Could a magnesium deficiency cause mild hypothyroidism?

Hi I've been having low thyroid problems for over a year now. The highest my tsh has ever been Is 5.7,but my t4 and t3 have always been optimal. I've been tested for hashimotos twice and both came back negative. The doctors don't know what's causing my thyroid to stop working properly. Last year I took multivitamins as I felt it may have been a nutritional problem and after 3 weeks my tsh came down to 2.1 and all of my symptoms disappeared. So I stopped the vitamins and after a month it went back up to 5.1. I tried taking the vitamins again but they didn't work. So for the last few months I've been searching for the specific vitamin that could be causing my problems. I just had my serum magnesium tested (I know this isn't the best test but it was all I could get on the nhs) and it came back at 0.77 which from what I've read is pretty low,and to be honest since only 1% of mg is in your blood I'm probably very deficient. I've had a look online at mg deficiency and hypothyroidism and there does appear to be a link. Has anyone heard of this or experienced this before?

Thanks in advance.

I don't have a range (I forgot to ask) however I've copied this from Wikipedia......

Normal magnesium levels in humans fall between 1.5 - 2.5 mg/dL. Usually a serum level less than 0.7 mmol/L is used as reference for hypomagnesemia

One more thing to add: the multivitamins I was taking only had 27% of my RDA for mg,I've read online that if you have a severe deficiency multivitamins will only work a little bit ( this could be why they didn't work the second time) has anyone heard of this?

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12 Replies

  • The RDA of magnesium is 300mg for men and 350mg for women. Most of us are probably magnesium deficient unless we supplement. You'll know if you're oversupplementing because you'll have diarrhoea. I wasn't aware that magnesium deficiency could affect TSH, though.

    Have you been tested for ferritin, vitD3, B12 & folate? Many of these are deficient or low in range in hypothyroid people.

  • Hi yes I've been tested for d3,b12, folate and ferritin all has came back fine. I do have symptoms of mg deficiency such as eye twitching and leg cramps. I thought I had a deficiency before I was tested as I just don't eat it in my diet,I've worked out on my good days I only get about a third of the RDA. I may have to invest in a red blood test to get a better picture.

  • Hi thanks for your reply,you said that oestregon dominance can cause cortisol problems, does it cause it to go higher or lower? And I'm in my twenties so I should be pretty balanced hormone wise,I've had no problems with periods etc.

  • Hi my d3 came back at 76 (50-70)

  • Hi Magnesium is a very tiny range, So if in range, only improve it by food intake, as c an be dangerous, otherwise. It is involved with kidneys and heart as an electrolyte. They must always be in range The onl,ly very loose connection is Atrial Fibrillation, this can be brought on by thyroid disease,it would have happened any way but can cause an early on set. Then sometimes the Magnesium could be low. below range. In this case supplements from a doctor with weekly tests.

    Worth checking your calcium, potassium and sodium. All electrolytes too. potassium and sodium are in U`s and E`s, simple kidney function test.

    Best wishes,


  • Are you saying that too much magnesium can cause AF???

  • Hi Sorry if not clear. The blood result for magnesium ( although not perfect) needs to always be in range. If low in range, only safe to take it in food. Supplements as described , magnesium oxide best,only suitable from GP or a doc etc if below range.. Too high dangerous and too lw, so long as in range , fine. We often feel we do need more, but then in food , that is fine and safe.


  • I slightly disagree in terms of supplements. As you say, blood magnesium levels are almost always in range, as it is so important.

    But your body will take from the cells to achieve this, leading to a cellular deficiency requiring supplementation, even when you have normal blood levels.

    I base this on my own experience. Low normal blood levels, deficient red cell levels. I was told by my Consultant to take 150mg magnesium citrate daily. I also use a spray. I would have no qualms about increasing that dose up to say 300mg, depending on bowel tolerance. If you get the runs, you're on too much.

    Oh and my diet has plenty of magnesium rich foods in it, because I work hard on getting enough potassium (important when on B12 injections). Potassium rich foods are also usually rich in magnesium, and if ever there was an excuse to eat chocolate, this is it!

    So I would say if you can get a red cell magnesium test then that's a good idea, as you may well benefit from supplements. This is an example of the test I had done by Biolab:

    You say your other vits and mins tests came back fine - ferritin, B12, folate - but what were they?


  • I When I had my early Potassium cardiac arrests, the most lethal sort. My Magnesium was below range, blood test. My Cardio and nephrologist who I had been under many years, then put me on a dose of magnesium oxide. We had to increase it a lot until blood in range.I have it tested + U`s and E`s once or twice a week, three times a day in hospital. Still when I arrest I often have to have an IV again as then the tablets are not enough.However, if the magnesium after an arrest comes back OK, then a n IV too dangerous. It is an electrolyte all inter dependant, especially lethal Potassium.

    Best wishes,


  • I wasn't trying to suggest that a 150mg daily supplement was in any way comparable to an IV infusion, which I believe would contain several g's of magnesium administered at a rate of up to 150mg per minute. It's a completely different kettle of fish, and unsurprisingly dangerous if not needed.

  • Hi I was using that purely as an example to show how important the correct dose should be right.

    It is very different in cases of heart and kidney problems. Also they can happen without any warning. a doctor wanted me to take cortisone. I disagreed. It consequently turned out that because of my hart, that would have been lethal

    Unfortunately life is unpredictable so we just need to be careful.

    Best wishes,


  • I supplement with magnesium because I have osteoporosis , without it the calcium is not absorbed properly. From what I understand magnesium is not stored so if you consume more than needed your body will excrete it.

    It is a very important mineral .

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