The link between vitamin D and hypothyroidism and Hashimoto’s

Research has shown that there is a strong link between vitamin D and hypothyroidism.  Let’s have a look at what it means if you have an underactive thyroid or Hashimoto’s Thyroiditis.

Today I want to look at vitamin D and what vitamin D deficiency means for hypothyroid and Hashimoto’s patients.

I was diagnosed with Hashimoto’s Thyroiditis in 2015, but it wasn’t until 2018 when the endocrinologist I went to see tested my vitamin D levels. Needless to say, my vitamin level was below 20 ng/ml (nanograms per mililiter).

Functional medicine leaders recommend (1) that vitamin D levels should be between 60 to 80 ng/ml, which is what my functional medicine doctor also confirmed.

So why is vitamin D so important for our health? And why, if you have an underactive thyroid or have Hashimoto’s, should you check your vitamin D level?

What the research found

Well, let’s start off by why vitamin D is important. A 2011 study (2) stated that “Vitamin D can modulate the innate and adaptive immune responses. Deficiency in vitamin D is associated with increased autoimmunity as well as increased susceptibility to infection.”  Vitamin D is important for our immune system to function optimally.

Second, a study (3) found that hypothyroid patients have significantly lower vitamin D levels compared to the control group. It was a small sample group (30 hypothyroid patients and 30 healthy subjects), yet the results were important.

The implication is that if you have hypothyroidism or Hashimoto’s, you probably have low levels of vitamin D.

Should you take a vitamin D supplement?

So, what are the effects of taking vitamin D when you have an underactive thyroid?

Luckily, there was a study published in 2018 (4) that looked at exactly this. The study was a randomized double-blind, placebo-controlled trial, where 201 hypothyroid patients were studied. Some of the subjects were given 50,000 IU of vitamin D supplements, and the others were given a placebo for 12 weeks. What did the researchers find?

After the 12 weeks, those patients who took the vitamin D supplement had a significant increase in their blood serum levels and a significant decrease in TSH levels. The researchers stated that there are two mechanisms that may explain why vitamin D is low in hypothyroid patients.

First, the vitamin D is poorly absorbed in the intestine, and second, the vitamin D is not activated properly in the body.

The same study mentioned another study where autoimmune thyroid patients were given 60,000 IU vitamin D weekly, and it led to a significant reduction in TPO antibodies.

Vitamin D can help to lower TPO antibodies

Another study published in 2019 (5), looked at 130 patients who have been diagnosed with autoimmune hypothyroidism.  The researchers wanted to investigate the link between vitamin D and vitamin B12 and how it correlates to the TPO antibodies.  

What did they find?

They found that “vit-B12 deficiency and vit-D deficiency were associated with autoimmune hypothyroidism“, and more importantly, that there was a negative correlation between vitamin B12 and vitamin D levels and the TPO antibodies in these patients.  That means, that the higher the vitamin B12 and vitamin D levels, the lower the TPO antibodies were.  

Before you start supplementing with vitamin D

Before you start supplementing with vitamin D, please do a blood serum test first. Vitamin D is fat-soluble, which means that whatever you ingest, stays in your body. You don’t want to risk overdosing on vitamin D, as that has other serious health consequences.

Wrapping it up

The research that is currently available shows that there is a strong link between high vitamin D levels and low thyroid antibodies.  Other research also found that taking a vitamin D supplement helped to lower TSH levels.  

But before you start taking vitamin D, please remember that it is a fat-soluble vitamin, and it will stay in your body.  So please speak with your doctor first and get a blood test done first to see if your vitamin D levels are too low.  

Only then, should you take a vitamin D supplement.  


  1. A Functional Medicine Guide To Supplements, Dr Will Cole,, accessed 29 April 2022
  2. Vitamin D and the Immune System. 2 March 2011. Journal of Investigative Medicine., accessed on 29 April 2022.
  3. Vitamin D Deficiency and Its Association with Thyroid Disease. 7 November 2013. International Journal of Health Sciences., accessed 29 April 2022.
  4. The Effects of Vitamin D Supplementation on Thyroid Function in Hypothyroid Patients: A Randomized, Double-blind, Placebo-controlled Trial. Sept-Oct 2018. Indian Journal of Endocrinology and Metabolism. Accessed on 29 April 2022.
  5. Vitamin B12 and Vitamin D Levels in Patients with Autoimmune Hypothyroidism and Their Correlation with Anti-Thyroid Peroxidase Antibodies.  Accessed 09 May 2022
Adele du Rand

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