PFPC Fluoride Education Project

Griebel-Thompson A, Sands S, Chollet-Hinton L, Christifano D, Sullivan D, Hull H, Carlson S - "Iodine Status, Fluoride Exposure, and Thyroid Function in Pregnant Women in the United States" Current Developments in Nutrition 6(1):652 (2022) ABSTRACT ONLY
https://doi.org/10.1093/cdn/nzac061.036

Abstract

Objectives

Iodine (I) is an essential nutrient for fetal neurodevelopment through its role in thyroid function. Like I, fluoride (F) is a halogen and urinary F concentration (UFC) has been linked to increased thyroid stimulating hormone (TSH) in non-pregnant adults with I deficiency. We hypothesize that F and I may interact in their role on thyroid function among pregnant women.

Methods

Pregnant women (n = 966) provided urine between 12- and 20-weeks gestation. UIC was measured by the modified Sandell-Kolthoff reaction and UFC by a F-sensitive electrode. Enzyme-linked immunosorbent assay (ELISA) was used to measure plasma TSH. Associations between 1) UIC and TSH, 2) UFC and TSH, and 3) I status, UFC, and TSH were estimated using generalized linear models with gamma distribution and log link. Potential interactions between I status and UFC in association with TSH was also investigated.

Results

The cohort UIC (median: 154.2 µg/L, IQR: 92.9,271.7) indicated a population with marginally adequate I status by WHO criteria. Nearly half (n = 464, 48%) were I insufficient (UIC ≤ 150 µg/L). Median UFC (0.832 mg/L, IQR: 0.495, 1.29) was above the benchmark used to determine risk for child cognition (0.2 mg/L) (Grandjean et al., Risk Anal 2021; doi: 10.1111/risa.13767). Higher UIC was associated with increased TSH (β = 0.0003, SE = 0.0001, p = 0.01). UFC was not related to TSH (p = 0.13); however, a significant interaction between UIC and UFC was observed (p = 0.01). When analyzing only I insufficient participants, UFC and TSH were inversely associated (β = 0.1488, p = 0.0004). No association between UFC and TSH was observed for I adequate participants (p = 0.63).

Conclusions

Changes in TSH in relation to UIC and UFC were counter to our hypothesis as the relationship between UFC and TSH was inverse and only in I insufficient participants. Future research should explore if TSH is the best indicator of thyroid function in pregnancy and the mechanisms underlying the effects of pre-and postnatal F exposure on child cognition.

PFPC Comment: Unfortunately, the authors do not mention here that all women in this study were part of the ADORE cohort. [ADORE - Assessment of Docosahexaenoic Acid on Reducing Early Preterm Birth]. All women in this study were also given DHA (200 mg standard care). [DHA influences thyroid hormone metabolism]. Others received either an additional 1000 mg, or a placebo containing soybean oil - which is also well-established to affect TH metabolism.

SEE also:

Griebel-Thompson A, Sands S, Chollet-Hinton L, Christifano D, Sullivan D, Hull H, Carlson S - "Dietary and Supplemental Iodine Intake and Urinary Iodine Concentration in a Large Pregnancy Cohort in the United States" Current Developments in Nutrition 6(1):651 (2022) ABSTRACT ONLY
https://doi.org/10.1093/cdn/nzac061.035

• UPDATE: Study published in 2023:
  
  Griebel-Thompson AK, Sands S, Chollet-Hinton L, Christifano D, Sullivan DK, Hull H, Camargo JT, Carlson SE - "Iodine Intake From Diet and Supplements and Urinary Iodine Concentration in a Cohort of Pregnant Women in the United States" Am J Clin Nutr 118(1):283-289 (2023). doi: 10.1016/j.ajcnut.2023.04.005
  https://doi.org/10.1016/j.ajcnut.2023.04.005

EAR = Estimated Average Requirement
RDA = Recommended Daily Allowance

Abstract

Objectives

The EAR and RDA for iodine (I) intake in pregnancy are 160 and 220 µg/d, respectively; however, dietary I intake by United States (US) pregnant women is unknown. Several professional organizations have recommended a supplement of 150 µg/d during pregnancy, though, the current use of prenatal supplements with I is also unknown. Our objective was to determine I intake from diet and supplements and relate I intake to I status, measured by urinary I concentration (UIC).

Methods

Pregnant women (n = 966) were interviewed about their dietary intake by the Diet History Questionnaire 2.0 or multiple 24-hour recalls at baseline and their dietary I intake was estimated using the USDA, FDA and ODS-NIH Database for the Iodine Content of Common Foods (ICCF). Participants were interviewed monthly until delivery to assess I intake from prenatal supplements. Urine samples were collected between 12–20 weeks of gestation, and UIC was measured by the modified Sandell-Kolthoff reaction. A chi-square test compared groups with insufficient and adequate I status to the proportion who met the EAR for I intake.

Results

The group median intake of I from diet was below the EAR (108.8 µg/d) however, median intake increased to 188.5 µg/day when supplemental I was included. Seventy-three % of participants (707/966) had a dietary intake below the EAR and 45% (436/966) remained below the EAR after including supplemental I. The group median UIC of 154.2 µg/L indicated a population with marginally adequate I status by WHO standards. Almost half (48%) had a UIC considered to be I insufficient (≤150 µg/L) by WHO. Although slightly more than half (55%, 529/966) were taking a supplement containing I, only 27% (259/966) were taking the recommended 150 µg/d. Iodine status was significantly associated with EAR intake, with 52.1% (227/436) of those with an intake below the EAR being I insufficient (UIC ≤ 150 µg/L) compared to 44.7% (237/530) of those with an I intake above the EAR (p = 0.0229).

Conclusions

While consuming a prenatal supplement with I improved the proportion of participants with an intake above the EAR, nearly 45% of the group who consumed more than the EAR had insufficient I status.