Unfortunately, he may kill himself through this faster than he would otherwise. Vitamins are practically useless for healthy people if they have a good diet and exercise regime. Antioxidants are good in small amounts, but taking 3x or more of the recommended allowance has been proven over and over again, huge quantities of the population, to actually protect cancer cells against your own defences and cause higher cancer rates. That and a lot of pills don't have the best manufacturing process.
Be careful what pills you take.