The best part of Cattail is that it is a purifier of the water. Whatever is in the water the Cattail will absorb and clean the water within a few short months. That is why it is important that you know the source of the water as a Cattail will absorb any toxins in the water and then you will consume it. 

All in all this is a great plant to forage for or to grow for food,medicine, and home use. It always shows up on the top 10 plants to use in America.

I searched the NIH database and could find no studies regarding Cattails. However some independent research is showing promise for the internal use of cattails for stopping the growth and spread of cancers. The research is being done in China and no results have been published yet.