Association between Iodine Intake, Thyroid Function, and Papillary Thyroid Cancer: A Case-Control Study.

Area of Science:

• Endocrinology
• Oncology
• Nutritional Science

Background:

• Thyroid cancer, including papillary thyroid cancer (PTC) and papillary thyroid microcarcinoma (PTMC), is a growing health concern.
• Iodine intake and thyroid function are critical factors influencing thyroid health.
• Understanding their combined impact on PTC and PTMC risk is essential for prevention and management.

Purpose of the Study:

• To evaluate the individual and combined effects of iodine intake and thyroid function on the risk of developing papillary thyroid cancer (PTC) and papillary thyroid microcarcinoma (PTMC).

Main Methods:

• A case-control study involving 446 PTC/PTMC cases and 500 controls.
• Urinary iodine concentration (UIC) measured to assess iodine intake.
• Serum free thyroxine (T4) levels assessed for thyroid function.
• Unconditional logistic regression used to estimate risk.

Main Results:

• Excessive iodine intake (UIC ≥220 μg/gCr) was strongly associated with increased risk of both PTC (OR, 18.13) and PTMC (OR, 8.02).
• High free T4 levels (≥1.25 ng/dL) were also linked to higher risks of PTC (OR, 1.97) and PTMC (OR, 2.98).
• The combination of excessive iodine intake and high free T4 levels demonstrated a synergistic effect, significantly elevating the risk for both PTC (OR, 43.48) and PTMC (OR, 26.96).

Conclusions:

• Excessive iodine intake and elevated free T4 levels appear to have a synergistic impact on the risk of papillary thyroid cancer and microcarcinoma.
• Assessing both iodine intake and thyroid function is crucial for a comprehensive risk evaluation of PTC and PTMC.