The 20th century, especially the second half, ushered in one of humanity's greatest achievements: unprecedented improvements in life expectancy at birth for the world's population. Despite unfortunate setbacks due to HIV/AIDS, SARS and virulent influenza viruses, gains in life expectancy are continuing into the 21st century. We wonder: How many months of life expectancy at birth is the world’s population gaining annually?
A. One month
B. Three months
C. Five months
D. Seven months
A. One month is not correct.
While an increase in life expectancy at birth of one month per year is comparatively slow, many countries have not been able to achieve even this level of improvement. In addition to some sub-Saharan African nations that have been hard hit by the HIV/AIDS epidemic, nations such as Belarus, Russia and Ukraine have experienced actual declines in life expectancy following the collapse of the Soviet Union.
B. Three months is correct.
Today, the world's population is adding close to three months per year to life expectancy at birth, which currently stands at 69 years. The continuing improvements in life expectancy at birth, which are primarily the result of lower mortality at the higher ages in developed countries, are posing serious challenges for many national retirement and elderly healthcare programs.
C. Five months is not correct.
In Japan, which at 83 years has today's highest life expectancy at birth, average life expectancy increased by five months per year during the second half of the 20th century.
In comparison, the current gains in life expectancy for other developed regions, such as Europe and the United States, are considerably less, at three and two months per year, respectively.
D. Seven months is not correct.
A gain in life expectancy at birth of seven months per year is a very rapid pace. Nevertheless, the world's largest population, China, achieved an extraordinary gain in life expectancy of more than seven months per year during the 50-year period of 1950-2000. Starting at a low life expectancy at birth at mid-century of no more than 40 years, China ended the century with a life expectancy of 71 years.
Generally speaking, gains in life expectancy tend to be greater when countries are at low levels of life expectancy, as was the case in China during the 1950s and 1960s. After reaching a plateau of high life expectancies, as now attained in countries such as Japan, Switzerland, France, Italy and Sweden, achieving further large gains in life expectancy at birth becomes more difficult.