thyroxine and blood sugar

It's confirmed.




24 Replies

  • Ella - yes, it does raise blood sugar. However, if you don't have diabetes, your body's normal production of insulin counteracts it. Diabetes and hypothyroidism are often found to co-exist. To be clear, thyroxine doesn't give you diabetes - there was sonething already wrong if taking it causes your blood sugar to rise.

  • jazz - I would like to know why does thyroxine raise blood sugar?

    I don't know what was wrong with my body but it's not only me who noticed a change towards prediabetes with thyroxine.

    If it raises the blood sugar, it means it raises the insulin and increases the fat around and within the body. That's why I am overweight.

    As I am taking responsibility for my own health, I'll see what will happen along the way when implementing Dr P's protocol.

    From the biochemistry point of view, I am just curious what is the relationship between the insulin and thyroxine

  • Well, thyroid hormones regulate metabolism. The more thyroid hormones you have, the higher your metabolism works. And basically, your metabolism is based on your ability to break down nutrients. So if you put thyroid hormones into a body which previously didn't have as much as it should have had, your body will start breaking down glucose, and then fat, much more quickly, meaning your blood sugar would rise. In a person who is otherwise healthy, the body would produce just enough insulin to regulate blood sugar, so no problem. However, if you're at all insulin resistant, either because you have pre-diabetes or full blown type 2, insulin levels will remain higher than they should, promoting storage of fat.

    This is of course not exactly how it works - I've missed a few steps - but hopefully enough to get the picture. I think if your blood sugar stays high when you take thyroxine, it's probably a sign that you have insulin resistance in addition to thyroid problems. Taking Liothyronine or NDT would similarly raise blood sugars if your body's insulin response is impaired.

  • Thyroid levels that are too high OR too low will result in insulin resistance. I would be inclined to think that if you are on a low dose of T4, that your condition would improve with the addition of some T3. Likewise, if someone is on high doses of T3 and blood sugar is rising, their condition might improve if they lowered their T3. It's all very complicated, because the endocrine system is so intertwined. There's some info here:

  • Thanks for this link 😊

  • You're welcome. I think the problem is that few patients take a truly physiological dose. Many lack T3, others lack T4, or the ratio's just off.

  • But it's so difficult to get right, isn't it! My blood sugar is always pretty good so I guess I'm ok. Unfortunately I have to take t3 only as I can't tolerate t4 at all (I keep trying). As my TSH has always been low since being on thyroid mediation, I'm going to ask to be checked for insulin resistance. Perhaps this is the missing link I've been looking for! just because my blood sugar is ok doesn't mean I don't have an element of insulin resistance. It is certainly worth checking.

  • Yes, trial and damned error lol! You might check A1C.

  • A1c is raised, falsely, with hypothyroidism..really not a good test for hypo's. A person does not have to have a ratio or need t4. There are many here not converting and on t3 only. Non conversion is very common with type 2.

  • Low free t3 can also cause insulin resistance.

  • there was someone else on either this forum or the Facebook one recently reported that his doctor told him (I think it was a chap) that as he had thyroidism then he would 'of course' become diabetic. At the time there was a chorus from everyone poo-pooing the doctor's lack of knowledge. Maybe not so much, eh?

    For what it's worth, in the past 3 years, after the original weight gain on T4 only treatment, I have tried NDT and T3 only treatment - and not a single pound of weight have I been able to shift. Indeed, it takes me all my time to prevent any more going on.

  • It was previously believed that levothyroxine increased blood sugar if you already had diabetes or pre-diabetes, both of which are common complications of having an under active thyroid. There is now a theory that it may cause a rise in blood sugar in some non-diabetic patients. This, however, is based on a study of non-diabetic horses. I haven't yet found a study involving non-diabetic humans (still looking).

    There is also the possibility in non-diabetic humans that their blood sugar level before getting their thyroid treated was lower than it would have been without hypothyroidism and that the addition of thyroxine actually normalised levels. I guess more research needs to be done to find out if this is actually the case.

    I think at this stage there is not enough comprehensive data on this in non-diabetic patients to know if this is a risk but It is believed that not treating hypothyroidism means you are more likely to develop diabetes. If you have diabetes or pre-diabetes/insulin resistance you absolutely must monitor your blood sugar carefully on starting levothyroxine or changing dosage. Unfortunately, as yet, no one really knows the full implication on the health of non-diabetics. Bear in mind this isn't limited to levothyroxine. Blood sugar also rises on taking NDT.

  • What is NDT?


  • Thank you :)

  • I stopped taking thyroxine for the last 2 weeks. My fasting sugar is now below 6. Today was 5 yesterday 5.3. This is the only variable that I changed.

    Before that I have reduced T4 from 75 to 50mcg but my fasting sugar was still high (over 6). Dr C said that I have metabolic syndrome, insulin resistance and probably diabetes. I am determined to prove him wrong.

  • 007999 - metabolic syndrome? How can that be proved, or not?

    Are you taking any thyroid meds?

  • Metabolic Syndrome is defined as a cluster of biochemical and physiological abnormalities associated with the development of cardiovascular disease and a type 2 diabetes.

    In my case it manifested itself by high blood pressure, raised fasting blood sugar, high cholesterol, weight gain.

    At this moment I do not take any thyroid meds as I want my adrenals to pick up first. However, as I also have Hashi so I pay attention to an autoimmune diet and stress (chemical, physiological and emotional).

  • Thanks 007999 for explaining.

  • I have this cluster too. If you are not converting the t4 to t3, you stay hypo, because of low t3 levels and develop type 2. But, with Hashi's especially, the inflammation can cause it. Hypo causes false high in A1c. I am sorry that i am tootired to find the links right now!

  • I have a theory that if levo is T4 alone (which is a storage hormone) then by associationit must help you gain weight.

  • Since Thyroid raises metabolism, it would raise blood sugar. Your body should make enough insulin to handle this increase. There are many Hypothyroid people with very low blood sugar. Type 2 can be caused buy low free t3 tho. because it is a disease that is caused by inflammation, in part. Hypo's and especially Hashi's, have lots of inflammation. If a person is hypo, they need thyroid meds, but the right ones.

  • I am Hypo, and was told when I started that Diabetes was linked and I need to be careful. My last bloods showed increase sugar level and have been told I am pre-diabetic, but if thyroxine increases the blood sugar then surely that would make me pre-diabetic?? I am confused as she didn't say anything about insulin resistance.

  • Some years ago, while working in Cambodia, I attended a big international hospital in Bangkok for various tests. (Cambodia didn't have any decent hospitals). When the results came in the specialist who saw me told me in a very shirty way that I was pre-diabetic. This came as a big surprise as I hadn't been into sugar at all. So perhaps thyroxine does raise blood sugar in some way.

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