• Harvard Study of Adult Development is among longest-running adult life studies
• Study tracked the lives of 724 Boston men for 80 years from 1938 and their kids
• Comes after researchers from Harvard ranked four leading diets based

Good relationships are more important than money and success for happiness, a new book based on the longest-running study of human happiness has shown.

The Good Life is based on the Harvard Study of Adult Development, which is among the longest-running adult life studies ever conducted.

The study tracked the lives of 724 Boston men for 80 years from 1938 and then went on to study their Baby Boomer children.

Robert J Waldinger, the psychiatrist and Zen priest who oversees the study, told DailyMail.com: 'The biggest surprising takeaway is that good relationships don't just make us happy as we go through life, but they keep our bodies and brains healthier and we live longer.’

The book is based on interviews that gauge ‘life satisfaction’ regularly through people’s lives - and turn many of our assumptions about what leads to happiness on their heads.

Waldinger’s TED talk, ‘What makes a good life? Lessons from the longest study on happiness’ has been watched 44 million times.

He says that the book - which came out in January - ‘takes a deep dive into the way relationships support our wellbeing’.

Below are some of the lessons about happiness in The Good Life:

Having friends makes you live longer

Social connection is strongly linked to health and a long life, the researchers say.

They point to a 2010 study that showed that people with strong social connections had a 50 percent greater chance of surviving any given year.