If we want a long, disease-free life, then we need to do more than just perfect our own diets and yoga schedules. We need to attend to the health of everyone in our communities. An increasing amount of research shows that good health practices and outcomes can spread throughout a community, even outweighing the influence of immediate family members.

Tracy Matsue Loeffelholz is the former creative director at YES!, where she directed artistic and visual components of YES! Magazine, and drove branding across the organization for nearly 15 years. She...