In the 10 years after South Africa became a democracy in 1994 they managed to reduce their average life expectance from 61 to 51.
I don't think that a country can do much worse than South Africa as it became a democracy.
Yeah, South Africa was led by an HIV denialist for a decade. Despite Jacob Zuma's many other flaws, he has been a huge improvement in this regard . He massively expanded the distribution of ARVs, and the country's life expectancy is now back up to 60.
As Multiheaded added, "Personal is Political" stuff like gender relations, etc also may belong here.