Low total testosterone (TT) is present in about 30% of men aged >60 years and in up to 7% of younger men. Male hypogonadism is associated with metabolic and cardiovascular diseases as well as with increased mortality. There is evidence showing a relationship of TT with vitamin D in men. We aim at evaluating the effect of vitamin D supplementation on TT and metabolic parameters in hypogonadal men. We will study the effects of 20,000 IU vitamin D weekly in a 12 wk randomized, double-blind, placebo-controlled trial in 100 men with TT <3.0 ng/ml and 25-hydroxyvitamin D (25(OH)D) <30 ng/ml (patients) as well as in 100 men with TT ≥3.0 ng/ml and 25(OH)D <30 ng/ml (controls). Vitamin D supplementation might be a safe therapeutic approach improving TT levels as well as metabolic parameters in hypogonadal men. Further the effects of vitamin D on androgens will be evaluated in eugonadal men.

Hypogonadal men:

Inclusion Criteria:

• TT levels below 3.0 ng/ml (measured at the baseline visit and confirmed at study visit 1)
• 25(OH)D levels below 30 ng/ml (measured at the baseline visit)
• Male, age of ≥ 18 and <70 years
• Written informed consent before entered into study

Exclusion Criteria:

• - Hypercalcemia defined as a serum calcium > 2,7 mmol/L
• Oral or transdermal testosterone supplementation in the last 2 months before entering the study
• IM testosterone supplementation 6 months before entering the study
• Regular intake of vitamin D supplements before study entry
• Men with chronic diseases (such as diabetes mellitus, thyroid disease, endocrine disturbances in need of treatment (except hypogonadism), or diseases known to interfere with vitamin D intake or very sensitive to vitamin D intake (such as inflammatory disease with granuloma: sarcoidoses, tuberculosis, Mb Wegener, vasculitis, inflammatory bowel disease
• Intake of medication influencing metabolic or endocrine parameters (insulin sensitizers, insulin, glucocorticoids,…) in the last 3 months before study entry
• PSA >4 ng/ml (or >3 ng/ml in men at high risk for prostate cancer) (see state of the art)
• Palpable prostate nodule or induration
• Hematocrit >50%
• Untreated severe obstructive sleep apnea
• Severe lower urinary tract symptoms
• Uncontrolled or poorly controlled heart failure
• A history of prostate cancer, breast cancer, orchidectomy, chromosomal disorders (e.g. Klinefelter Syndrome)

Eugonadal men:

Inclusion Criteria:

• TT levels ≥3.0 ng/ml (measured at the baseline visit and confirmed at study visit 1)
• 25(OH)D levels below 30 ng/ml (measured at the baseline visit)
• Male, age of ≥ 18 and <70 years
• Written informed consent before entered into study

Exclusion Criteria:

• Hypercalcemia defined as a serum calcium > 2,7 mmol/L
• Oral or transdermal testosterone supplementation in the last 2 months before entering the study
• IM testosterone supplementation 6 months before entering the study
• Regular intake of vitamin D supplements before study entry
• Men with chronic diseases (such as diabetes mellitus, endocrine disturbances in need of treatment (except hypogonadism), or diseases known to interfere with vitamin D intake or very sensitive to vitamin D intake (such as inflammatory disease with granuloma: sarcoidoses, tuberculosis, Mb Wegener, vasculitis, inflammatory bowel disease
• Intake of medication influencing metabolic or endocrine parameters (insulin sensitizers, insulin, glucocorticoids,…) in the last 3 months before study entry
• PSA >4 ng/ml (or >3 ng/ml in men at high risk for prostate cancer) (see state of the art)
• Palpable prostate nodule or induration
• Hematocrit >50%
• Untreated severe obstructive sleep apnea
• Severe lower urinary tract symptoms
• Uncontrolled or poorly controlled heart failure
• A history of prostate cancer, breast cancer, orchidectomy, chromosomal disorders (e.g. Klinefelter)