Sex is a natural part of life, and a number of studies have pointed to specific health benefits from regular sex -- including a stronger immune system and lower blood pressure. This quick Anyhoo video runs down the benefits.
From lower blood pressure to lower risk of heart disease (in men) to higher antibody counts in the bloodstream (an indicator of a stronger immune system) to the calories burned during regular sexual activity, there are lots of physical reasons to not just have sex more often, but do it regularly.
Even though it was a small exercise (and obviously could have been influenced by outside factors), a panel of judges at a hopital in Scotland tried to guess people's ages based on appearances alone, and lo and behold, the people who had sex an average of four times a week were perceived to be 7-12 years younger than their age. That's definitely not a study you'll see in a peer-reviewed journal, but I'm making the call on this one: If all you need to do to even possibly look younger, feel younger, and be more healthy is have sex more often, then by all means, get it on.
6 Surprising Ways Sex Is Good For You [Anyhoo (Youtube)]