Thyroid Function and Perimenopause: Why Checking Your Thyroid Matters
Learn how thyroid problems and perimenopause overlap, which tests to request, and how to make sense of your thyroid results.
Why Thyroid Problems Are Easy to Miss in Perimenopause
Hypothyroidism (underactive thyroid) shares many symptoms with perimenopause: fatigue, weight gain, brain fog, low mood, feeling cold, and disrupted sleep. Because these symptoms are so common during the menopause transition, thyroid dysfunction is frequently attributed to hormones and goes untested. The overlap works the other way too: thyroid problems can worsen perimenopause symptoms and make hormone treatment less effective. Testing your thyroid is one of the most important steps in getting an accurate picture of your health in your 40s and 50s.
How Oestrogen Affects Thyroid Function
Oestrogen influences thyroid hormone binding and transport in the blood. Fluctuating oestrogen during perimenopause can interfere with how thyroid hormones are carried and used by the body, even when the thyroid itself is producing normal amounts. Some women who had previously well-managed hypothyroidism find their medication needs to be adjusted as they move through perimenopause. The thyroid-oestrogen relationship is bidirectional, which is why both should be monitored during this life stage.
What Thyroid Tests to Request
The standard test is TSH (thyroid-stimulating hormone). A high TSH indicates the pituitary is working hard to stimulate an underactive thyroid. However, a TSH within the normal range does not always rule out thyroid dysfunction. Free T4 and free T3 tests provide more detail about actual circulating thyroid hormone levels. Thyroid antibody tests (TPO antibodies) can identify autoimmune thyroid disease, which is more common in women and often surfaces or worsens around perimenopause.
How to Get Tested
Your GP can order a TSH test as a basic screen, and most will add free T4. Free T3 and antibody tests sometimes require a specific request or may be done through a private clinic. The blood test is best taken first thing in the morning before eating, as TSH follows a daily rhythm and peaks in the early hours. If you suspect thyroid problems, it is worth asking for the full panel rather than just TSH, especially if you have a family history of thyroid disease.
Understanding Your Results
Standard TSH reference ranges are typically 0.4 to 4.0 mIU/L, but some clinicians suggest that a TSH above 2.5 may be suboptimal in symptomatic women. Free T4 and free T3 should sit in the mid-to-upper portion of their reference ranges for most people to feel well. If TSH is high but T4 is normal, this is subclinical hypothyroidism, which is worth monitoring and sometimes treating. Elevated TPO antibodies indicate Hashimoto's thyroiditis, the most common cause of hypothyroidism in women.
Managing Thyroid Health Alongside Perimenopause
If thyroid issues are found, treating them promptly often improves perimenopause symptoms significantly. Levothyroxine is the most common treatment for hypothyroidism. Some women do better with combination T4/T3 therapy, though this is less commonly prescribed. Nutritional factors matter too: iodine, selenium, zinc, and adequate iron all support thyroid function. If you are managing both a thyroid condition and perimenopause, working with a GP or endocrinologist who understands the interaction is valuable.
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