I'm always a sucker for those $0.99 e-books on Amazon. I'll buy anything for a dollar, and my amazon kindle gets more money out of me then I ever thought possible.
Other than that, I would think anti-aging is a good buzzword that would pull in more potential readers of your e-book.
I would personally read an e-book that helped me to understand how to replace NSAID's with natural alternatives, and there's a lot of crossover between natural anti-inflammatories and antioxidants.
I read an incredible book recently that changed my life:
https://www.amazon.com/Forbidden-Heal.../dp/1928782248
Anyways I now use vitamin C powder every day, and my understanding of antioxidants is now much greater than it was. I now view Vitamin C and other antioxidants as natures "Electron Currency".
I hope I've been helpful, I really wish you luck and hope you succeed.
All the best!