It’s one of the most enduring questions that we humans have been asking ourselves throughout the ages: What makes for a happy life? Some argue that it’s money; some, a fulfilling career; some point to the role of family and children. But while it’s fun to speculate and compare ideas, there is actually a body of science we can turn to to help us figure out some of the answers, and it centers around the longest-running in-depth study of happiness in history.

The Harvard Study of Adult Development is now in its 86th year, but it started life as two separate projects. In 1938, the Grant Study, funded by the William T. Grant Foundation and led by Dr George E. Vaillant, recruited 268 men from the undergraduate classes at Harvard University. In tandem, another study was being performed – the Glueck Study, with a cohort consisting of 456 men from the inner-city neighborhoods of Boston.

Both studies had similar aims: to follow their recruits over their lifetimes and observe how various factors would impact their health and happiness as they grew older.

Few of the original participants are alive today, but some went on to have illustrious careers – including legendary journalist Ben Bradlee and an actual US president, John F. Kennedy.

Latterly, the researchers have moved on to looking at the children of the original group – the Second Generation Study – under the leadership of psychiatrist Dr Robert Waldinger.

Together with associate director Dr Marc Schulz, Waldinger published a book called The Good Life: Lessons from the World’s Longest Scientific Study of Happiness, summarizing the findings from this decades-long undertaking. Dozens of scientific papers have been published over the years, studying the participants as they hit different life milestones and looking at factors ranging from military service to spiritual experiences.

So, what has the longest-ever study of human happiness taught us so far?

One is the loneliest number

“The surprising finding is that our relationships and how happy we are in our relationships has a powerful influence on our health,” Waldinger told The Harvard Gazette in 2017. “Taking care of your body is important, but tending to your relationships is a form of self-care too. That, I think, is the revelation.”

A wealth of research in recent years – not least during the socially distanced days of COVID-19 shutdowns – has pointed to the potential health risks associated with loneliness. Some studies have suggested that isolation could be as deleterious to health as smoking or obesity. Loneliness in elderly people has been linked to heart disease, while social connections have been associated with better brain health.

This particular lesson from the Harvard Study could arguably not have come at a better time. Many have warned about the “loneliness epidemic” that’s supposedly plaguing our modern world, with the World Health Organization arguing that the issue should be “recognised and resourced as a global public health priority.”

That’s not to say that the answer to happiness is to surround yourself with as many people as you possibly can at all times. As Waldinger expanded in an interview with science communicator and YouTuber Derek Muller on his channel Veritasium, not everyone needs huge numbers of social connections.

“Introverts are perfectly healthy,” Waldinger said. “They just may need one or two really solid relationships and don’t want a lot more people. Nothing wrong with that at all.”

This is less about quantity and more about quality. Being married has been linked to a decreased risk of dementia in later life, but if your marriage is an unhappy one, that’s likely to outweigh any benefit.  

A recent study suggested that while American adults today have a similar number of friends to their counterparts in previous decades, the quality of their social connections may not be quite the same, and those relationships may not be as fulfilling.

In our hyperconnected world, many have suggested that spending more of our time online and less of it out in the world could be a barrier to forming strong connections with others. This is unlikely to be the case for everyone – for example, for people who are unable to leave their homes, online friendships can be a vital lifeline – but it could form part of a complex picture.

As to why good relationships are so valuable, Waldinger suggested that the prevailing theory centers around our ability to emotionally regulate through social interaction. A stressful day at work is often relieved by being able to talk things through with your partner when you get home; and if you’re going through a tough time with your partner or kids, it might help to be able to vent to a close friend.

The importance of relationships is only one of the lessons from the study, but it might be the most unexpected. Other predictors of long-term wellbeing are things we’re very familiar with: abstaining from smoking, not drinking to excess or using drugs, exercising regularly, and getting regular health checks all help promote physical health, which has an important knock-on effect on happiness.

The Harvard Study is still ongoing, but as Waldinger once said in a TED Talk, there’s one inescapable conclusion: “the people who fared the best were the people who leaned into relationships.”