Complex sentence: Numerous claims have been made for the health benefits of green tea based on chemical composition, "in vitro", and animal studies, and while preliminary research on many of these claims is promising, many also require further study to evaluate.
Split into simpler sentences: Numerous claims have been made for the health benefits of green tea based on its chemical composition, "in vitro studies", and animal studies. Preliminary research on many of these claims is promising, but many also require further study to evaluate.