 Data analysis and quality The primary end points for this protocol will be changes in sperm production evaluated by total sperm number, sperm concentration followed by number of progressive and motile sperm, morphologically normal sperm, sperm motility, progressive motility and morfology which will be compared by paired t-test. Multiple secondary endpoints exist but for the initial investigation focus will be on changes of the following secondary endpoints: Sperm DFI, FSH, Inhibin B, serum OPG, RANKL, OPG, vitamin D and calcium homeostasis. Subjects who terminate participation after visit day 1 but before visit day 180 will be included for data analysis up to the last day they provided semen and bloodsample. Men that only deliver semen samples occasionally or have missing data at any visit will still be included in the analysis. Men that do not meet the criteria in the protocol will be excluded from the analysis. Men with fever above 38.5 degrees Celsius will not be included in the analyses up to 3 months after the fever episode. Semen samples obtained with an abstinence period less than 24 hours or with a semen volume 1.5 ml will not be included in the analyses. Those values will then be carried forward for analyses. A significance level of 5 is used. For the primary analyses Bonferronu-Holm p-value correction is calculated additionally. For the secondary analysis no multiple test correction are used. Instead results are discussed in view of the multiple testing situations. 