Vitamin D deficiency and the rise of thyroid disease

What is vitamin D?

Vitamin D is naturally present in very few foods and usually available as a dietary supplement. Our body can produce vitamin D when UV rays trigger its production in the skin. All of vitamin D is not active, and in order to become active it needs to be processed by our liver and our kidneys. At the end of that process we have an active form of vitamin D, called calcitriol (1).

Vitamin D maintains balance of minerals such as calcium, iron, magnesium, phosphate and zinc. Up until recently it was thought vitamin D acts on preserving bone health, but the recent research has demonstrated that it may also play a role in many hormonal diseases, autoimmune diseases as well as cancer (2).

Why do people lack vitamin D, and what to do about it?

Depending on your genes, diet, supplementation and sun/UV exposure vitamin D levels in your body will change.

Although some promising indications have shown vitamin D can help when taken as a supplementary treatment for some autoimmune diseases, it is still unclear if there is a real benefit for autoimmune thyroid disease.

In the US, vitamin D supplements are recommended only for the treatment of conditions caused by the lack of vitamin D (2,3).

Vitamin D deficiency is defined by the US Endocrine Society guideline as less than 20 ng/ml (50 nmol/l), and vitamin D insufficiency between 21 and 29 ng/ml (2,4).

Vitamin D2 or vitamin D3 supplementation can be used if you are low on vitamin D, it might take about eight weeks of treatment to reach the recommended blood levels of vitamin D (4).

How much of vitamin D is safe?

According to the US Endocrine Society guideline, all adults require 600–800 IU (15–20 µg) daily dietary intake of vitamin D.

The upper cutoff to minimize the risk of adverse effects is 100 ng/ml (250 nmol/l) vitamin D (4).

Recommended Dietary Allowances for vitamin D are:

0–12 months → 400 IU (10 mcg)

1–70 years → 600 IU (15 mcg)

>70 years → 800 IU (20 mcg)

Vitamin D, underactive thyroid and Hashimoto’s

Vitamin D is responsible for anti-inflammatory reaction of our immune system (5–7). Hashimoto’s and an underactive thyroid is one of a few conditions where vitamin D levels were found to be lower compared to the general population (8).

One of the suggested mechanism connecting vitamin D and Hashimoto’s is through small proteins called cytokines. Cytokines are produced by our own immune cells, and help in communication between different cell types in the body, and many of them are very active during the inflammation (e.g. when virus or bacteria attacks us, or when we get injured). Vitamin D blocks cytokines and through that it prevents inflammation. Lack of vitamin D will not prevent inflammation and can trigger Hashimoto’s, followed by development of hypothyroidism (9).

Research has several hypotheses on how is vitamin D deficiency connects to Hashimoto’s and hypothyroidism:

1. Vitamin D deficiency is one of the environmental triggers (9).

2. Low blood levels of vitamin D will contribute to worsening of health (10).

3. Benefit of vitamin D - administration of high doses of vitamin D may prevent autoimmune diseases (11).

Hashimoto’s is characterized by a loss of immune balance, which results in an underactive thyroid. It is caused by genes and environmental triggers, and one of these triggers is vitamin D deficiency.

However, the link between Hashimoto’s and vitamin D levels are not fully researched and understood. So far studies have conflicting results. The problem might be that there is a multitude of contributing factors, such as smoking, alcohol, selenium, iodine, stress, infection, medications and many more (12–14).

Some of the research has shown that variations in four different genes are responsible for the likelihood of developing autoimmune thyroid disease, and are at the same time connected to vitamin D function (15–17). However, not all of the research has confirmed all the results (18–21).

Research has looked into the direct role of serum vitamin D levels in autoimmune thyroid diseases, but the results are still controversial: while some studies have found lower levels of vitamin D in patients suffering from autoimmune thyroid diseases, the other ones did not find enough evidence for such a claim (9,22–24). All of the studies were geographically limited, which perhaps offers a very simple (and a naïve) explanation for the confusing and conflicting results. The question remains: in what way vitamin D impacts thyroid disease, and can it’s levels be a good indicator for the stage or progression of the disease?

Conclusion

It very much seems that the research data on the role of vitamin D in autoimmune thyroid diseases are not complete, and the mechanism is not fully understood.

Partial blame for this is on the research study design: small number of participants or the fact the data has been collected at one point only, making it difficult for participants to remember many of the past events.

Also, research has to take in consideration the impact of different geographies, seasons, weather conditions, daily sun exposure, BMI, nutrition and heterogeneity of the sample.

Lastly, perhaps there is some true to the power of vitamin D in treating Hashimoto’s. We do need larger, cleaner and more inclusive data to test this hypothesis. Even when we go global in the research, we might see vitamin D works for a sub-group of Hashimoto’s patients better than for the others. Whatever the results will be, we will learn something beneficial for all of us all over the globe.

References

1. Dietary Reference Intakes for Calcium and Vitamin D The National Academies Collection: Reports funded by National Institutes of Health, 2011

2. Muscogiuri G, et al. Vitamin D and thyroid disease: to D or not to D? 2015

3. Kennel KA, et al. Vitamin D deficiency in adults: when to test and how to treat, 2010

4. Holick MF, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline, 2011

5. Aranow C. Vitamin D and the immune system, 2011

6. Prietl B, et al. Vitamin D and immune function, 2013

7. Antico A, et al. Can supplementation with vitamin D reduce the risk or modify the course of autoimmune diseases? A systematic review of the literature, 2012

8. Adorini L. Intervention in autoimmunity: the potential of vitamin D receptor agonists, 2005

9. D’Aurizio F, et al. Is vitamin D a player or not in the pathophysiology of autoimmune thyroid diseases? 2015

10. Kriegel MA, et al. Does vitamin D affect risk of developing autoimmune disease?: a systematic review, 2011

11. Schwalfenberg GK, et al. Solar radiation and vitamin D: mitigating environmental factors in autoimmune disease, 2012

12. Effraimidis G, et al. Mechanisms in endocrinology: autoimmune thyroid disease: old and new players, 2014

13. Hasham A, et al. Genetic and epigenetic mechanisms in thyroid autoimmunity, 2012

14. Tomer, Y. Mechanisms of autoimmune thyroid diseases: from genetics to epigenetics, 2014

15. Mazokopakis EE, et al. Hashimoto’s autoimmune thyroiditis and vitamin D deficiency. Current aspects, 2014

16. Muscogiuri G, et al. Mechanisms in endocrinology: vitamin D as a potential contributor in endocrine health and disease, 2014

17. Feng M, et al. Polymorphisms in the vitamin D receptor gene and risk of autoimmune thyroid diseases: a meta-analysis, 2013

18. Lin, W. Y. et al. Vitamin D receptor gene polymorphisms are associated with risk of Hashimoto’s thyroiditis in Chinese patients in Taiwan, 2006

19. Stefanic M, et al. Association of vitamin D receptor gene 3'-variants with Hashimoto’s thyroiditis in the Croatian population, 2008

20. Yazici D, et al. Vitamin D receptor gene ApaI, TaqI, FokI and BsmI polymorphisms in a group of Turkish patients with Hashimoto’s thyroiditis, 2013

21. Maalej A, et al. Lack of association of VDR gene polymorphisms with thyroid autoimmune disorders: familial and case/control studies. J Clin Immunol 28, 21–25, doi:10.1007/s10875–007–9124–9 (2008).

22. Orbach H, et al. Vaccination infection and autoimmunity: myth and reality VIAMR 2005–10–26–28, Beau-Rivage Palace Hotel, Lausanne, Switzerland, 2007

23. Goswami R, et al. Prevalence of vitamin D deficiency and its relationship with thyroid autoimmunity in Asian Indians: a community-based survey, 2009

24. Effraimidis G, et al. Vitamin D deficiency is not associated with early stages of thyroid autoimmunity, 2012the