A report from BYU and UNC found that people with no poor social connections experience a major effect in their life expectancy.
The difference in life expectancy between having strong or poor social connections is roughly the same as smoking 15 cigarettes a day.
What's worse, the effect is greater than obesity and physical inactivity.
Another study done by Carnegie Mellon found that people with more social connections and a diverse social network were LESS likely to develop a cold than people with less connections.
If you want some tips on strenthening your current relationships, check the source.