Iron Deficiency May Predict Greater Risk for Hypothyroxinemia: A Retrospective Cohort Study of Pregnant Women in China

[helvella]

One of the parts of the thyroid jigsaw that is most often repeated here is the importance of iron levels. Here, in the context of pregnancy, another paper highlighting the importance of adequate iron. Yet, most of the time, we hear of standard treatment being ferrous sulphate - and the difficulty people have in taking it.

Thyroid. 2018 Jul 3. doi: 10.1089/thy.2017.0491. [Epub ahead of print]

Iron Deficiency May Predict Greater Risk for Hypothyroxinemia: A Retrospective Cohort Study of Pregnant Women in China.

Teng X1, Shan Z2, Li C3, Yu X4, Mao J5, Wang W6, Xie X7, Du J8, Zhang S9, Gao Z10, Zhang X11, Li L12, Fan C13, Teng W14.

Author information

Abstract

Background

Pregnant women are highly vulnerable to iron deficiency (ID) due to the increased iron needs during pregnancy. ID decreases circulating thyroid hormone concentrations likely through impairment of iron-dependent thyroid peroxidase (TPO). The present study aimed at exploring the association between ID and hypothyroxinemia in a retrospective cohort of pregnant women in China.

Methods

To investigate the relationship between ID and hypothyroxinemia, we retrospectively analyzed 723 pregnant women in the present study, including 675 and 309 women in the second trimester and third trimester, respectively. The trimester-specific hypothyroxinemia was defined as free thyroxine (FT4) levels below the 2.5th percentile of the reference range with serum thyrotropin (TSH) levels in the normal or higher than the 97.5th percentile of reference range in each trimester of pregnancy. Serum TSH, FT4, thyroid peroxidase antibodies (TPOAb), thyroglobulin antibodies (TgAb), serum ferritin (SF), soluble transferrin receptor (sTfR), and urinary iodine concentrations (UIC) were measured. SF, sTfR, and total body iron (TBI) were used to indicate the nutritional iron status.

Results

Cross-sectional multiple linear regression analysis showed that iron status was positively associated with serum FT4 levels in the first and second trimesters of pregnancy, but not in the third trimester. Logistic regression analysis showed that ID was an independent risk factor for hypothyroxinemia (odds ratio [OR] = 14.86, 95% confidence interval [95% CI] = 2.31-95.81, p = 0.005 in the first trimester and OR = 3.36, 95% CI = 1.01-11.21, p = 0.048 in the second trimester). The prospective analysis showed that pregnant women with ID during the first trimester of pregnancy had lower serum FT4 levels and a higher rate of hypothyroxinemia in the second or third trimester than those without ID.

Conclusions

ID appears to be a risk factor to predict hypothyroxinemia in the first and second trimesters of pregnancy, but not in the third trimester. We suggest that pregnant women with ID in the first and second trimesters be regarded as a high-risk group for maternal hypothyroxinemia.

PMID: 29968513

DOI: 10.1089/thy.2017.0491

ncbi.nlm.nih.gov/pubmed/299...

[Ari3]

What are normal iron levels uk range please?

[helvella Administrator in reply to Ari3]

As with almost all tests, the ranges vary by lab. There are a mixture of good and bad reasons for this, but vary they do. It is, therefore, inappropriate to use ranges other than those for the lab.

[fluffyhat in reply to helvella]

Very interesting, I couldnt see what they said about the difficulty of taking ferrous sulphate tho as I could only see the abstract even when clicked on full article. I have just completed 2 mos of oral iron for very low ferritin - feeling much better for it and my thyroid function blood test have improved which has sold it to me..my GP wants to retest iron levels in 3 mos saying if they have dropped then wld need to investigate why. I am reluctant to go 3 months without even over the counter iron as it affected my day to day life massively. Does being hypothyroid cause iron deficiency I wonder ? In which case that would explain my low levels as I dont have any symptoms or potential risk factors.

[crimple in reply to fluffyhat]

I always suffered with low iron until I went on a gluten free diet. I think gluten destroys the guts capacity to absorb iron properly, but that is only my opinion/ anecdotal evidence! MY Dad has Crohn's and all they ever give him for his very low iron is ferrous sulphate which is pretty useless with nasty side effects. I think a lot of people would have better health without gluten, but thta's only my opinion!

[eeng in reply to crimple]

It is well established that being coeliac makes it very difficult for the gut to absorb iron, so in people with gluten intolerance (which is probably just a mild form of something akin to coeliac that doesn't show up on the tests) you would probably expect iron absorption to be a problem.

[fluffyhat in reply to eeng]

Many thanks, I have been gluten free for a few weeks and plan to cont !

[Ari3 in reply to fluffyhat]

Could u post me ur results with ranges of u don’t mind for iron and ferritin before and after so I could compare with mine thank you

[fluffyhat in reply to Ari3]

Pre iron; ferritin 18 (15-200), Hb 145 (115 - 160).

After iron : ferrtin 43 and Hb 154,

Also free T3 rose as well ( without any change in levo dose.

Should say I did only take 6 weeks out of the 8 week course ferrous fumarate..so I still have some keft for a rainy day.

But plan to supplement with one of the low dose over the counter iron tabs but eat liver once a week and cont with gluten free eating.

[Ari3 in reply to fluffyhat]

What do you think of spatone original iron sashes? Are they any good to boosted iron levels?

[Angel_of_the_North in reply to Ari3]

They work for some people, but are very low dose and so are an expensive way to raise levels.

[Ari3 in reply to Angel_of_the_North]

So is it ok for me to use 3 sachets a day?

Which iron is the best with less fillers and non constipated?

[Angel_of_the_North in reply to Ari3]

Really don't know. I just get ferrous fumarate off ebay and take with vit C.

[Ari3 in reply to Angel_of_the_North]

I managed to get spatone original from my GP

[Angel_of_the_North in reply to Ari3]

One ferrous fumarate tablet = about 12-15 spatone sachets

[Ari3 in reply to Angel_of_the_North]

Does it not make u constipated

[Angel_of_the_North in reply to Ari3]

No. But everyone is different.

[crimple]

Another little piece of the jigsaw, thanks Helvella. My iron levels improved once I was gluten free! Would that be considered anecdotal evidence? lol