The link between thyroid health and women's hormones
How thyroid function affects women's hormones and the menstrual cycle, the signs of an underactive and an overactive thyroid, and when to see a doctor.
Thyroid hormones affect almost every system in the body, and they have a direct effect on the production of women's reproductive hormones and on the menstrual cycle. When thyroid function is not what it should be, irregular periods, problems with ovulation and a range of other symptoms can follow.
Why does thyroid hormone matter?
The active thyroid hormone, T3, plays a key part in converting cholesterol in the cells into pregnenolone — the raw material for the sex hormones progesterone, oestrogen and DHEA. When thyroid function is inadequate, this conversion can falter at cellular level and affect the production of oestrogen and progesterone.
Thyroid function and the menstrual cycle
Oestrogen stimulates the thyroid gland by increasing the secretion of TSH. High cortisol from stress, by contrast, can suppress both the release of TSH and the conversion of T4 into active T3, and so lower thyroid hormone levels. The raised prolactin that often accompanies an underactive thyroid can suppress oestrogen production in the ovaries and progesterone as well, so that ovulation becomes irregular. Thyroid disorders are among the commonest hormonal causes of irregular periods and ovulation problems in women.
Signs of an underactive thyroid (hypothyroidism)
- marked tiredness and lack of energy
- weight gain
- feeling cold, poor tolerance of cold
- dry hair and skin, hair loss
- irregular periods, heavy bleeding
- swelling (oedema), muscle and joint pain
- constipation
- low mood
Signs of an overactive thyroid (hyperthyroidism)
- a faster heart rate, palpitations
- poor tolerance of heat, excessive sweating
- weight loss despite an increased appetite
- irritability, mood swings
- trembling hands
- irregular periods
- faster bowel movements
When should you see a doctor?
If irregular or absent periods come together with a goitre, palpitations, prominence of the eyes or milk from the nipple, having thyroid and prolactin levels assessed is advisable. A doctor — an endocrinologist where necessary — should be seen by women who are planning a pregnancy or are pregnant, where a medication dose cannot be settled, where a nodule (a firm lump) is found in the thyroid, or where thyroid test results are inconsistent.
Frequently asked questions
When should thyroid tests be done? Where there are no symptoms, measuring TSH is sufficient for screening. Where an underactive thyroid is suspected, TSH and free T4 are assessed; where an overactive thyroid is suspected, TSH is assessed together with free T4 and free T3.
Is a thyroid problem the only cause of irregular periods? No. Irregular periods can have many causes; the thyroid is only one of the important ones that needs to be assessed.
What if I take high-dose biotin? High-dose biotin can distort thyroid test results. Tell your doctor that you take it, and it is generally advised that it be stopped at least 48 hours before the test.
This page is for information. It does not replace an examination or individual medical advice.