Hypothyroid & Levothyroxine impact

Going through breast cancer treatment Hormone therapy
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Anyone else dealing with thyroid issues and taking levothyroxine?

I read levothyroxine can potentially cause breast cancer. Your thoughts on this?

T4 was high in my last test, so not sure if the hormones might fuel ep+pp+ to reoccur? Wondering if I need to stop taking levothyroxine, but not sure I can. I have an appointment with an endocrinologist.

What about post-menopause impact on thyroid and estrogen?

Besides checking the TSH, few other things to get checked:

Free T3

Free T4

TPOab (thyroid peroxidase antibody)

TGab (thyroglobulin antibody)

TSH may be normal, but high T4 could mean hyperthyroidism.

Also note that not all thyroid medicine is the same. There are fillers added to different types of Levothyroxine and where it is produced can also make a difference. Tirosint offers a liquid version, but it is expensive. Levoxyl brand name is a less expensive option, supposedly with less fillers.

One question that continues for me is the role of estrogen in both breast cancer, but also helping to protect the heart, etc. If you suppress estrogen, are you causing more harm to the heart and other benefits of estrogen? Some women take hormones during menopause, but then other women take hormone blockers because of breast cancer.

Also note the connection between cholesterol and hypothyroidism. Everything is tied together, so there is a delicate balance once you start taking medication to prevent one thing, it can harm something else. It is critical to work with an doctor/oncologist who looks at the whole picture, not just treating breast cancer.

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Yes me. Having taken levothyroxine for about 8 years in 2024 blood results were abnormal. At the sametime I was diagnosed with breast cancer. Surgery, + second op to get clear margins plus 15 radiotherapy sessions. Managed all ok but thyroid still unstable. Taking Letrozole from diagnosis October 2024. Mid 2025 dexa scan found I have osteoporosis in spine and osteopenia in hips. Thyroid still unstable, now taking both sides hyroxine and carbimazole ( called block and replace). Aches and pains everywhere but not sure who to ask for help.

Do I think it was caused by levothyroxine? I don’t know maybe just coincidence but wish it would all get sorted soon. Hope you find answers

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Hi there. I have had hypothyroidism and been on levothyroxine for about 25 years, since I was 40ish. I have not heard of a link between thyroid disease and breast cancer and none of the doctors I have seen in the 2 years, since I was diagnosed with breast cancer, have mentioned one. I would not be able to stop my levothyroxine as I know I would become symptomatic quite quickly and I can’t function properly then, let alone all the BC treatments etc. The brain fog from letrazole is real and if I was hypothyroid too it would be worse!

I became post menopausal at about 46 years and the menopause didnt seem to affect my thyroid or thyroxine dose. I have had no dose changes while going through BC treatment- chemo,surgery, radiotherapy, Letrazole, Abemaciclib and Zoledronic acid. In fact I’ve only had 1 dose change in 25 years, about 6 years or so ago when I had some palpitations and the dose was found to be too high.

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Hi, I developed thyroiditis whilst taking the 2 year course of adjuvant Abemaciclib. At first I was hyperthyroidism and then developed hypothyroidism . Although 95% of people who develop thyroiditis recover completely unfortunately I have been left with hypothyroidism and I am on 50mcg of levothyroxine daily.

When I was first diagnosed with thyroid problems I did do some research into thyroid disease and breast cancer. From what I remember hyperthyroidism was linked to an increased risk of breast cancer and hypothyroidism was linked to a decreased risk of breast cancer. My TSH has been around 2. Endocrinologist did suggest I increase my levothyroxine but I decided to stay on 50mcg because of the studies I had read.

I have not read the study that you mention in your post so I can’t comment on it, but often several studies that all come to the same conclusion are required before medical practice is changed.

If our thyroid isn’t functioning properly I don’t think we have much choice but to take levothyroxine.

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