Objective: Interrelationships between hormones of the hypothalamic-pituitary-testicular (HPT) axis, hypogonadism, vitamin D and seasonality remain poorly defined. We investigated whether HPT axis hormones and hypogonadism are associated with serum levels of 25-hydroxyvitamin D (25(OH)D) in men.
Design and methods: Cross-sectional survey of 3369 community-dwelling men aged 40-79 years in eight European centres. Testosterone (T), oestradiol (E(2)) and dihydrotestosterone were measured by gas chromatography-mass spectrometry; LH, FSH, sex hormone binding globulin (SHBG), 25(OH)D and parathyroid hormone by immunoassay. Free T was calculated from total T, SHBG and albumin. Gonadal status was categorised as eugonadal (normal T/LH), secondary (low T, low/normal LH), primary (low T, elevated LH) and compensated (normal T, elevated LH) hypogonadism. Associations of HPT axis hormones with 25(OH)D were examined using linear regression and hypogonadism with vitamin D using multinomial logistic regression.
Results: In univariate analyses, free T levels were lower (P=0.02) and E(2) and LH levels were higher (P<0.05) in men with vitamin D deficiency (25(OH)D <50 nmol/l). 25(OH)D was positively associated with total and free T and negatively with E(2) and LH in age- and centre-adjusted linear regressions. After adjusting for health and lifestyle factors, no significant associations were observed between 25(OH)D and individual hormones of the HPT axis. However, vitamin D deficiency was significantly associated with compensated (relative risk ratio (RRR)=1.52, P=0.03) and secondary hypogonadism (RRR=1.16, P=0.05). Seasonal variation was only observed for 25(OH)D (P<0.001).
Conclusions: Secondary and compensated hypogonadism were associated with vitamin D deficiency and the clinical significance of this relationship warrants further investigation.