Recent research reveals T4 has a specific effect in promoting cancer growth, the more T4 the more cancer. T3 has a much smaller effect on an equivalent dose basis (L-T3 is 3x as potent as L-T4).
An exception is breast cancer which seems to respond to the oestrogenic effects of thyroid hormone (T3 binding to nuclear receptors), so the more hormone the higher risk, whether you are taking L-T3, L-T4 or NDT.
I hope to publish a detailed summary early next year but it seemed morally wrong not to raise awareness as soon as possible. I have briefly mentioned it in posts but found I end up hijacking the posts as people are naturally interested. I won't mention it any more, apologies to those who have had their posts distracted.
I don't want to get into detailed discussion at this point but please be aware that the higher fT4 is the greater the risk from cancer. These effects take a very long time so waiting a few months for more information shouldn't be too much of a problem. Basically, if you can reduce your T4 levels a little and still feel well do so.
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jimh111
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There seems to be an urgent need to properly identify what is happening.
First, does thyroid hormone (T4 or T3) have any role at all in the origin of cancers?
Second, is there a point at which T4 changes from having little effect to having a significant effect?
Imagine you are taking 125 T4. But that is barely enough for you. So you increase to 150 which makes FT4 rise to somewhere around top of the reference interval. Does the 25 increment have the same cancer promotion properties as the original 125? Or one fifth? Or twice as much? That is, is the impact linear with respect to dose? Or not?
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The effect appears to be linear. e.g. lower quartile has less effect than 2nd, 3rd or 4th. There's even some studies that show little difference between 2nd and 4th quartile. So the evidence is confusing, it always is in these things. I plan to raise the issue and leave the fine analysis to oncologists, they have dealt with such complex data for decades.
Although T4 seems to have a small effect in 'initiating' cancers it has a far greater effect in making cancer more agressive. This is important as the general approach to drug safety is to look at cancer 'cases' and not progression. As Hidden mentions there is so much evidence it's quite a task to try and separate out the relevant stuff and present it in an informative way that seeks out the actual risks to patients.
The point is levothyroxine monotherapy carries much higher risks than combination therapy and so should not be used routinely.
The topic you’re exploring is very important. That said, it’s more important that sentences like your last one are not presented as proven without evidence from a named source. Of course, there is also dissension as to the facts even when they are from named sources.
This can be a risk to patients who decide to stop taking medication on the basis of what they have read.
Cancer cells differ from other cells in that they grow really rapidly and given how I felt when I was on Levothyroxine like how they describe people using amphetamines I would really like to know Jim's sources and if their is any validity. Sadly here in the U.S.A. there seems to be a level of recklessness in "healthcare" and so open discussion is so very beneficial. Knowing what questions to ask doctors and not accepting blindly what they say may in fact save lives. I wish I had known half of what I have learned on this site back in December 2012. Thank you for everyone's generous sharing.
“The point is levothyroxine monotherapy carries much higher risks than combination therapy and so should not be used routinely.”
Please be mindful that combination therapy is not offered on the NHS in the vast majority of cases. This is a hard statement for those of us who are unable to access it to read.
That was one reason I asked the question about how the dose relates to the impact on cancer.
For discussion, if the increment from 125 to 150 had ten times the impact of the original 125 (as per my example earlier), then it could make a huge difference to choose to take a combination of 125 levothyroxine plus a little T3 (I'd guess 5 to 10 micrograms). Broadly, make it equivalent to the 150 dose, assuming that was working well. That would reduce the impact on cancer dramatically.
But, if the impact is much more even, then the argument is less easy to argue and implement.
I see. As far as I've seen there is no cliff edge, it's linear(ish). The really difficult task is to quantify the risk, which is what I'm working on next. This will not be precise, the data isn't that good but even a wide range of mortality risk is good enough to make a decision to adopt treatment to reduce risk.
Very roughly speaking it looks like 50 mcg L-T3 will have less effect than 150 mcg L-T4 (except for breast cancer). My view is that for most people with primary hypothyroidism we should aim for a more physiological approach with a little T3 and less T4. This mightl put thyroid patients in the same boat as the general population. There is a problem for those of us who need higher hormone levels, if we are aware of it we can be vigilant and push for more urgent and fundamental research into the various forms of hypothyroidism.
Thank you for that! Immaterial of side effects, it is for me, however, 'what it is', including some improved heart symptoms. I've had a long, unnecessarily shady, path through this quagmire from summer 2003. Without Dr S and Dr P in 2010... who knows where I'd be now?
Summer 2015 got up to taking 75 mcg of Liothyronine in winter, dropping to 62.5 in summer, also 5 yrs in with NHS prescribed Armour T I was 'dissuaded' by an NHS endo, (I'd gone to see for x reason, yet which was ignored), then Armour stopped via his 'expert' sanction. With a temp of 35.7C, even in his presence - it had been 34.5C in the height of summer (using BOTH hormones) - I left 'undx'd', yet where GP and NHS guidelines had been accepted/adhered to throughout.
Sadly, despite much research, 'they' simply ignore any/everything that doesn't suit some of their utterly bizarre notions. Seemingly, way more than research is needed to break through their Boys Club' stranglehold.
What is the effect of someone being prescribed Levothyroxine when in fact an incorrect dx has been made . Is it more than causing the pituitary gland to atrophy can cancer indeed be triggered? This is a serious question and not some pot stirring nonsense. My former doctor I now realize was in overdrive about cancer and keeping everyone's BP at 90/50. I am guessing here in the U.S.A. he is not alone acknowledging there are many fine "healers" struggling to practice in a very broken system.
But, if levothyroxine has an impact regarding cancer, I suggest it is likely only to affect some people - maybe a genetic subgroup but there are other possibilities.
Taking a population statistic (e.g. cancer in those taking levothyroxine), and trying to apply them to specific individuals who take levothyroxine, is not based in logic, science or maths!
In the UK we are consistently told by GPs and Endos that the only thyroid related hormone level that matters is TSH. Hence T4 levels are rarely, and certainly not routinely, tested in the vast majority of patients in the UK.
From studies that look at data that includes fT4 assays carried out some time before a cancer presentation (cancer can alter thyroid hormone levels). I will give references when I write it up).
Just wanted to say , i agree with you Jim . It's right we are aware that this could be a potential concern., even if we are a long way off knowing the full picture yet.
I first became aware of little snippets of information suggesting T4 (the natural sort we make ourselves) has role in cancer proliferation ,when reading research papers looking into whether rT3 blocks t3 receptors..
Due to my history of my levo dose giving me fT4 often over range (120% ish) in the past, and recently very high over range (up to 240% ) i had been looking to find any validity in not only the alleged risk factors for under range TSH , but also any information about over range fT4 linked to any problems.
As a result of the little snippets i saw, (which from vague memory was something to do with rT3 and ?T4 receptors also having a role in cancer cell proliferation) i got the impression that everybody's T4 level, whether the T4 is from the body or from Levo , will be having an effect on how much cancer cell proliferation is promoted.
I'm not too worried, because obviously if T4 does have this effect , it will also be happening to the whole population, (along with everything else in our lives/environment that may also promote cancer) ... but maybe more so, to those with higher T4 levels , and less so, to those with lower fT4 levels .... higher than 'what' / lower than 'what ' ?....... obviously nobody knows yet, and i suspect like everything else 'thyroid ' it's probably very individual anyway.
But i too, think it would be irresponsible to carry on saying "there is absolutely no problem with having fT4 over range" once we have become aware that there just might be one.
I also think that if this does turn out to be a significant issue.. it might actually be useful to the campaign for more physiological thyroid hormone replacement .... if research shows there are risks related to T4 level, and since it is known that those taking Levo alone have relatively higher fT4 / lower fT3 levels than they will have had previously .... then we have another argument for why aiming for a more physiologically natural balance of T3 and T4 levels should be the first aim of treatment , rather than just using Levo alone.
Of course we would still have to face the fact that the first response to this by many endo's would just be to advise lower T4 levels on Levo ,and not give a stuff if you felt less well like that .
.... but there are endocrinologists who currently take the view "some of my patients need slightly over range fT4 on Levo to feel well, and i don't mind them doing this.... "
and some of them might wonder if a small addition of T3 could be preferable to using higher T4 to achieve well being..... and they may have grounds to say so publicly if there is proof that higher T4 also carries some risk.
I think that getting endocrinologists to consider using a little T3 to produce closer to physiologically 'natural' T4/3 levels is surely a small step in the right direction towards T3 use becoming more generally accepted... which would eventually help those who need more than 'a little'.
Call me 'over optimistic' if you like ... but i live in hope .
I don't have references at the moment either, (other than a couple to thyroid patients.canada articles on cancer ... which i do trust to be properly researched and referenced).
I did save the other references at the time i found them ,but i can't currently remember which of my 100's of 'saved' papers they are in.
So yes , i could be said to be causing worry without backing it up with evidence.. for which i apologise. I'm personally not particularly worried about it at the moment .. i just put the question "does T4 level relate to cancer proliferation level , what dose this mean ,and does this matter ? " into my "bear this in mind, and learn more about it " box.
To anyone reading this and thinking "but what exactly are you saying is risky, and what should we do about it ?" ..........I'm not suggesting anyone DO anything about it at the moment, apart from ." if it concerns you, do as much reading of research as you can and see what you find",.... but don't get it out of proportion ... we all encounter 'increased cancer risk' from lots and lots of things that we all come across every day.
Thanks so much for this reply, it expresses my thoughts in a way I was unable to do. It is T4 that carries the risk, for everyone, and there have been trials of reducing T4 (or blocking its action on the integrin receptor) that are in the experimental stage and are proving to be an effective treatment for existing cancer. I leave this to the oncologists, but it's supporting evidence.
For the meantime I would just say try to avoid higher T4 levels if you can (and most people can't), just be aware it's a long term issue and be vigilant.
I suffer from secondary hypothyroidism and take levothyroxine of 100 mcg (to achieve TSH of 1,5) or 125 mcg (to achieve TSH under 1) daily. I have suffered from prostate cancer (hopefully in remission as per last MRI), I would be most grateful to hear of linkage between T4 and prostate cancer and recommended actions to promote better health and survival.
To add to my last post, I was diagnosed with hypothyroidism and Hashimoto’s disease in 2014. I was prescribed levothyroxine dosages starting at 50 mcg rising to 150 mcg then reducing to 100 mcg. My prostate cancer was diagnosed in 2018. I wonder if my levothyroxine medication or hypothyroidism led to my prostate cancer.
I’m sorry I haven’t seen any specific studies on prostate cancer and thyroid hormones, I believe prostate cancer is the most common cancer in men. To be clear I do not have any knowledge of cancer beyond the average person in the street.
I was interested in studies that suggested T3 might reduce COVID infection and came across the integrin receptor which binds T4 and has a role in cancer proliferation. I then looked at studies linking T4 to cancer. So, I’m only looking at numbers, I don’t have any cancer knowledge and so can’t give advice. Sorry.
I will try hard to get it written up early next year. In the meantime it will help if I don't get too many requests for evidence. We need evidence but I'm trying to signal an early warning with the promise I will back it up with an attempt at a balanced presentation.
I have so much I want to say on this subject, in particular with regard to terminology such as study, research and evidence.
However, I shall desist for the moment and look forward to you upcoming presentation.
In the meantime, perhaps you and others would be interested in this year old TUK thread which proves, if nothing else, that opinions play a large part in study, research and evidence.
I was on 200 mcg of Levo and well over range for approx 18 years . Also on HRT 4 years ago I had breast cancer : no clinician ever discussed the risk of either meds.
My cancer histology was oestrogen receptive so I stopped HRT. After about 6 months I simply could not stand it any longer - and after discussions with oncologist and my own research on published risks, I restarted HRT, with no regrets.
I have for some time been concerned about my T4 but any attempt to reduce it made me unable to function. Only this year I have been able to reduce it and add T3.
I feel probably as well as I ever have in the last 15 years.
I will never know now if either T4 or HRT contributed to my developing BC. At the moment I am NED -‘ and tbh I hardly every think about it .
This is a massively complex issue and I am overwhelmingly influenced by how well I feel - rather than potential risks .
Many people are in the same boat. I would always advise to take the advice of an oncologist rather than myself (or endocrinologist!) on the issue of cancer. They are the experts at the analysing complex data that comes from cancer studies. I hope you remain clear in the future.
In the longer term my interest is finding why some of us need higher thyroid hormone doses and see if we can find answers ways of discontinuing thyroid tablets or recover on doses that deliver normal hormone levels. Once there is acceptance that some patients need high doses of hormones there should follow curiosity as to why.
Thyroxine (T4) whether it is from the thyroid or levothyroxine tablets or dessicated thyroid (NDT). It's T4 that has the effect no matter where it originates from, from your thyroid or from tablets.
Oh yes, I agree with all of that! The problem I experience time and again is the lack of an holistic view of medication/treatments and how they interact , or what effect they have on QOL by any clinician I have seen.It was the same when I cared for my mother years ago and I’ve had the same issues with my daughter’s (far too) many medications .
In the end we are left to make our own minds up.
The work people like you do - and the people in this group is invaluable .
Incidentally - wrt to breast cancer treatment, I found a tool called NHS Predict which let you put in all the details of your diagnosis and histology and it delivers a value of treatment over 5 and 10 years. Easily available on ‘net but not mentioned by anyone I saw . The drug I tried and stopped showed an advantage of half an extra person surviving over 10 years based on my details
I showed it to my oncologist. He was a lovely guy, respected my decisions but still wanted me to try it again .
It was a very lonely place to be and I think many of us feel that way about our various treatments.
But it is great to find information from fellow sufferers and to read the experience of others.
I’ve never consider being able to stop thyroid meds ! But what a great thought 🙂
Thank you for starting this very interesting discussion as I always thought that my breast cancer had somehow followed on from having an overactive thyroid which resulted in a thyroidectomy. Interestingly I was on no thyroid medication when it happened.
Studies suggest there is a link between breast cancer and thyroid hormone (both T3 and T4) but as in many of these sort of studies it doesn't seem 100% conclusive. Going from memory of what I've read so far it appears to be in post menopausal women so younger women don't need to worry about it.
I actually was around 45 at the time but suddenly remembered that I had been on carbimazole for a year before the thyroidectomy and of course was overactive even before that. It's all very interesting especially as I've just gone overactive again at the age of 70 and wonder if cancer will strike again (fingers crossed).
Fingers crossed. It demonstrates the importance of keeping on top of hyperthyroidism. Hyperthyroidism increases risk but everyone has an underlying risk.
Too high for what ? There is no way for anyone to answer that question with the information available at the moment. No one can tell anyone if 'x' is too much. We don't even know for sure if there's a problem at all, we were just discussing recently found information that a receptor that T4 uses has some connection to cancer 'proliferation'.
If you mean from a cancer risk the T4 risk is linear, higher T4 levels give higher risk. This is relative since we all have T4, natural unless the thyroid packs in. Studies are a little inconsistent but generally show higher risks with higher T4 levels even when T4 is within its reference interval. I will cite the studies in my write up.
From a hypothyroidism treatment viewpoint an fT4 of 19 or 20 would usually be considered ideal if you are feeling well.
Not to confuse anyone Jim. Just add my husband had high T4 (not on any treatment) and slightly above range full blood count (polycythemia Vera) Until prostate cancer diagnosis . The hormone treatment he is on has brought T4 under range at 10 -12-24 range ( private test due to tiredness) .
T3 was 5 in range ! and his full blood count also to the very bottom in range result in test at hospital.
I wonder what part those high levels played, in his case, driving the PSA up to 68 !
I guess thyroid hormones can drive other activities that are good or bad but I don't know anything about their potential effect on PSA. Cancer and its treatment can affect thyroid hormone levels which is why I'm being careful to only look at studies that determine thyroid status a few years before cancer diagnosis.
I would really like to know more. I was placed on Levothyroxine back December 2012 and nearly immediately felt sx of hyperthyroid at the time it felt like how they describe people on amphetamines! I was alarmed and called the doctor's office and was told "You need to get used to feeling normal" . Admittedly I was a bit over weight, but I felt well, walked 2 miles a day 3 times a weeks. My BP and pulse had always been that of an athlete! I was a sprinter many years ago in high school nearly never ate any kind of fast food. We were living with a lot of business stress after 12 years of intense and difficult senior care. I was dx on an annual physical using a TSH which I was never given the number. I was taken by surprise since I had not noticed any symptoms of hypothyroid . Having been schooled not to play your own doctor I trusted even though it made zero sense. With in a years time I was dx with low grade hypertension and placed on 5 mg each of Lisinopril and Amlodipine. After 4 3/4 years of feeling like hell and our situation changing I decided to make a bold move to wean myself off Levothyroxine of course I did notify the doctor and also the amlodipine. I stayed on the lisinopril not wishing to create more problems for myself . Many of the horrible effects of Levothyroxine have disappeared, but I am concerned about lingering problems I may not be aware. Your post interested me given what has become crystal clear to me about my now former doctor's obsession with Cancer and keeping everyone's BP 90/50 may well have jaded his approach to care of health. What do I need to be concerned about? Appreciate an honest answer
I've added a separate comment at the end of this post with a link to my more recent post which goes into more detail and gives the evidence. If you were given levothyroxine and didn't need it apart from making you ill for quite some time I don't think it will have done you any permanent harm. It might have increased your risk of cancer but that is in the past.
I would put in a request for all your thyroid function test results, GP surgeries have to provide this. I would also consider getting a private blood test and posting the results on this forum. Here is a list of tests thyroiduk.org/help-and-supp... . I use the Monitor My Health one because it is done by an NHS lab and is the cheapest.
This post is superseded by my more recent post healthunlocked.com/thyroidu... which refers to my ibshypo website which gives a detailed discussion along with the evidence.
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Low T4 result being on T3 only
