A recent study in the Journal of Human Reproduction, June 2012, showed that wearing tight fitting underwear is associated with a lower motile sperm concentration - A. C. Povey et al. This study also showed no correlation between sperm quality and obesity, smoking, or drinking, which is an unfortunate message to give dad's to be, as there is absolutely no doubt that the health of the father plays a role in the health of the off-spring, long term.