This is a really broad question. I am not sure where you are in life or what your life experiences have been. There has been a lot of research of various degrees of validity. That is the great thing about medicine and science it is always changing. Just remember a false proof is just as important as a positive one when doing research. Research is difficult to be unbiased as most of the funding comes from someone looking to prove or disprove something. When looking at a study consider who funded it. Second look at how the study was done and look for bias and the quality of the study.