For example, sex can actually cause you to get fewer colds. Research has shown that couples who have sex weekly have a 30 percent increase in immunoglobulin A, an antibody that fights infection. Sex can also help women have a more predictable period schedule, as a result of being exposed to male pheromones.
In addition, having sex reduces stress — for physiological as well as emotional reasons. Sex activates a nerve that has a calming effect. Having sex also lowers blood pressure, which reduces the risk of heart disease.
Sources: ABC News June 16, 2009