The one social factor that has been consistently linked to longer life, regardless of country, is education. It is far more important a factor than even health insurance.
A few extra years of school is associated with extra years of life, as well as vastly improved health during old age.
Not only have studies consistently shown this connection, but there is no limit beyond which more years of school stop adding to a person's life span. There are several theories as to why this may be the case, including a better ability to plan for the future.
Other factors that seem to greatly affect health include tight social networks of friends and relatives, and income level.