Association between serum iodine and thyroid function in Malagasy adults: a cross-sectional study in a tertiary-level hospital in Antananarivo, Madagascar.
This study found a significant association between high serum iodine levels and thyroid dysfunction in Malagasy adults, highlighting the need for monitoring both conditions.
Where it sits
this study against the rest of the epitalon (epithalon) corpusSummary and findings
This study assessed serum iodine levels and thyroid function in Malagasy adults at a tertiary hospital. Among 195 patients, 12.8% had serum iodine excess and 15.4% had dysthyroidism. The association between high serum iodine levels and dysthyroidism was significant.
Abstract
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 (<i>p</i>-value < 0.0001), and less common in those with hypertension (<i>p</i>-value < 0.0001), dyslipidemia (<i>p</i>-value < 0.0001), diabetes mellitus (<i>p</i>-value = 0.0082) and ex-smoking (<i>p</i>-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.
Background
This study addresses the relationship between iodine status and thyroid function in a low-income country, where such associations are not well understood. Previous research has indicated that both iodine deficiency and excess can lead to thyroid dysfunction, yet data from Madagascar is limited. Understanding these associations is crucial for public health interventions in iodine supplementation and thyroid disease management.
Methods
This cross-sectional study included 195 Malagasy adults seen at the Soavinandriana Hospital Center over two years, from September 1, 2021, to August 31, 2023. Serum iodine levels were measured, and thyroid function was assessed using thyroid stimulating hormone (TSH) and free tetra-iodothyronine (fT4). High serum iodine levels were defined as >100 µg/L, while dysthyroidism was indicated by abnormal TSH and/or fT4 levels.
Results
The primary endpoint revealed that 12.8% of patients had serum iodine excess and 15.4% had dysthyroidism. The association between high serum iodine levels and dysthyroidism was significant, with an odds ratio of 108 (95% CI: 17-680), adjusted for age and gender.
Interpretation
The findings suggest a significant association between high serum iodine levels and dysthyroidism, which aligns with existing literature on the effects of iodine on thyroid function. However, the effect size indicated by the odds ratio, while statistically significant, may not be clinically meaningful without further context. Limitations such as the cross-sectional design and reliance on serum iodine as a proxy for iodine status may confound the results, suggesting caution in interpreting the implications for clinical practice.
Key findings
- 12.8% prevalence of serum iodine excess among 195 patients.
- 15.4% prevalence of dysthyroidism among 195 patients.
- HLSI was significantly more common in subjects <60 years old (p<0.0001).
- HLSI was less common in those with hypertension (p<0.0001), dyslipidemia (p<0.0001), diabetes mellitus (p=0.0082), and ex-smoking (p<0.0001).
- Adjusted for age and gender, the association between HLSI and dysthyroidism was significant (OR=108 [17-680]).
Limitations
- cross-sectional design limits causal inferences
- small sample size of 195 patients
- reliance on serum iodine as a proxy for iodine status
- lack of urinary iodine assays