The Claim
Selenium deficiency is associated with an elevated free T4 to free T3 ratio, and this elevation is reversed upon selenium repletion.
What the research says
Supports is higher
Support is ahead, but a single strong opposing study can change this.
These are independent scores, not a percentage. Higher-grade studies count more, so a single strong opposing study can outweigh several weaker ones.
Low selenium levels are linked to a higher ratio of free T4 to free T3 in the blood, and restoring selenium levels returns this ratio to normal.
See the scientific wording
Selenium deficiency is associated with an elevated free T4 to free T3 ratio, which is reversible with selenium repletion.
When selenium is low, the enzymes that turn the inactive thyroid hormone T4 into the active hormone T3 don't work properly. This causes T4 to build up and T3 to drop, raising the ratio of T4 to T3. When selenium is restored, these enzymes start working again, T4 gets converted to T3, and the ratio returns to normal.
What the research says
4 studiesWhen the body can't use selenium properly, it struggles to convert the main thyroid hormone (T4) into the active form (T3), making T4 build up relative to T3. This matches the claim that low selenium leads to a higher T4-to-T3 ratio.
Study: Thyroid function in patients with selenium deficiency exhibits high free T4 to T3 ratio
When people don’t have enough selenium, their bodies struggle to convert one thyroid hormone (T4) into the more active form (T3), making T4 build up relative to T3. Giving them selenium supplements fixes this imbalance and lowers T4 while raising T3.
When people don't get enough selenium, their bodies make too much inactive thyroid hormone (T4) and not enough active one (T3). Giving them selenium supplements fixes this imbalance — more T3, less T4 — and helps them feel better and live longer.
Study: Selenium Status Associates with Thyroid Hormone and Thyroid Dysfunction in Older Chinese Adults
When people have more selenium in their blood, their bodies tend to make more of both thyroid hormones T3 and T4. Since selenium helps turn T4 into T3, it’s likely that low selenium causes T4 to build up compared to T3 — which matches the claim. Restoring selenium probably fixes that imbalance.
Related videos
Score breakdown, mechanism chain, raw evidence, ideal studies needed & 4 supporting studies
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.