Lucianne.com links to a BBC article on the risks associated with a vegan diet. Their conclusion, following a longish summary of research findings, is that vegans need supplements as meat-free diets lack certain essentials for brain health.
I liked the info that vitamin B-12 is associated with better brain function in older folks. And sublingual B-12 tablets that dissolve under your tongue taste good too.
The main vegan drawback from my perspective is dietary boredom. I’m a happy omnivore who rarely eats a supper w/o meat. At other meals I consider meat a nice option, my favorite bacon cheeseburger is not an everyday item.