Are there any negative side effects to masturbating once or more a day?

Absolutely not, masturbate away!

You really can’t masturbate too much unless it starts to interfere with other responsibilities. It can be unhealthy if you start choosing masturbation over seeing your friends, family, going to work, leaving the house, bathing… It’s also a good idea to stop masturbating if you start rubbing yourself raw and begin to hurt.

Aside from the extreme side of the spectrum, masturbation is a healthy part of your sexual buffet. Enjoy with gusto.