Health is certainly as much a social issue as it is a medical one. This is because so many of the medical issues stem from social issues.
For example, a major problem in many poorer communities is access to (and time to make) nutritious meals. The lack of quality grocery stores in poor neighborhoods is a social issue, not a medical one. So is the fact that many poorer families lack the time to prepare meals from scratch (which tend to be healthier).
As another example, some unhealthy behaviors are tied to social traditions and values. I recently saw an article in the NY Times about Asian immigrants still tend to smoke a lot because that is how they grew up. I have seen articles about African American churches in the South trying to help break congregants' habit of eating lots of fried and fatty foods. These are social issues, not health issues.
Society and our culture affects many of the things that we do that influence our health. Therefore, health is a social issue, not just a medical one.