In older adults with low selenium levels, taking selenium and coenzyme Q10 supplements is associated with higher levels of reverse T3, a thyroid hormone metabolite, which may indicate a biological adjustment to lower metabolic activity.

In older adults with low selenium levels, taking 200 micrograms of selenium and 200 milligrams of coenzyme Q10 daily for four years is associated with an increase in free triiodothyronine and a decrease in free thyroxine, indicating a change in thyroid hormone conversion that may influence metabolic and cardiovascular health.

In older adults with low selenium levels, taking selenium and coenzyme Q10 supplements for four years results in a smaller rise in thyroid-stimulating hormone (TSH) levels compared to taking a placebo, and fewer people reach the TSH level that defines subclinical hypothyroidism.

In older adults with low selenium levels, low levels of the thyroid hormone fT3 are linked to poorer mental and physical well-being. Taking selenium and coenzyme Q10 supplements removes this link and improves energy levels, reduces bodily pain, and enhances social functioning.

In people with low selenium levels, taking selenium supplements lowers free T4 and the ratio of free T4 to free T3 while raising free T3 levels, suggesting that selenium plays a role in how the body converts thyroid hormones and that this process can improve with supplementation.

People with low selenium levels have lower amounts of free T3 hormone in their blood compared to those with normal thyroid function, but their free T4 and TSH levels do not consistently rise, suggesting the issue is not with the thyroid gland itself but with how the body converts thyroid hormones in peripheral tissues.