Complex sentence: Ageing is among the largest known risk factors for most human diseases: roughly 100,000 people worldwide die each day of age-related causes, and it is the major cause of mortality in the developed world.
Split into simpler sentences: Ageing is among the largest known risk factors for most human diseases. Roughly 100,000 people worldwide die each day of age-related causes, and is the major cause of mortality in the developed world.