i'd agree with DW. i got 2 letters from public health profs -- one from a biostats prof and one from a physiology prof. the physiology is for sure a science letter. the biostats is too (if math is considered a science -- is it?). the same thing would be true for some epi course profs. i don't think international health, health policy, etc.. would be considered science. some environmental health classes might be depending on the nature of the course.