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Vitamin D levels correlate with increased FT3 levels

Interesting that TSH and FT4 show no significant association with vitamin D, but FT3 does. Certainly shows yet another way in which TSH is not perfectly correlated to thyroid hormone levels.

LURIC: Vitamin D levels correlate with increased FT3 levels

May 17, 2015

NASHVILLE, Tenn. — A significant association was found between serum 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D and increased free triiodothyronine levels, according to study findings presented here.

However, no significant association was found between vitamin D levels and thyroid-stimulating hormone (TSH) or free thryoxine (FT4), according to researchers.

“Accumulating evidence suggests a complex interplay between thyroid hormone status and vitamin D,” the researchers wrote. “Previous studies showed that thyroid hormone inhibits 25-(OH)D 1-alpha hydroxylase and that vitamin D suppresses TSH secretion and exerts direct effects on thyroid cells such as [in the] inhibition of iodine uptake. Clinical data on direct effects are, however, sparse and partially controversial.”

Anette Merke, MD, of the Thyroid Center Bergstrasse in Germany, and colleagues evaluated 2,804 participants (mean age 62.8 years; 30% women) from the Ludwigshafen Risk and Cardiovascular Health (LURIC) Study to determine if serum 25-(OH)D and 1,25-dihydroxyvitamin D (1,25-(OH)D) is linked to TSH, FT4 and free triiodothyronine (FT3) levels. All patients were referred for angiography.

Linear regression analysis was performed for TSH, FT4 and FT3; adjustments were made for age, sex, BMI and active smoking status.

Although no significant association was found between vitamin D levels and TSH or FT4, a significant association was found for serum 25-(OH)D and FT3 (P = .043) and serum 1,25-(OH)D and FT3 (P < .001).

“The mechanisms by which thyroid hormones influence vitamin D metabolism is still unknown,” the researchers wrote. “Thyroid hormones, ie, FT3, exert their actions by binding to thyroid hormone receptors, which belong to the nuclear receptor superfamily including the vitamin D receptors; polymorphisms in the [vitamin D receptor] gene have been associated with autoimmune thyroid disease. The reason for the close relationship between FT3 and vitamin D remains speculative. To our best knowledge this is the first [study] to report a correlation between FT3 and vitamin D levels.”

According to the researchers, more studies are needed to fully comprehend the pathophysiological systems of the association between metabolites. – by Amber Cox


Merke A, et al. Abstract 1085T. Presented at: AACE 24th Annual Scientific & Clinical Congress; May 13-17, 2015; Nashville, Tenn.

Disclosure: The researchers report no relevant financial disclosures.


Ludwigshafen Risk and Cardiovascular Health (LURIC) Study

22 Replies

Okay, I must be exceptionally stupid but what does this mean?


You are not stupid. It just means that they have found that there is a correlation between vitamin D levels and free T3 levels but they don't yet know why. I find it quite interesting because so many thyroid patients seem to have problems with vitamin D and people with vitamin D deficiency often feel like they have hypothyroidism. This could be quite significant. If only we knew what the link was!


But Carolyn it doesn't say that. You are saying that vit. D deficiency 'feels' like hypo. But vitamin D deficiency is not always associated with being hypo.


I know it doesn't say that. I'm just saying that it could be significant because many people with hypothyroidism also experience vitamin D deficiency. I know that vitamin D deficiency isn't always associated with hypothyroidism, and I didn't claim it was, but sometimes it is and maybe this correlation is an indication of some link between them.

I know this paper is far from conclusive but it raises some interesting questions. Hopefully scientists will investigate this apparent link further. Maybe there is no link; who knows? It is just interesting to me and some others. Maybe it isn't of interest to you and that is perfectly fine :)

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Carolyn, I was trained a long time ago to not speculate.

This paper, based on how much is available in the abstract is not only far from conclusive, it is entirely uninformative. It's like 'click bait'.


You were trained not to speculate, Gabkad? Who did that awful thing to you? Shoot them!


Yeah, Chancery. Legal training. Hard to unlearn some things. Shooting would land me in prison. I think I'll have to pass. ;)


I don't know, a terrible wrong has been done you. I reckon there's a case for both provocation and mitigating circumstances!


Since I'm not a novelist, probably I'm okay.


I'm with you here gabkab.

The article doesn't seem to say what the association is, even if it is positive or negative. The nature of the association is the key surely.


sandi, exactly.


Helvella, I read a study (sorry no link) some while ago which suggested good levels of vitamin D aids conversion of T4 to T3. The study above is saying that FT3 influences vitD?


I think the study just shows there is a correlation between vitamin D and FT3 levels. I don't think from the result you can really infer whether FT3 is affecting the vitamin D levels or vice versa.




Or in fact, there could be no link at all - some other unknown processes could be behind the trends in both vitamin D and FT3.


Hypohim, thank you, feeling rather 'what's that all about then?' tonight. :)


Like gabkad I was struggling with this one,however,for what it is worth .....I can confirm that as one who now has T3 added to T4 ,at my last Endo visit he was questioning what his medical student knew about the importance of Vitamin D?.....bone strength was obviously discussed and as one who continually complained to my GP about joint and muscle pain for years whilst I was only prescribed 50mcgs T4 I often wonder how much damage was done for that 10 yrs before my Endo did my FT3 test .

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My apologies if anyone thought there was an answer present in my post. No, there isn't.

The abstract refers to a complex interplay between thyroid hormone status and vitamin D. Which certainly is NOT a claim that vitamin D causes any change in FT3, nor that FT3 causes any change in vitamin D. It also does not claim that they do not cause those changes.

It is, quite simply, an observation. Well, the summary from numerous individual observations.

My introductory remark was formulated with full recognition of the limitations - and was directed very specifically at one factor: That TSH is yet again shown to be somewhat more decoupled from thyroid hormone levels than is usually accepted by the medical establishment. A perfect reflection of thyroid hormone levels by TSH would have shown TSH reducing. Non est perfecta speculo.

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Helvella, got the first bit but had to go to Google Translate for speculo. Not a perfect mirror at all.


it says "previous studies showed.......vitamin D suppresses TSH secretion" & apologies for the out of context statement...

personally, as a guinea pig - my high range TSH corresponded to low vit D and changing seasons...

Q aren't we supposed to be more active summertime with more hours of light?

eorum latinas non sumus british - or text speak!!! lol!


Well, what a confusing puddle !

Part of this large study's conclusion conflicts with earlier findings:

"“Previous studies showed that thyroid hormone inhibits 25-(OH)D 1-alpha hydroxylase and that vitamin D suppresses TSH secretion . . . . " and these previous studies match my personal experience of TSH falling to a LOWER, healthier level (around 1.0) when a "vit D" deficiency was identified and corrected.

The main finding of the study could read like there is a correlation btw the 2 active "vit D" metabolites (25, and 1,25 . . . ) and FT3, implying the higher the former, the higher the latter in serum, OR SUCH which would be verified by the data presented - this being "a significant association".

Perhaps given the venue at which the findings were delivered, someone will come up with apt Country & Western lyrics to explain its true meaning, or reasonable interpretations and its apparent contradictions with earlier studies . . . . . thereby clarifying the muddied waters. (Is Kenny R still alive ? ?)

Maybe we can have a thyroid awareness week concert & invite crooners of such informative ( . . . . and hopefully amusing) songs.

Isn't it INTERNATION THYROID AWARENESS WEEK, any time soon ? ? ?

Take care all !


Well I, for one, am frightfully excited that there is an association between T3 and Vitamin D. As someone who recently discovered that her Vitamin D was through the floor, despite having supplemented it for 5 months, I am happy to clutch at any straws.

I will now take this information and speculate wildly, and then, hopefully, come up with a working theory with which I can annoy my doctor. It's what I do...

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