First off to better understand the role of social capital we must know what it means. Social capital can be defined as the resources that can be accessed by groups as well as individuals within a social structure which facilitate cooperation and action.
Next, "social network" in health can be defined as the social connections between people. These connections between people actually help people become informed about health thus resulting in better health of people in a community.
Health is actually affected by social capital and social networks. This is because your health can heavily depend who you're connected with (your "network" of people) so if you have a small or no network, you're at higher risk of contracting diseases and being less healthy.
Next stress plays a big role on your all around health. If someone is stressed they may not reach out to other people (their social network) and continue to become more ill. So people who are more stressed tend to have worse health than those who are not.
I have personally been affected by stress and not reaching out to my social network. Last year before my Chemistry final, I wasn't sleeping from stress and studying constantly. I started becoming sick and didn't tell anyone about it, until eventually I could barely breath. After the final exam, I went to the hospital and found out I had Pneumonia.
What I found most interesting about these readings was in fact that stress can cause you to become more ill. I never linked stress to a reason why I may have contracted pneumonia last year, but it all makes sense now!