It's hard when you see soemone doing something that's totally inappropriate with their health. It sounds to me ( and I amy be worng) that he might be experiencing some anger and frustration about his "one life". I say this because in college, my husband went through a bit of that and started drinking and smoking and generally doing stupid things.
We were just starting to go out at the time, but I sat him down and we talkled about all the things he was doing, and how I loved him, and how much it worried me that he was unintentionally shortening whatever time we had together. It took time and collaboration, but he stopped smoking and brought the partying down to a dull roar lol.
Just be honest and patient with your brother. Tell him how much he means to you. And hope for the best.