Endocrine Abstracts

Background: vitamin D has been associated with different beneficial effects on the immune system. The vitamin D activating (CYP2R1 and CYP27B1) and inactivating (CYP24A1) enzymes, including the vitamin D receptor (VDR) are expressed in several types of white blood cells (WBC). A range of studies have explored whether vitamin D positively affects risk of and severity of respiratory tract infections such as tuberculosis, influenza, cold and COVID-19.

Objective: To determine the effect of high-dose vitamin D supplementation on WBC count, CRP and self-reported upper respiratory tract infections in infertile men.

Method: A single-center, double-blinded, randomized, placebo-controlled clinical trial (NCT01304927). Sample of 307 infertile men. The active group (n=151) initially received 300,000 IU cholecalciferol followed by 1400 IU + 500 mg calcium daily for 150 days, compared to the placebo group (n=156). The primary endpoint was to assess the effect on semen quality, which has previously been reported. The effects on WBCs (Leucocytes, neutrophile, basophile, eosinophile, lymphocytes and monocytes), CRP and self-reported symptoms of cold, influenza and fever were secondary endpoints.

Results: At baseline serum 25OHD₃ were negatively correlated with leucocyte (* r=-.207; P<0.001), neutrophil (* r=-.151; P=0.009), eosinophil (* r=-.158; P=0.007), lymphocyte (* r=-.191; P<0.001) and monocyte (* r=-.160; P=0.006) counts. Moreover, at baseline men with vitamin D insufficiency (serum 25OHD ≤ 50 nmol/l) had significant higher eosinophile, lymphocytes and monocytes compared to men with vitamin D sufficiency (serum 25OHD > 50 nmol/l) (0.22 x 10⁹/l vs. 0.19 x 10⁹/l; P=0.038, 2.1 x 10⁹/l vs. 2.0 x 10⁹/l; P=0.046 and 0.48 x 10⁹/l vs. 0.44 x 10⁹/l; P=0.024, respectively). After the vitamin D intervention there were no differences in WBC count, CRP or number self-reported upper respiratory tract infections (25% vs 20%, P=0.062) between men receiving vitamin D supplementation compared to men receiving placebo. Furthermore, a predefined subgroup analysis of men with vitamin D insufficiency (serum 25OHD ≤ 50 nmol/l), showed no difference in WBC count, CRP or self-reported respiratory infections between men receiving vitamin D supplementation compared to men receiving placebo. *r: Pearson correlations coefficient.

Conclusions: High-dose vitamin D supplementation did not alter WBCs, CRP or risk of upper respiratory tract infections. However, serum 25OHD₃ were negatively correlated with the majority of WBC, which indicates that 25hydroxylation of vitamin D may be linked with inflammation and WBC turnover.