The Human Life Cycle: Start Happy-Get Grumpy-Finish Happy
While young adults are carefree and full of hope for the future and the over-50s have come to terms with the trials of life, the research indicates that those in the middle feel weighed down by the demands on them.
The study found "a substantial dip in happiness during the middle of people's lives is the equivalent to becoming unemployed or losing a family member".
The conclusions come in a study of how people perceive their wellbeing.
Mr van Landeghem, who is 29, will present his research at the Royal Economic Society annual conference at Royal Holloway, the University of London, this week.
While he said happiness did return with age, he warned that older people did not actually recapture the spirit of their youth. They simply learnt to be satisfied with their lot.
"A U-shaped happiness curve does not necessarily imply that a 65 year-old prefers his own life to the life of a 25 year-old," he said. "Both the 25 year-old and 65 year-old might agree that it is nicer to be 25 than to be 65. But the 65 year-old might nevertheless be more satisfied, as he has learned to be satisfied with what he has."
Studies around the world have shown that happiness tends to dip in midlife, he said, and that this was not just a phenomenon confined to the Western world.
Last month, Lewis Wolpert, emeritus professor of biology at University College London, said happiness could peak as late as 80. In a book called You're Looking Very Well, Prof Wolpert said most people were "averagely happy" in their teens and 20s, but this declined until early middle age as they attempted to support a family and career.
He added: "From the mid-40s, people tend to become ever more cheerful and optimistic, perhaps reaching a maximum in their late 70s or 80s."
An easing of the responsibilities of middle age, maturity and an increased focus on the things we enjoy contributed to the trend, he said.
According to a study by the American National Academy of Sciences, based on a survey of 341,000 people, enjoyment of life begins an upward trend in the late 40s and does not peak until 85.
Older people today can benefit from better health and opportunities than previous generations, and research also suggests that our command of language and ability to make decisions increase with age.
Our capacity to concentrate on the parts of life and activities we enjoy, while cutting out things that we dislike, is also said to increase with age.
Meanwhile, the ageing population means an increasing number of middle-aged adults are caught between the responsibilities of raising their children and looking after their elderly parents