Fig. 1

Regional differences in semen quality and in testicular cancer rates. Median sperm concentrations of young men (adjusted for a period of sexual abstinence of 96 h) are indicated in a color gradient, with the darkest green corresponding to the group of countries with the highest sperm concentration. Testicular cancer incidence rates (age-standardized World per 100′000) in Europe and Japan are also shown with different patterns. Red dots indicate the cities where the studies were performed and the circle around Switzerland refers to the whole country. The map was adapted from [50] and the sources of data on sperm concentration were extracted from [51,52,53,54,55, 56] and as personal communications from J. Axelsson and J. Erenpreiss. Cancer data were obtained from [57]. A correlation between sperm concentration and the incidence of testicular cancer in Europe was observed using a Spearman Rank Order Correlation (r = 0.74, P = 0.01). Mio/mL: Million/milliliter