When it comes to ‘SEX’, I think we forget that this is also just another need like feeding ourselves, stay socialize, etc. but unfortunately, we end up making it a taboo. We human beings inherently have this need since our inception; therefore, in my opinion, it can not be put into a certain parameter. However, having said that, I believe that you can relish this activity as long as you enjoy it. For some, it can be once in a blue moon while for many it is quite often and both types of couples are still happy in their own nest.
I don’t know you would be agreed or not, but I read HEALTH as both Physical and Psychological and the aforementioned explanation that I gave is largely associated with our psychology.
On the other hand, if we see it as healthy or unhealthy, it's very healthy until you and your partner love to put yourself into it. In addition, it’s been scientifically proven that sex helps you reduce weight, strengthen your heart, improve your relationship, and what not.
So in a nutshell, have sex no matter less or more. Simply, enjoy it! Quality sex is all we need, right?
Animals 
Beauty 
Careers 
Cinema 