Male infertility is responsible for about 50% of the fertility problems that couples face. Infertility in males is often the result of reduced sperm court, abnormal sperm quality (e.g., reduced motility and altered morphology), or altered levels of sex hormones (e.g., reduced testosterone). A review of over 100 studies of sperm density from 1938 to 1996  found that human sperm count has significantly declined in North America and Europe since the 1940s. (Swan 2000) While the causes of this decline are not entirely known, fluoride exposure — particularly from high-concentration topical fluoride gels — must be considered as one of the potential contributing factors.

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