Some niches harder than others for SEO?

HI everyone I am fairly new to this forum but not that new to SEO.So I know how to do good keyword research, SEO a site for the search engines and back linking down pretty good.

I have been fairly successful at gettting traffic naturally from the search engines in the past however I am now trying to launch sites in the health niche. Targeting low competition search terms. that all have less then 100,000 pages when searched for in quotes in Google and have very low strength of competition within the first 3 pages of Google in other words I look for Youtube.com Ezine Articles, article base stuff like that. However I am not seeing the results that I normally do. This is quite frustrating and was wondering If I could get some advice from more Experienced SEO experts.

I have a couple of questions number one is the Health niche incredibly hard to break into the top ten of Google? Does Google not allow/trust new sites that are health related?

Does it generally take longer for Health sites to rank? and if so how long and how can I shorten the process

Also are there SEO marketers in here who have had success with launching Sites in the health niche? and can some of you share some feedback as to how and what exactly yo you did differently then other niches in order to break into the top ten of Google.

Can someone please offer some guidance and share some of there experiences what works what doesn't work.

thanks in advance

Heat