Association between serum iodine and thyroid function in Malagasy adults: a cross-sectional study in a tertiary-level hospital in Antananarivo, Madagascar

Iodine status and thyroid disorders remain understudied subjects in low-income countries such as ours. The objectives of the present study were to assess the serum iodine (SI) level and thyroid function in Malagasy adults seen at the Soavinandriana Hospital Center in Antananarivo and to determine the association between high levels of serum iodine (HLSI) and dysthyroidism. This cross-sectional study was conducted over the course of two years (September 1, 2021 to August 31, 2023). The SI was used as a proxy for iodine status in the absence of urinary assays. Thyroid function was assessed by thyroid stimulating hormone (TSH) and free tetra-iodothyronine (fT4). The HLSI was defined by the total serum iodine >100 µg/L. Dysthyroidism was defined by abnormal TSH and/or fT4 levels indicative of hypo- or hyperthyroidism. Among 195 patients, the prevalences of serum iodine excess and dysthyroidism were 12.8% and 15.4%, respectively. HLSI was significantly more common in subjects <60 years old (p-value < 0.0001), and less common in those with hypertension (p-value < 0.0001), dyslipidemia (p-value < 0.0001), diabetes mellitus (p-value = 0.0082) and ex-smoking (p-value < 0.0001). Adjusted for age and gender, the association between HLSI and dysthyroidism was significant (OR = 108 [17–680]). HLSI and dysthyroidism were prevalent among Malagasy adults. The presence of one condition would encourage the search for the other. Their management is primarily preventive through their periodic monitoring.