Case Study: Does Molybdenum Decrease Testosterone?

This chapter applies Bayesian network (BN) learning methods and other techniques from Chap. 9 to the following health risk question: Does exposure to the metal molybdenum (Mo), as indicated by Mo concentrations in urine, reduce total testosterone (T) concentrations in blood serum of men, posing a potential risk to male fertility? Some recent papers have suggested that it might. For example, Lewis and Meeker (2015) state that “In adjusted analyses where metals were modeled as a continuous variable, we found significant inverse associations between urinary molybdenum and serum copper and serum testosterone. …These findings add to the limited human evidence that exposure to molybdenum and other metals is associated with altered testosterone in men, which may have important implications for male health” (Lewis and Meeker 2015). The adjusted analyses referred to consist of multiple linear regression models of data for 484 men aged 18–55 years old with data on Mo and other metals, serum T, body mass index (BMI), poverty income ratio (PIR), race, serum cotinine, and urinary creatinine who were enrolled in the National Health and Nutrition Examination Survey (NHANES 2011–2012). Similarly, Wang et al. (2016) concluded that, among men attending an infertility clinic, environmental exposure to tin, nickel, zinc and molybdenum may be associated with decreased total testosterone, although further prospective research is needed to confirm these associations in the general population. Conversely, however, some animal studies suggest that Mo exposure may actually improve male fertility. For example, Liu et al. (2019) found that Mo could repair sterility in male mice under experimental conditions, and proposed that it might be a new candidate medicine for treatment of male infertility. For humans, Rotter et al. (2016) found positive correlations between Mo and T. Finally, some investigators have found no relation between Mo and T. For example, using multiple linear regression, Zeng et al. (2013) found significant negative associations between urinary Mn and Zn and serum levels of T among men attending an infertility clinic, but no relationship between urinary Mo and T. Thus, the literature appears to be mixed and inconclusive on whether Mo is associated with reduced (or increased or unchanged) levels of T in serum in multiple regression models.