My dad's neglecting his health

I'm worried sick about my dad. He's been ignoring his health lately. Ever since the divorce, since last year, he's been living alone, and I think it's taking a toll on him. I've visited him 5 times this fall and each time he looks less and less like his old self. What scares me the most is that he's skipping his doctor's appointments. He has high blood pressure, but he says he "feels fine" and doesn't need to go. I'm afraid something bad might happen if he keeps this up. I've tried talking to him about it, but he just brushes me off. He says I worry too much and that he's "old enough to take care of himself." But I can see he's not doing a good job of it. Mom's worried too, even though they're not together anymore. She's asked me to keep an eye on him, but I feel so helpless. I'm the only child and I feel like it's my job to make sure my folks are okay