Vegans who are vegans for health reasons - dumb dumb dumb. A cursory biological examination of the human body demonstrates that we are omnivores. That means the human body has adapted over tens of millions of years to eat both plants and animals.
Additionally, many vegans will go heavy on soy and wheat based foods. There are many health issues surrounding soy (citations my other comment in this thread), and wheat products are not particularly healthy.
The arguments for veganism for health reasons is largely unsupported by any sort of actual science.