Volunteer. There are tons of ways to help out in your community through direct action. Ask at your local religious organization, or non-profit. Check out programs at your local library and see if they need assistance.
There are many different groups that you can work with: children, the elderly, the mentally ill, the homeless, women. You'll need to decide which group you want to focus on.
You can do things like teach a course in resume development, computer skills. You could start up a local community garden and teach courses on how to grow sustainable food. A large number of people who are poor cannot afford to buy much produce, so teaching them a sustainable and cheap way to grow their own food, could help alleviate some of that vitamin deficiency.
You can work in shelters, soup kitchens, community centers, at after-school programs, and employment centers.