Why has life expectancy increase?

Answer 1

The very large increase in average life expectancy in the 20th century is due to four major factors, and two minor ones. These factors are (from most important to least):

1. Clean drinking water
2. Universal sewage and high levels of personal hygiene
3. Better nutrition, particularly at the pre-natal, infant, and childhood levels
4. Vaccination against most epidemic diseases
5. Higher access to lifesaving trauma care
6. Improved drugs

#1 and #2 are by far the biggest contributors to increased life expectancy. Besides vaccines, about the only drugs that has made a major contribution to life expectancy are antibiotics.

Answer 2

The two biggest reasons - in developed countries - are better nutrition and better medical care.