For 75 years Harvard University has been tracking two groups: 456 poor men from Boston and 268 Harvard graduates - very much the haves and the have-nots.
Its conclusion from tracking their lives over three-quarters of a century is that the key to keeping us happier and healthier is good relationships.
In other words, love keeps us happy.
Researchers discovered that when you have someone to rely on, your nervous system relaxes, your brain stays healthier for longer and reduces both emotional and physical pain. You don't just feel better - you are better.
So finding the right one is the key to it all.
But the question that plagues so many of us - the question that has launched legions of reality TV shows: how do you know when you've found the one?
Divorce statistics suggest it can take a few goes to get it completely right. In 2015 marriages and civil unions totalled 19,947, but divorces totalled 8,463 - that's 42 percent of the number of unions.
It doesn't deter us though. Even though marriage is dipping off, de facto relationships are on the rise. Maybe we instinctively realise what it took the Harvard researchers 75 years to conclude - that relationships keep us healthy.