Friendships have a huge impact on your mental health and happiness. Good friends relieve stress, provide comfort and joy, and prevent loneliness and isolation. Developing close friendships can also have a powerful impact on your physical health. Lack of social connection may pose as much of a risk as smoking, drinking too much, or leading a sedentary lifestyle. Friends are even tied to longevity. One Swedish study found that, along with physical activity, maintaining a rich network of friends can add significant years to your life.