Endocrine Abstracts

Vitamin D has a role in the pathogenesis of thyroid autoimmunity.

There is evidence in humans that serum levels of 1,25(OH) D3 were found to be significantly lower in patients with autoimmune thyroid diseases.

We have evaluated all samples performed in the endocrine labs tested for vitamin D, AbTg, Ab-TPO and TSH from 2006 to 2015; 29216 samples for vitamin D and 41014 for TSH, AbTg and TPO were considered.

We studied if the seasonal variations of vitamin D, that peaks in summer and has a nadir in winter, could influence levels of TAb and TSH.

Vitamin D levels in summer were significantly higher than in other seasons. Vitamin D from a mean level of 19 ng/ml in winter raises significantly in spring reaching an average level of 26 ng/ml in summer and descending in autumn reaching nadir in winter.

About TSH and thyroid antibodies, in particular AbTg shows an opposite trend compared to Vitamin D. AbTg has a peak in winter around 7 ng/dl descending to 6 ng/dl in spring and remaining of similar value during the rest of the year. Interestingly TSH has a small but direct correlation with the AbTg variation ranging within normal values but following a similar trend of that of the antibodies (Pearson correlation r=0.009, P=0.03).

In conclusion our results seem to confirm an immunodepressive role of vitamin D on thyroid autoimmunity; in summer when the maximum level of vitamin D was reached, the concentration of TgAb was at minimum, while in winter at the lowest level of vitamin D the TgAb titer reached their peak.

Respectively TSH follows the trend of AbT, when AbT level decreases in summer at the maximum of vitamin D, thyroid function expressed by TSH ameliorates, while in winter at the maximum of AbT TSH is higher, corresponding to the lowest level of vitamin D.