Of the 56.4 million deaths worldwide in 2015, more than a quarter were down to just two diseases: heart disease and stroke.

These two conditions have remained the world's biggest killers in the last 15 years, accounting for a combined 15 million deaths in 2015, according to data from the World Health Organisation (WHO).

Aging populations around the world have led to a surge of new diseases that plague humans alongside these, such as diabetes and dementia.

Diabetes killed 1.6 million people in 2015, up from less than one million in 2000, while dementia-caused deaths more than doubled between 2000 and 2015. Both of these killed more than road injuries.