I think you may be referring to the Roseto effect. https://en.wikipedia.org/wiki/Roseto_effect
This community had unusually low rates of heart disease despite a large range of traditional risk factors. The general consensus was that this was due to the community-oriented nature of the town. Later they did follow-ups and found that as the town became more stereotypically "American" the mortality rates due to heart disease increased, especially among younger men.