Complex sentence: Dehydration and overhydration are known to influence people's tendency to be a night owl or a lark, with those that are a lark tending towards dehydration and those that are night owls tending towards overhydration.
Split into simpler sentences: Dehydration and overhydration are known to influence people's tendency to be a night owl or a lark. With those that are a lark tending towards dehydration and those that are night owls tending towards overhydration.