Dairy Intake and Iodine Status in Pregnant and Lactating Women: A Systematic Review and Meta-Analysis

Abstract

Background/Objectives: Despite salt iodization, iodine deficiency during pregnancy and lactation is re-emerging in many industrialized countries, necessitating an evaluation of the role of dairy in supporting iodine status during these critical periods. Methods: We conducted a systematic review and meta-analysis in accordance with PRISMA guidelines. Ten databases were searched through March 2025 using ProQuest Dialog™ (Version 75.0). Study quality was assessed using either the Quality Evaluation for Observational Studies tool or the Risk of Bias 2 tool, depending on study design. Random-effects models were applied, with certainty of evidence rated using the GRADE framework. Publication bias, sensitivity analyses, and subgroup analyses were also performed. Results: Fifty-one publications met the eligibility criteria, including 50 publications of observational studies and 1 publication of a randomized controlled trial (RCT), with most studies conducted on pregnant women. Higher dairy intake was associated with significantly greater urinary iodine concentration (UIC), (23 studies; standardized mean difference: 0.326; 95% confidence interval [CI]: 0.228, 0.424; p < 0.001; I2 = 57.31%; low-certainty), and significantly lower odds of iodine deficiency (11 studies; odds ratio: 0.58; 95% CI: 0.48, 0.70; p < 0.001; I2 = 0%; moderate-certainty). Associations were stronger in studies conducted during later pregnancy, in higher-quality studies, and when the dairy food was specifically milk. Dairy contributed to ~27% of iodine intake from foods. Breast milk iodine concentration (BMIC) findings were inconsistent, though in one RCT, iodine-fortified milk improved BMIC and UIC. Conclusions: Dairy intake supports adequate iodine status during pregnancy and lactation. RCTs would be valuable in further investigating the role of dairy in supporting iodine status, particularly in lactating women. (PROSPERO CRD420251054576)