Healththeory.com has 5 results in google, and those are from expiring domain lists. "Health Theory" has about 69,000 results, however, only four of the first ten results use the two words in context; the other six simply have the words in proximity (ie. "The demand for health: theory and applications"). Overture appears to be zero. The domain is okay, but without development, reseller value is very low --> reg fee to twice reg fee without development. Best way to get a yield will be to develop, garner traffic, and document those results. Good luck with your domain.