I have posted many times and it was agreed going off 3 sets of blood tests that my low tsh low t4 and low t4 consistently would indicate secondary hypothyroidism or hypopituarism but one comment stood out when it was said that low body weight caused by a strict diet could cause hypothyroidism? is that the case as I'm a recovered anorexic/bulimic ( over 20 years recovered) but still maintain a slim body type by diet and exercise. does this mean all my low levels could be not my thyroid but my weight? as in ndt or thyroxine wouldn't help? ( I am waiting to change doctors to try yet again to be listened to and diagnosed) weight gain is still an issue plus all the other symptoms but as I've gained I've upped the exercise and dieted more...thank you
being low body weight causing secondary hypothy... - Thyroid UK
being low body weight causing secondary hypothyroidism??
Secondary hypo is a problem with the pituitary, rather than the thyroid itself, as I'm sure you know. For some reason, the pituitary isn't producing enough TSH to stimulate the thyroid - and that could also be due to a problem with the hypothalamus (tertiary hypo) not stimulating the pituitary. But, you can't know without further testing.
I have never heard that low-calorie diets can cause pituitary or hypothalamus problems - and a quick search revealed nothing. Low-calorie diets can cause low FT3, due to poor conversion. But, that is not your case because your FT4 is also low. So, without a lot more information, I wouldn't give the low-calorie theory too much credence.
Having said that, it's also true that anorexics often end up with hypothyroidism, due to the effect of low-calories on the thyroid itself. But, they usually have high TSH. So, it would appear that what you have is Central hypo (pituitary or hypothalamus problem), pure and simple. Such a shame that doctors are so ignorant they don't recognise this.
thank you for your response I didnt think it could as it never affected me when I was ill all those years ago and although I have a controlled diet I eat well and good foods but any excuse this new doctor can find I want to eliminate before I register there. I'm sure he'll use the usual...all tests are within range/its menopause/ its just stress.....this is my last ditch attempt before I try private with someone who knows their stuff...further down there is a comment that says low calorie diets do make your T4 and T3 go low so I'm getting two verdicts but I did hope it wasn't low body weight that causes it...thanks
Not really two verdicts, just two explanations that vary slightly in the way they're expressed. 
true
From my own experience of once being an in-patient for disordered eating (over-exercising & not eating enough), it really messed up my head and made me feel ill. I still exercise a lot but I eat more sensibly (high protein, low carb) as I want to keep and build on my muscle mass, as this increases metabolism and keeps my type 2 diabetes in check. I am hypothyroid (recently increased to 125mg) and peri-menopausal, like you. I have just started HRT last week. All in all, I feel great, despite being on array of meds but also think they are all necessary. I’m fortunate that I have a good GP who knows a lot about thyroid disease. He likes my TSH under 1, he changed me from Teva on his own and has started the HRT trial. I don’t know much about secondary hypothyroidism but from experience, I can say that over exercising and under eating will affect your mental health greatly and upset your metabolism and your hormones greatly. I hope this helps you in some way. BTW, I saw a post from you on coming off Zopiclone. I was 15mg as an inpatient and 7mg when I was released. It really should be for short term usage only. I stopped cold turkey after a few years and asked my GP to remove it from my repeats. It’s a very destructive medication as it affects the heart long term. If you want to talk more about anything, feel free to message me. x
Thank so much for your reply I'll pm you if I may and reply with a longer message as your life and past sounds very similar to mine. I dont over exercise I only walk 5 miles a day the rest is quite sedentary of an evening but anyway thanks very much I'll be in touch
Severe illness, depression or a very strict diet can reduce the quantity and quality of TSH secreted leading to low normal fT3 and fT4. This is not secondary hypothyroidism as both the pituitary and hypothalamus are healthy, they are behaving normally in these circumstances. It's possible that your previous anorexia has caused your hypothalamic pituitary axis to be reset, meaning your TSH stays lower than it should be (this is just a guess, I don't know of evidence it happens). If your current diet is very strict (low calorie) then it could also have this effect. I call this 'subnormal TSH secretion' because TSH is lower than it should be but it is not true secondary hypothyroidism. This can have devastating consequences, see my profile for details.
People with a low BMI have a little less T4 to T3 conversion than people with a high BMI. I don't think this is a relevant factor in your case.
thanks for your info and reply I'm a little confused as my first message seems to be that low body weight/low calorie diet doesnt affect the levels of T4 or T3 ....all my symptoms are that of secondary hypothyroidism and it runs rife in my family . I am the only one of normal body weight the 4 other family members that have/had it are very large but because I have been fobbed off now for 5 year saying all levels are in range when they are bottom of the range and under range I wanted to eliminate all possible excuses the new doctor could throw at me as in saying i'm slim so it could be causing a similar effect to hypothyroidism without the thryoid or pituitary being at fault as you mentioned. Also when you say 'devastating consequences ' that worries me alot what do you mean? thanks
Low body weight, i.e. has a small effect on fT3 and fT4 ratio. This is small and would not have much effect. Strict low calorie diets and no doubt anorexia do lower TSH, fT3 and fT4. Your TSH is too low for your low normal fT3 and fT4. I don't know if your previous anorexia (or distress associated with it?) has contributed to this, I just speculate that it could.
It drives me nuts that all doctors interpret TSH, fT3 and fT4 results as if they are independent, they are not, they are inter-depedent. Doctors will happily tell you that when the thyroid fails fT4 falls a little and TSH rises rapidly whilst fT3 remains normal. This is why they place reliance on TSH. They fail to realise that when fT4 AND fT3 fall but TSH has not jumped up high something is wrong. Low-normal TSH, fT3 and fT4 is not normal. This is not really central or secondary hypothyroidism. The pituitary is almost certainly healthy and other pitutary hormones are invariably normal. There are many reasons the hypothalamic pituitary thyroid axis can behave like this. The axis can be down-regulated because of a period of high hormone levels or due to depression or very low calorie diets. Since this is not true secondary hypothyroidism I call it 'subnormal TSH secretion'.
The effects can be way beyond what the numbers suggest, for complex reasons I describe in my website, leading to quite profound hypothyroidism. When I refer to 'devastating' I mean the effects on pateints' lives. I do not mean it is life threatening or anything like that, rather the consequences of substantial hypothyroidism.
so this type of hypothyroidism how is it treated is it treated the usual route and it still has to be diagnosed which is where I'm struggling because I'm still in their range? ( my long term eating will not change as it works for me keeps me at a steady ish weight and mentally in a better place) but with all the hypo symptoms and menopause thrown in my quality of life is pretty grim !
Quality of life being pretty grim is what I had in mind when I wrote of devastating consequences. Unfortunately, this form of hypothyroidism is not recognised which is why I gave it the term 'subnormal TSH secretion'. The term is occasionally used but I think we need to make it better known so that this syndrome is diagnosed and treated.
You will have to push quite hard and be firm to get a diagnosis. If you see a doctor I suggest you take someone with you for support, so that you are not fobbed off. It is NOT normal for TSH to be low normal if BOTH fT3 and fT4 are low normal.
I'm pretty sure you will need some liothyronine (L-T3) treatment because the subnormal TSH levels lead to reduced T4 to T3 conversion. However, it is very difficult to get liothyronine prescribed because of the cost (only expensive in the UK). Therefore, it would be best to take one step at a time, get a prescription for levothyroxine and push for liothyronine (if you need it) at a later date.
thank you...i won't get anywhere with nhs doctors they are adamanton their ranges and even when e are all low and one below range they stickto their stupid ranges. they don't take me seriously and blame menopause and stress bla bla bla on my symptoms it's not thyroid related end of..that's their constant diagnosis. Will I get more luck if I go private or will they not have heard of subnormal tsh? afterall my doctors didn't even know about hypopituarism.
As far as I know my research on subnormal TSH secretion is novel. Doctors may be aware that it exists but they haven't bother to figure out. what the effects will be and how the lowish fT3 reflects low cellular levels. Some private doctors are OK, ThyroidUK have a list of doctors.
when doctors think my levels are NORMAL and can't see an issue there I have no chance with anything out of the norm. I've got the list of doctors but some still don't really dig deep if you have something unusual....what is your personal opinion ?
Not sure how I can answer that question. I'm trying to push the research into a more rigorous and scientific direction but I'm just a patient. In general doctors are hopeless scientists (even the research ones). Consider the advances made in physics and compare it to the dismal progress in endocrinology. I also get the impression medical researchers are only interested in their own ideas and field, they are not genuienly interested in progress and not patient centered. There are exceptions such as the ThyroidUK advisors but these are few and far between.
From your own point of view, and other patients all I can suggest is that you prepare well and at a consultation describe the effects on your life (not your symptoms - the effects, this is easier to relate to) and be gentle but very firm that you want help. As they will have no idea how to help just tell them you want a trial of levothyroxine or liothyronine. I'd go for treatment not endless investigations. Not sure if I've understood your question but I've given an answer!
yes thsys great thank you. I get ignored by doctors and I'm not assertive but when I see a consultant I will take someone with me they can vouch for my life being grim health wise. would t3 not help or ndt? I've not heard of liothyronine is that only prescribed privately?
Liothyronine is T3, strictly referred to as L-T3 for technical reasons. It can be prescribed on the NHS by endocrinologists. Any doctor can prescribe it but guidance tends to insist on it being prescribed by an endo.
Depending on how much weight you lost while anorexic this link may apply
healio.com/endocrinology/bo...
Thanks for this link. I found it very informative.
I lost around 4 stone down to 5 stone but only teetered at that weight for around 4 years then maintained a good weight from then on through 2 healthy pregnancies. I only started to exercise in my early 40's when the menopause started and i started to gain weight quickly. But its not much i walk 5 miles and day that is all and i eat strictly but good foods
I made this post a while ago, which might help answer your questions:
Weight loss with hypothyroidism 
Weight loss means my weightgain whingeing is over (for the time being)!
Can’t lose weight: Hypothyroidism, Hashimoto’s. Extreme obesity.
Low body temperature 
