It's great that you have niche blog and I think you can earn much more by affiliate marketing. I'm also doing same. (Using minimum Ads on my niche website)
Now come to your question, There is no limit to earn on Health blog too. It depends on How much your visitors trust on you, Is it targeted traffic and what are your strategies to promote affiliate products.
Most Important- never be greedy by posting too much affiliate links or Ads in one post.