Research

  1. The lower temperature in the scrotum is a prerequisite for normal spermatogenesis.

<Oxford Textbook of Medicine> by David A. Warrell, Timothy M. Cox, John D. Firth.page. 282, (line 32). Published by Oxford University.

  1. Heat can reduce sperm count and testosterone production.

University of Wisconsin Integrative Medicine

  1. According to this study from Nakamura et al. Human testis perform at their best when they’re around 31-36 °C (87-96 °F). anything hotter than that will negatively impact DNA synthesis, spermatogenesis, and most likely also testosterone production.

http://www.anabolicmen.com/cold-showers-testosterone/

  1. A low testosterone [hypogonadism or testosterone deficiency syndrome (TDS)] may be present in 30% of men and present in a number of different ways.

There is increasing evidence that TDS is associated with all-cause mortality and in particular cardiovascular death

European Heart Journal (OXFORD Academic)

http://eurheartj.oxfordjournals.org/content/31/12/1436

  1. Low levels of testosterone in men could increase their risk of developing diabetes.

The University of Edinburgh

http://www.ed.ac.uk/news/all-news/diabetes-040305

  1. Low Testosterone Associated With Obesity and the Metabolic Syndrome Contributes to Sexual Dysfunction and Cardiovascular Disease Risk in Men With Type 2 Diabetes

American Diabetes Association 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3120209/

  1. Male Obesity Linked to Low Testosterone Levels

University of Buffalo

http://www.buffalo.edu/news/releases/2010/05/11311.html