Beginning in 1938, researchers at Harvard began tracking 268 male undergraduates over their entire adult lives in one of the longest-running studies of human development ever conducted — the Harvard Study of Adult Development (Grant Study).

The Core Question

What factors predict a long, healthy, happy life?

The Key Finding

After 75+ years of tracking, the study's director George Vaillant summarized the single most powerful predictor of late-life flourishing: warm relationships.

The men who were most satisfied in their relationships at 50 were the healthiest at 80. The quality of close relationships in midlife predicted physical health, mental health, and longevity more powerfully than income, social class, IQ, genetics, or any other measured variable.

What Didn't Predict Well

• Cholesterol levels at 50 predicted physical health less than relationship satisfaction
• Early signs of alcoholism (not the alcoholism itself, but its trajectory) were the single strongest predictor of mental and physical decline

The Bottom Line

Loneliness is as damaging to health as smoking 15 cigarettes a day. Connection is the most powerful medicine available — and the most systematically undervalued.

Reference:

Wikipedia: Harvard Study of Adult Development

https://en.wikipedia.org/wiki/Harvard_Study_of_Adult_Development