When Jonathan Rauch fell into the doldrums in his 40s, he had no idea why. Life was good: he had a successful career, a solid relationship, good health and sound finances. Then he learnt about the happiness curve and it all became clear. Academics have found increasing evidence that happiness through adulthood is U-shaped – life satisfaction falls in our 20s and 30s, then hits a trough in our late 40s before increasing until our 80s.

Forget the saying that life begins at 40 – it’s 50 we should be looking towards.

Rauch, a senior fellow at the US thinktank the Brookings Institution, was so relieved to have found an explanation for the gloom that hit him and, he believed, many others in middle age that he became evangelical about spreading the word. He has written a book, The Happiness Curve: Why Life Gets Better After 50, which includes personal stories, the latest data and illuminating interviews with economists, psychologists and neuroscientists.

‘The most surprising thing is that age tends to work in favour of happiness, other things being equal,’ he says. ‘The most strange thing is that midlife slump is often about nothing.’

Hold off on splashing out on that flashy sports car or getting that tattoo though. It is not the same as a midlife crisis, which according to the stereotype demands an urgent, rash response. The slump isn’t caused by anything, according to Rauch. It is a natural transition, simply due to the passing of time.

‘It’s a self-eating spiral of discontent,’ he says. ‘It’s not because there’s something wrong with your life, or your marriage, or your mind, or your mental health.’

Not everyone will experience a sunnier outlook in their 50s and beyond, Rauch acknowledges, because factors such as divorce, unemployment or illness can counter this. But, other things being equal, the U-curve holds.

Rauch, an author and journalist, adds: ‘Those most likely to notice the arrow of time are the people without a lot of other change or difficulty in their life. Things seem to be going well for them, they’re achieving their goals, and nothing much has changed. They think, ‘Why do I feel less satisfied than I expected to? Why is this going on year after year? Why does it seem to be getting worse and not better? There must be something wrong with my life.

‘Well, there’s nothing wrong with your life, you’re just feeling the effects of time which others who may have more turbulent lives may not notice as much.’

Rauch details a raft of research in his book to back up his claims. A 2008 study by economists David Blanchflower and Andrew Oswald found the U-curve – with the nadir, on average, at age 46 – in 55 of 80 countries, and they cited more than 20 other papers finding the U. It tends to show up in wealthier countries where people live longer, healthier lives.

Not all economists and psychologists agree. Economists Paul Frijters and Tony Beatton factored in the possibility that those who become happier in the studies are the same people who are more content when they start out. This can help them achieve greater career or relationship success, which leads to more happiness. Correcting for this effect, the U-shape disappears.

Rauch, however, believes he is a textbook example of the U-curve.

His mother suffered from depression and his parents broke up when he was 12, leaving his father to bring up three children on his own. Two years later, his father, a stressed and overworked lawyer in his mid-40s, lost his biggest client.

Rauch remembers himself at 20, keen to accomplish something worthwhile by middle age and believing that when he did, he’d appreciate it.

By his 40s, he had surpassed his dreams. He had published books; he was winning journalism prizes; he was in a relationship; he lived in an area of north Virginia with a strong sense of community. Yet he was preoccupied with what he had not achieved.

He explains: ‘I was someone who was fortunate. I had good health... I met one goal after another with more success than I’d ever expected.

‘Yet around the time I turned 40 I noticed this strange feeling of restlessness and discontent. This continued to grow as I got into my 40s to the point where I was 45 and I won the most prestigious award in magazine journalism [a National Magazine award] and that gave me a great feeling of satisfaction with my life for approximately 10 days.

‘All these feelings of discontent and restlessness – and even sometimes worthlessness and this feeling I’d almost wasted my life – kept coming back.

‘None of this made any rational sense. I began to think there must be something wrong with me. I began to think my personality had begun to turn dark in some way and that of course compounded the problem.’

Around 50, the fog began to lift, despite the death of both his parents, the loss of his magazine job and the failure of a startup venture. Rauch, 58, says: ‘In my 50s, first the volume of the demons’ voices went down, and now I rarely hear their voices at all.’

While researching his book, Rauch spoke to many people who’d experienced similar feelings.

Karla, 54, is on the upswing of the curve. She says she is savouring her friendships more, feeling more organised and efficient, and doing more volunteering work. ‘Now I feel grateful for the now,’ she tells Rauch. ‘On a day-to-day basis I probably do the same things, but I feel different.’

Rauch says: ‘That’s a very profound insight because what we’re talking about here is not that the conditions of your life change in some huge way, but how you feel about your life changes.’

Rauch puts forward various explanations for why we feel happier in our 50s and beyond.

Research shows that older people feel less stress and regret, dwell less on negative information and are better able to regulate their emotions. Nor is status competition as important. Rauch says: ‘We seem to be wired to seek maximum status when we are young – the ambition to be on top of the world, to have the big job, to have the extraordinary marriage to the wonderful person or lots of money. Or some form of greatness, which is what I dreamed of in my 20s, to write some book that would outdo Shakespeare.’

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We are over-optimistic in youth about how much satisfaction we will get out of our future successes, he believes. ‘As we get into our 30s and 40s, we’ve achieved most of those things, but we’re not wired to sit back and enjoy our status. ‘The same ambition that made us status hungry makes us hungry for more status. We’re on the hedonic treadmill. We don’t feel the satisfaction we expected, so we think there’s something wrong with our lives.’

As we get older, our values change. ‘You hear people say, ‘I don’t feel the need to check those boxes any more’, or ‘I don’t care that much what other people think’.’

Older people feel relieved of a burden that makes it easier to savour other simpler pursuits such as spending time with grandchildren, a hobby or volunteer work.

Rauch would like to see more help for people to relaunch themselves after this midlife transition, including greater opportunities for adult learning and companies creating more part-time positions or allowing gap years.

‘There’s a huge amount of untapped wisdom and potential to be unlocked. Because of the happiness curve, they’re often in a position where they want to give back. They want to be mentors, they want to be volunteers and they want to work at not-so-difficult jobs which allow them to use their skills.’

Rauch has a few tips for relieving midlife malaise, such as talking to friends about it and understanding it’s normal. It is also helpful to stop comparing yourself to others, he says.

But if all that makes no difference, give it time. As Rauch approaches 60, he feels ever more grateful for his life. He wishes he’d known this when he was in the trough of the curve because, as he says: ‘It’s worth the wait.’

Guardian.co.uk (c) Guardian News & Media Ltd, 2018