hi again Mint ,
Yes , I can see it is a bit of a conundrum. However , applying Occam's Razor , ( the simplest explanation for any phenomenon should be preferred over more complicated explanations.. ! ) .
NOW , You have found that supplementing with 4000 IU per day , helped you , it reduced your symptoms. When you stopped that regime , and moved to a lower dose regime , the symptoms came back.
I would have thought that the obvious thing to do , would be to go back to 4000 IU per day. See if that helps. IF in 2 to three months time it hasn't helped , then take another course of action . Don't stop Vitamin D supplementation , just because your level is 79nmol/L . As I have explained above in this thread, imagine your body has compartments of vitamin D , which are continuously being filled , and continuously being emptied , as you use up your vitamin D . Cells require vitamin D , day to day , to perform their normal natural functions. If you are ill , or have a trauma of some kind for example , you will need even more , as those cellular functions need to be switched on , or cell behaviour needs to be modified. Simply absorbing calcium from your food will require a daily amount from your store of vitamin D.
See my bucket analogy up above in this thread.
Of course , there may be other reason why you have your symptoms, so as nettle says, it might turn out that you have another problem, such as thyroid , maybe B12, maybe folate. If you do look at these things , try to ensure you get a full investigation , i.e not just a quick look at TSH , for thyroid. The TSH hormone is not even a product of the thyroid gland , it is a pituitary hormone , you should look at t4 t3 and thyroid antibodies as well.
That pamphlet you have read , saying that 79 does not need supplement , is not looking at YOUR situation. You have been on supplements , because your level was as low as 11 , therefore you needed treatment. So, now you are in the midst of treatment , and your level has been measured at 79 , it was probably quite a bit higher when you were on 4000 IU, hopefully above 100 . When you stopped 4000 IU , then your level probably dropped to 79 , and is now on its way down. You must not look at any blood level as fixed , and never to change. The key point is that you need , Vitamin D supplement , at the rate that your own metabolism requires. It seems to be above 1500, and probably just a bit below 4000 IU per day.
In order to satisfy yourself that you are not overdosing , then I would suggest you get your calcium level measured , in a couple of months. Almost certainly , it will be normal. IF it is not , and that's very unlikely , then you should consider what to do. IF and only IF , it is above normal, then there is a chance you might have hyperparathyroidism. The fact that your Vit D level was originally 11 , is likely to mean there is something about your lifestyle, or your genetics,or your ability to absorb , or many other factors i.e smoking ? etc , which might possibly hinder developing a satisfactory Vit D level.
When you realise that , the human body over millions of years , used to spend lots of time , outside , in strong sunlight , creating 10,000 to 20,000 IU of vitamin D , per day throughout our evolution (in Africa) , and it is only comparatively recently , that we have stopped that. Then doses like 4000 IU are not excessive. In fact as mentioned above , the National Academy of Sciences , - Institute of Medicine , in the US , has said it is perfectly safe for a healthy adult to utilise that dose. Modern day outdoor workers , lifeguards etc that replicate those conditions , they have blood levels of vitamin D in the range 120 -140 and sometimes quite a bit higher. IF you get to those levels , and stay there , then you are giving your body the chance to fight off , or repair , any problems that may have arisen due to low Vit D. Make no mistake , a level of 11 was likely to cause all sorts of malfunction. In children , it would be rickets and more. In adults, then bone pains , muscular weakness, etc. immune system malfunction etc.
In a way , you have been lucky , many people struggle with levels like 20 - 30 - 40 , for years and years, not knowing , and just accepting the consequences , thinking it is just normal, or old age , etc .... You can do something about it. It is only in the last few years that the true extent of Vit D insufficiency and deficiency has been realised , and the effects on our bodies. Scientific and medical research is progressing at quite a pace. recommendations are slowly changing.... too slow for my liking ...!
Best of luck ,
Get back to me if you have any more questions.
BTBH.