The four reasons for increased life expectancy is caused by better healthcare, better nutrition, better sanitation , and better working conditions. The United States has a really good healthcare system, but could be pricey. The United States has A LOT of food, you can see restaurants, fast food, and supermarkets everywhere, people in the U.S have easy access to food. The U.S is also cleaner than other countries, good water and sewer systems make sanitation good. Finally, the U.S has a lot of job opportunities for people to work.