 2019ZB0104).

Author Contribution

Wenguang Sun: Study design, critical revision of the article. Wenqing Yan: Data collection and analysis, drafting the article, writing-review and editing. Chunling Bao: performed clinical diagnosis and recruitment; Wenqing Yan and Wenxia Tian performed questionnaire and data collection. Xin-Yun Wang: writing-review, editing, critical revision of the article.

Zhang Y., Yu-Ying L. I., Yao X., et al., Iodine and thyroid diseases, Chinese Bulletin of Life Sciences, (2012).
Su H., Lian D., Wei C., Study on status of iodine nutrition of pregnant women in different gestation periods, Modern Journal of Integrated Traditional Chinese and Western Medicine, (2010).
Laurberg P., Andersen S. L., NUTRITION Breast milk-a gateway to iodine-dependent brain development, Nature Reviews Endocrinology, 11 (2014).
Nutrition C., Chinese dietary reference intakes, in, Science Press: Beijing, 2013.
Organization W. H., Assessment of iodine deficiency disorders and monitoring their elimination: a guide for programme managers, in, World Health Organization, 2001.
Codling K., Chen Z., Hongmei S., et al., China: leading the way in sustained IDD elimination: the international council for control of iodine deficiency disorders (ICCIDD) global network, IDD Newsl, 42 (2014) 1-5.
Sun D., Codling K., Chang S., et al., Eliminating iodine deficiency in China: achievements, challenges and global implications, Nutrients, 9 (2017) 361.
Zhen Y., Wang Q., Li Y., Investigation and analysis of iodine nutrition status of key population in Zhangye City and intervention measures, Health Vocational Education, 26 (2008) 103-105.
Zou S., Wu F., Guo C., et al., Iodine nutrition and the prevalence of thyroid disease after salt iodization: a cross-sectional survey in Shanghai, a coastal area in China, (2012).
ZANG J.-J., ZHOU J.-Z., ZOU S.-R., et al., Comprehensive assessment on iodine nutrition and dietary iodine intake among Shanghai residents, Shanghai Journal of Preventive Medicine, (2017) 417-422.
Tian W., Yan W., Liu Y., et al., The Status and Knowledge of Iodine among Pregnant Women in Shanghai, Biological Trace Element Research, 199 (2021) 4489-4497.
Unit N., Organization W. H., Recommended iodine levels in salt and guidelines for monitoring their adequacy and effectiveness, in, World Health Organization, 1996.
Zhang Y. W., Zhou G. J., Tong N. W., The classificatory prevention guidelines of atherosclerotic cerebral and cardiovascular diseases in chinese adults with diabetes, Chinese Journal of Practical Internal Medicine, (2016).
Stagnaro-Green A., Abalovich M., Alexander E., et al., Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and postpartum, Thyroid, 21 (2011) 1081-1125.
Zhang Y., Liu F., Sun W., et al., Establishment of reference ranges for thyroid-related indicators in normal pregnant women, Zhonghua yi xue za zhi, 96 (2016) 339-343.
Chen G.-d., Gou X.-Y., Pang T.-t., et al., Associations between thyroid function and gestational diabetes mellitus in Chinese pregnant women: a retrospective cohort study, BMC endocrine disorders, 22 (2022) 1-9.
Semba R. D., Delange F., Iodine in human milk: perspectives for infant health, Nutrition reviews, 59 (2001) 269-278.
Ares S., Quero J., de Escobar G. M., Neonatal iodine deficiency: clinical aspects, Journal of Pediatric Endocrinology and Metabolism, 18 (2005) 1257-1264.
Castilla A. M., Murcia M., Arrizabalaga J. J., et al., Comparison of urinary iodine levels in women of childbearing age during and after pregnancy, European journal of nutrition, 57 (2018) 1807-1816.
Jorgensen A., O’Leary P., James I., et al., Assessment of breast milk iodine concentrations in lactating women in Western Australia, Nutrients, 8 (2016) 699.
Li M., Ma G., Guttikonda K., et al., Re-emergence of iodine deficiency in Australia, Asia Pacific Journal of Clinical Nutrition, 10 (2001) 200-203.
Chung H. R., Shin C. H., Yang S. W., et al., Subclinical hypothyroidism in Korean preterm infants associated with high levels of iodine in breast milk, The Journal of Clinical Endocrinology & Metabolism, 94 (2009) 4444-4447.
Henjum S., Kjellevold M., Ulak M., et al., Iodine concentration in breastmilk and urine among lactating women of Bhaktapur, Nepal, Nutrients, 8 (2016) 255.
Isiklar Ozberk D., Kutlu R., Kilinc I., et al., Effects of mandatory salt iodization on breast milk, urinary iodine concentrations, and thyroid hormones: is iodine deficiency still a continuing problem?, Journal of endocrinological investigation, 42 (2019) 411-418.
Dror D. K., Allen L. H., Iodine in human milk: a systematic review, Advances in Nutrition, 9 (2018) 347S-357S.
ZHU Y., HUANG J., ZHANG R., et al., Effects of different iodine levels on thyroid function in rats after pregnancy, Chinese Journal of Endemiology, (2021) 689-693.
Kurtoglu S., Akcakus M., Kocaoglu C., et al., Iodine status remains critical in mother and infant in Central Anatolia (Kayseri) of Turkey, European Journal of Nutrition, 43 (2004) 297-303.
Wang Y., Zhang Z., Ge P., et al., Iodine status and thyroid function of pregnant, lactating women and infants (0-1 yr) residing in areas with an effective Universal Salt Iodization program, Asia Pacific journal of clinical nutrition, 18 (2009) 34-40.
Sun D., Liu P., SU X., A decade evolution of residents' iodine nutrition level in China, Chinese Journal of Endemiology, (2018) 1-3.
SU X., LIU P., SHEN H., et al., An interpretation of"" The Consensus of 2016 Conference on Iodine and Thyroid Disease"", Chinese Journal of Endemiology, (2017) 81-86.
Mao G., Ding G., Lou X., et al., Survey of iodine nutritional status in 2011, Zhejiang, China, Asia Pacific Journal of Clinical Nutrition, 24 (2015) 234-244.
Korevaar T. I., Chaker L., Jaddoe V. W., et al., Maternal and birth characteristics are determinants of offspring thyroid function, The Journal of Clinical Endocrinology, 101 (2016) 206-213.
Feng-Yu J. I., Han B., Yao-Hui X. U., Analysis of Iodine Nutritional Status of Pregnant Women in Baotou Area and Its Effect on Neonatal Heel Thyroid Hormone Levels, China & Foreign Medical Treatment, (2018).

No competing interests reported.

Download PDF

Journal Publication

published 01 Mar, 2023

Read the published version in Biological Trace Element Research →

Editorial decision: Major revision
27 Aug, 2022
Reviews received at journal
14 Aug, 2022
Reviewers agreed at journal
14 Aug, 2022
Reviewers invited by journal
13 Aug, 2022
Editor assigned by journal
12 Aug, 2022
Submission checks completed at journal
12 Aug, 2022
First submitted to journal
11 Aug, 2022

You are reading this latest preprint version

Assessment of iodine status of lactating women and infants in Shanghai, China

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Materials And Methods

2.1. Study design

2.2. Data and sample collection

2.3. Ethics

2.4. Laboratory analysis

2.5. Evaluation criteria of dietary iodine intake

2.6 Definitions

2.7. Statistical analysis

3. Results

3.1 Characteristics of participants

3.2 UIC and BMIC of lactating women and UIC of infants

3.3 Dietary iodine intake of lactating women

4. Discussion

5. Conclusion

Declarations

References

Additional Declarations

Status:

Journal Publication

Version 1