Thiocyanate overload, poor dietary diversity, and selenium/iron co-deficiencies sustain iodine deficiency disorders in sub-Saharan Africa

Background Persistence of iodine deficiency disorders (IDD) and endemic goiter in sub-Saharan Africa (SSA) is multifactorial, involving not only inadequate iodine intake but also other co-dietary factors. Objective This systematic review synthesized evidence from primary human research on the roles of thiocyanate (SCN) overload/dietary goitrogens, poor dietary diversity, and selenium/iron co-deficiencies in sustaining IDD and endemic goiter in SSA populations. Methods Reported in accordance with PRISMA 2020 guidelines, the review searched PubMed, Embase, Web of Science, and African Index Medicus for studies published primarily from 1990 onward. Eligible studies were original observational or interventional human research conducted in SSA that quantitatively assessed at least one specified co-dietary factor in relation to goiter prevalence, urinary iodine concentration (UIC), or thyroid function. Results The SCN overload was associated with elevated goiter risk (Adjusted Odds Ratio [AOR] up to 3.74), reduced UIC, and biochemical interference with iodide uptake and thyroid peroxidase activity. Poor dietary diversity independently increased goiter odds (AOR up to 3.32) through reliance on monotonous staples. Selenium co-deficiency impaired deiodinase activity and antioxidant protection, while iron co-deficiency significantly reduced the efficacy of iodine repletion, halving thyroid volume reduction and doubling goiter persistence in children with anemia. These factors frequently interacted, sustaining high goiter prevalence (16-100%) despite varying USI coverage and median UIC values often approaching sufficiency (65.5-152 μg/L). Conclusion These findings highlight the need for integrated interventions beyond USI alone, including improved food processing to reduce goitrogenic potential, promotion of dietary diversity, and targeted multi-micronutrient supplementation to achieve sustainable IDD control.