Although in many studies, the relationship between autoimmune hypothyroidism (Hashimoto) and Vitamin D deficiency was shown, no research has been performed on the evaluation of non-autoimmune hypothyroidism and Hashimoto and effect of vitamin D on their treatment.
Retrospective case–control study.
The patients with Hashimoto (n=633) and non-Hashimoto hypothyroidism (n=305), along with a control group (n=200) were evaluated.
Primary and secondary outcome measures:
25(OH)D level, T3 and T4 levels were studied and Anti TPO and Anti TG tests were performed. The results of vitamin D level were analyzed and interpreted using SPSS in terms of the cause of hypothyroidism (immune and non-immune).
The results of the study showed the significant relationship of vitamin D deficiency with both immune and non-immune Hashimoto’s thyroiditis (HT). In vitamin D-deficient women, TGAb level was significantly higher than women with sufficient vitamin D. Women with lower vitamin D levels needed to increase the dose of levothyroxine.
Finally, the results indicated that non-autoimmune hypothyroidism, as well as HT, is associated with vitamin D deficiency. In addition, the serum level of vitamin D is effective in determining their treatment and the effect of levothyroxine.
Strengths and limitations of this study:
- The strengths of this study is the large sample size.
- This is the first study reporting the association of non-autoimmune hypothyroidism and vitamin D deficiency. The levothyroxine therapy outcomes are affected by vitamin D level.
- The differences of participants disease stage were the limitation of the study.
Vitamin D receptors exist in many body organs. Through these receptors, vitamin D has various functions, including the regulation of ion homeostasis, cell growth, cell differentiation, and cellular immunity . Vitamin D plays an important role in preventing the occurrence of many inflammatory diseases, infections, and autoimmune diseases . In numerous studies, the relationship between vitamin D deficiency and a variety of diseases, including musculoskeletal , cardiovascular , kidney disease , diabetes  and infections  had been shown. The thyroid gland is also one of the organs that have a receptor for vitamin D. The vitamin D receptor in the thyroid is a member of a large group of receptors called nuclear receptors, which also belong to the thyroid hormones receptor . Some studies indicated that vitamin D deficiency is associated with various autoimmune diseases . Today, Hashimoto is one of the most common acquired hypothyroidism and autoimmune disease in children and adults . The onset of autoimmune-thyroid disease with vitamin D deficiency is very common . Plenty of evidences have shown the role of vitamin D in the regulation of pro-inflammatory cytokines, regulatory T cell, and immune response . It seems that vitamin D deficiency leads to an increase in the risk of autoimmune diseases. Vitamin D also can reduce the pathogenesis of DCs cells, macrophage, CD4+T, CD8+T, and B cells . Besides, it has been shown as a selective immune inhibitor that plays an important role in suppressing and preventing the development of autoimmune diseases such as encephalopathy, rheumatoid arthritis, systemic lupus erythematosus, diabetes type 1, and intestinal inflammatory diseases [13-15]. Recent studies have shown the role of vitamin D deficiency in autoimmune thyroids, such as HT [16, 17].
To the best of our knowledge, there is contradictory research about the relationship between thyroid diseases, especially hypothyroidism and vitamin D deficiency; therefore, in the present study, we aimed at evaluating the vitamin D level in hypothyroidism patients. Besides, there was no study comparing the vitamin D level in immune and non-immune hypothyroidism, and the relationship between the anti tpo level and vitamin D, as well as the disease treatment status and vitamin D; hence, in the present study we evaluated the mentioned issues.
Study size and participants:
In the present case-control study, all hypothyroidism patients were selected among referents to the endocrinology clinic of Jahrom city in 2016-2017. In the study, the treatment group included patients with pre-diagnosed hypothyroidism under Levothyroxine therapy or newly diagnosed patients. Control group consisted of healthy people, who were similar with other group in terms of confounding variables. Exclusion criteria were to have collagen vascular and Celiac disease and type-1 diabetes mellitus. Finally 633 Immune Hypothyroid and 305 non-Immune Hypothyroid and 200 healthy subjects were enrolled (Figure1).
Normal thyroid function was considered as 0.3 mIU/L ≤ TSH ≤ 3.6 mIU/L. The diagnosis of overt and subclinical hyperthyroidism respectively were done based on TSH levels higher than 10 and 3.6 mIU/L <TSH ≤ 10 mIU/L . The values higher than 40 and 100 were considered positive for TPOAb and TGAb, respectively. Overt and subclinical hypothyroidism patients, whose one of TPOAb or TGAb antibodies was positive, were considered as HT patient.
Blood samples were taken from all participants after at least 8 hours of fasting. T3, Free T4, TSH were measured by Cobas ECLIAs (Roche Diagnostics GmbH, Mannheim, Germany). Thyroid peroxidase antibody (TPOAb) were determined by chemiluminiscenta IMMULITE 2000 XPi (Siemens, Eschborn, Germany). Thyroid globulin antibody (TGAb) levels were analyzed by Enzyme-Linked Immunosorbent Assay (ELISA kit, Diesel). Vitamin D levels were measured by LIAISON vitamin D chemiluminescence immunoassay (DiaSorin, Saluggia, Italy).
In order to compare the quantitative continuous variables, ANOVA for parametric data and Man-u withney and Kurskal wallis for non-parametric data were used. Chi-square test was used to compare discrete data among different groups. A p-value less than 0.05 was considered statistically significant. To statistical analysis, SPSS v.19 was used.
Demographic information and biochemical parameters of participants are presented in Table 1.
According to Table 1, in chi-square test and the right-tailed probability of the chi-square distribution, a significant relationship is observed between vitamin d deficiency and non-immune and immune HT (X 2 (2, N = 1138) = 29.77, p<0.001). However, there was no relationship between vitamin D deficiency and participating in the control group. Participants were divided into 4 groups (0-8 or severe vitamin D deficiency, 9-15 or moderate vitamin D deficiency, 16-20 mild vitamin D deficiency, >20 or vitamin D sufficiency) based on vitamin D level and the chi-square test was repeated. The results showed that in HT patient, vitamin D level of participants were more often in 8-15 ranges (X 2 (6, N = 1138) = 35.50, p<0.001). It means that mild vitamin D deficiency was observed in HT patient more than others. In other groups such as non-Hashimoto hypothyroidism and control group, the relationship was not significant (P>0.05)(Table1).
The relationship between thyroid autoimmune antibody and vitamin D:
A comparison was made between people with vitamin D deficiency and sufficient vitamin D (Table 2). The results of chi-square test showed that prevalence of HT among people with vitamin D deficiency is significantly higher than those with sufficient vitamin D level (X 2 (1, N = 1138) = 23/02, p<0.001). Besides, the positive TPOAb rate among people with vitamin D deficiency was significantly higher than those with sufficient vitamin D level (X 2 (1, N = 1138) = 14/85, p<0.01). However, there was no difference in terms of TGAb rate (X 2 (1, N = 1138) = 0/602, p=0/262).
Furthermore, in order to evaluate the severity of autoimmune disease in terms of one or two positive antibodies, the chi-square test was used for HT patients. In HT patients, we observed that in some cases only one antibody such as TPOAb or TGAB was positive and in others, both of them were positive. Those who had only one positive antibody had less severe autoimmune problems compare to those with two positive antibodies. The results showed that in HT patients, there was no difference in severity of autoimmune disease in terms of vitamin D deficiency (X 2 (2, N = 633) = 5/19, p=0/074).
In terms of vitamin D and by considering TSH level, among non-hashimoto patients who had a TSH level lower than 0.3, there were more number of vitamin D sufficient patients. But in other comparisons the contrary of this was true (Table3).
The relationship between vitamin D and the effectiveness of treatment
In the present study, the participants were evaluated in terms of thyroid gland function based on their statues after taking levothyroxine and then, their following program was determined for the coming months. In 203 patients, the necessity of reducing medicine dosage was observed due to the relative recovery. In 211 cases, the necessity of increasing medicine dosage was determined. In the rest of the patients, there was no need to change the dose. As shown in Figure. 2, the comparison between the level of vitamin D among the group in need of levothyroxine increase and decrease showed that women who needed their medication dose to be increased, had a lower serum level of vitamin D (P<0.001).
Sex difference in vitamin D level and hypothyroidism
Considering the higher level of vitamin D in men than women and the significance of this difference (P = 0.000), in Figure 3, the level of thyroid antibodies was compared by sex. TGAb level was significantly higher in women with vitamin D deficiency than in women with sufficient vitamin D level. However, there was no significant difference in TPOAb level between the groups of vitamin D deficiency and vitamin D sufficient by sex.
Hypothyroidism is a dysfunction in the central axis of the hypothalamus-pituitary-thyroid and insufficient secretion of the regulatory hormones is required by the thyroid gland . Hypothyroidism has various reasons that the most common causes are Hashimoto or autoimmune thyroid problems and iodine disorders . Previous studies have been explained pathophysiology involved in the role of vitamin D in preventing autoimmune thyroid disease. Vitamin D prevents aberrant immune responses by modulating the response of the immune cells . It seems that Vitamin D can affect thyroid function in other ways than modulating the immune system and preventing autoimmune diseases. However, a limited number of the study was performed in this field.
The results of the present research indicated that hypothyroidism patients with or without an immune base, deal with vitamin D deficiency (<20ng/mL) more than healthy people. Also, in patients with Hashimoto, mild vitamin D deficiency (vitamin D 15-8) was significantly reported more than other groups. In the study of Evliyaoğlu et al. , the patients with <20ng/mL vitamin D level was considered as vitamin D deficient and they showed that the prevalence of vitamin D deficiency is more common in people with Hashimoto than normal people. The results of the study were in agreement with those of the present study and other similar researches [16, 17, 23]. In the present study, a remarkable finding was the association between non-autoimmune hypothyroidism and vitamin D deficiency. It means that the vitamin D deficiency level in a patient with non-Hashimoto hypothyroidism was higher than the control group. The relationship between vitamin D deficiency and HT is well documented. The prevalence of positive TPOAb among people with <20ng/mL vitamin D level was more than people with sufficient vitamin D.
In the present study, the assumption that patients with two positive antibodies (TGAb and TPOAb) might have a severe condition in terms of vitamin D level was denied. Krysiak et al.  indicated that daily uptake of 2000 IU and vitamin D can improve the treatment process in women with HT. In our study, a comparison was made between the vitamin D level among people who needs an increase in Levothyroxine dosage and people who need a decrease in Levothyroxine dosage and the results showed that in women who needed an increase in Levothyroxine dosage, vitamin D serum level was low. It means that lower vitamin D leads to a decrease in response to treatment and a need for increasing the dosage of medicine.
Of course, the relationship between Hashimoto and vitamin D may also be affected by the patient’s condition. Some scholars believe that there are some differences in the past time since the onset of the disease. Effraimidis et al.  stated that there is no relationship between vitamin D level and primary stage of autoimmune thyroid disease. However, our subjects had crossed the initial stage of the disease. Age and sex differences may also be effective. In the present research, the male had a higher level of vitamin D than women. Additionally, TGAb levels were significantly higher in women with vitamin D deficiency than women in with sufficient vitamin D level. This means that in women, autoimmune factors may affect vitamin D more than men.
Colbay et al. showed the negative correlation between TSH and vitamin D level . Zhang et al.  indicated that the higher level of vitamin D leads to a reduction of circulated TSH, which are in agreement with the results of our study. The results of our study showed that among non-HT patients who their TSH level was reduced after Levothyroxine therapy, the number of people with sufficient vitamin D was higher than those with vitamin D deficiency (Table 3), while, it did not occur in HT patients. This finding suggests that in people with non-autoimmune hypothyroidism, treatment with levothyroxine in vitamin D sufficient individuals may result in more effective treatment and medication. Our study failed to justify the cause of this issue in non-hashimoto hypothyroid patients. Since the subjects of the present study were under Levothyroxine therapy, as an effective factor on TSH level, obtaining the results based on vitamin D level and finding the relationship between vitamin D and thyroid function was impossible. Barsony et al  demonstrated that the treatment of hypothyroidism with Levothyroxine led to an increase in vitamin D level. While Cayir et al. showed that long-term consumption of levothyroxine may disrupt the concentration of vitamin D . Therefore, there is a complicated relationship between them. Besides, similar clinical and laboratory studies did not address this issue, and they only showed the relationship between HT and vitamin D. Fournier et al. induced autoimmune thyroid disease on laboratory mice and showed the positive effect of vitamin D on suppressing of immune system and prevention of thyroid damage . However, the present study showed that vitamin D deficiency not only affects the immune system but also have a relationship with the function of the thyroid gland.
One of the strong points of the present study is the evaluation of vitamin D level in hypothyroidism patients who their disease wasn’t autoimmune. In the present study, TGAb and TPOAb antibodies were evaluated in thyroid patients, but other factors were not evaluated. Other strength points of our study were the role of vitamin D in the treatment of patients with levothyroxine. The stage difference of disease in participants was the limitation of the study. For future researches, we suggest matching factors such as the stage of the disease and the number of drugs received to evaluate the role of vitamin D deficiency in non-autoimmune thyroid disease.
The results of the present study showed that both autoimmune and non-autoimmune HT is associated with vitamin D deficiency. The relationship of vitamin D with non-autoimmune hypothyroidism is one of the new findings of the present research. In women with deficient vitamin D, TGAb level was significantly higher than women with sufficient vitamin D. Among non-HT patients that their TSH level was less than 0.3 after Levothyroxine therapy, the number of vitamin D-sufficient patients was significantly higher than vitamin D-deficient ones. This finding showed that in people with non-autoimmune hypothyroidism, treatment with levothyroxine in a patient with sufficient vitamin D can significantly be effective in treatment. Women with lower vitamin D levels also showed the higher need for increasing the dose of levothyroxine.
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We did not receive any grant from funding agencies.
Competing interests: None.
Ethics approval: The study was approved by the ethics committees of Jahrom University of medical sciences.
Contributors: The manuscript has been read and approved by all authors. All persons listed as authors have contributed to preparing the manuscript. SA designed the study and sample collecting was done by SA and MD. SA and NH undertook data analysis and writing the manuscript and reversions.
Data sharing statement: There isn’t any additional data but the data sets are available on internal medicine department of Jahrom University of medical sciences.
Table 1- basal characteristic
|Characteristic||Immune Hypothyroid||Non-Immune Hypothyroid||control
|Number, n (%)||633||305||200||–|
|Age، y (IQR)||37.48±13.18||36.65±14.56||37.69±15.26||0.630|
|SEX (maLE), n (%)||77(6.76)||37(3.2)||49(4.3)||0.001|
|levothyroxin , mg/kg/day (IQR)||400(0-700)||350(0-600)||0(0-0)||0.001|
|Vitamin D Deficient(<20 n/ml), n (%)||437(38.40)||186(16.34)||96(8.4)||0.001|
|Severe Vitamin D Deficient (0-8 n/ml), n (%)||133(21.01)||64(20.98)||33(16.5)|
|Moderate Vitamin D Deficient (9-15 n/ml), n (%)
|Mild Vitamin D Deficient (16-20 n/ml), n (%)||78(12.32)||32(10.49)||27(13.5)|
|TSH , mIu/l (IQR)||6.29(3.13-17.75)||5.92(2.54-1.81)||2.2(1.59-2.88)||0.001|
|T3, mg/ml (IQR)||1.67(1.26-2.38)||1.68(1.22-2.15)||1.32(0.74-1.8)||0.001|
|T4, mg/ml (IQR)||9.1(7.06-63.62)||11.1(7.42-80.05)||7.05(0.63-808)||0.001|
Table 2. Prevalence of positive antibodies.
|Characteristic||Vitamin d deficient||Vitamin d sufficient||P Value|
|Number, n (%)||719||419||–|
|TpoAb (positive) , n (%)||461||220||<0.001|
|TgAb (positive), n (%)||44||21||>0.05|
Table 3. Association of HT and vitamin D based on TSH levels.
|Vit D>20||Vit D<20||Vit D>20||Vit D<20||TSH level|
|93**||138**||57*||61*||Higher than 10|
*. Correlation is significant at the 0.05 level in each row of non-hashimoto patients.
**. Correlation is significant at the 0.05 level in each row of hashimoto patients.