Effect of Thyroid Status Modulation on Pituitary and Peripheral Hormone Concentrations in Healthy Older Subjects

Thyroid hormone doesn’t directly make sex hormones like testosterone or estrogen, but it helps the body’s sex glands work properly so they can produce these hormones at the right levels.

Taking one pill of a thyroid hormone called T3 might cause older men to temporarily produce more testosterone and a related hormone, which could help explain why thyroid and sex hormones might be connected as men age.

In older adults who are healthy, giving them thyroid hormones (either through a shot or a pill) can make a key growth-related protein called IGF-1 go up by 6–9% in just one day — and this might happen even if their growth hormone levels don’t change.

When older adults get more thyroid hormone—either through a shot or a pill—their prolactin levels drop by about 8–12% in just a couple of days, and this drop is bigger in men, suggesting thyroid hormone naturally lowers prolactin no matter how you give it or whether you're male or female.

When older adults without thyroid problems are given hormones that boost thyroid activity, their stress hormone (cortisol) drops by about 12–16% over a couple of days, which suggests that the thyroid and stress systems talk to each other.

When healthy older men take a single pill of a thyroid hormone called T3, their body makes more of a hormone that tells the testes to work harder — but another hormone called TSH doesn’t do this, which suggests T3 has a special role in controlling this process.