The increase in average life span in the 20th century is credited to public health achievements , such as vaccination programs and control of infectious diseases , effective safety policies of motor-vehicle and occupational safety , improved family planning , chlorination of drinking water , smoke-free measures , and programs on decreasing chronic disease such as cancer , heart disease and more physical exercise . During the 20th century , the dramatic increase in average life span is widely credited to public health achievements , such as vaccination programs and control of infectious diseases , effective safety policies such as motor-vehicle and occupational safety , improved family planning , chlorination of drinking water , smoke-free measures , and programs designed to decrease chronic disease .