Everyone says he'll sleep better once he starts solids. Is there anything behind that?

Five months, waking twice a night. Every relative has the same line: start rice cereal now and he'll sleep through. Our doctor said around six months for solids and didn't mention sleep at all. I'm not starting early on a family theory. But I'd like to hear whether anyone saw a real change in sleep after solids, or whether it's one of those things people repeat because it happened to line up once.