Latest study by the UN's World Health Organization (WHO), life expectancy in the world's poorest countries increased an average of nine years in the last two decades.

Based on its 2014 statistics, six countries managed to increase life expectancy from 1990 to 2012. The top country was Liberia which average lifespan increased 20 years from age 42 to 62. Ethiopia comes second from age 45 to 64 then come Maldives from 58 years old to 77, Cambodia from 54 years old to 72, East Timor from 50 years old to 60 and Rwanda from 48 years old to 65.

The U.S. has a life expectancy of age 81 for females and 76 for males but only ranks 37^th, not making the top 10 countries for both genders. Japan has the highest life expectancy for females at 87 years while Iceland has the highest for males at 81.2 years.

An average girl who was born in 2012 can expect to live until 73 while an average boy's life expectancy is 68. It gives people born in 2012 six years more life expectancy than those who were born in 1990. Overall, the global average life expectancy increased six years from 1990 to 2012.

"An important reason why global life expectancy has improved so much is that fewer children are dying before their fifth birthday," chief Margaret Chan of WHO said. She added that there is a major divide between the rich and poor with rich countries having a better chance of longer life than people in poor countries. 

Years of lost life due to the largest causes of early deaths in year 2000 such as respiratory infections and diarrhea fell by 30 percent and 40 percent respectively in 2012, a time when ischaemic heart disease became the largest early death cause. Years of lost life due to road injuries increased 14 percent during the same period.

High-income countries gained much life expectancy because of the success in addressing noncommunicable diseases. Less people now die before age 60 due to a stroke or heart disease. Richer countries are now better at managing and monitoring diseases. Another key factor in longer lives for some countries is the declining use of tobacco.