People who stick to five healthy habits in adulthood can add more than a decade to their lives, according to a major study into the impact behaviour has on lifespan.

Researchers at Harvard University used lifestyle questionnaires and medical records from 123,000 volunteers to understand how much longer people lived if they followed a healthy diet, controlled their weight, took regular exercise, drank in moderation and did not smoke.

When the scientists calculated average life expectancy, they noticed a dramatic effect from the healthy habits. Compared with people who adopted none of them, men and women who adhered to all five saw their life expectancy at 50 rise from 26 to 38 years and 29 to 43 years respectively, or an extra 12 years for men and 14 for women.

“When we embarked on this study, I thought, of course, that people who adopted these habits would live longer. But the surprising thing was how huge the effect was,” said Meir Stampfer, a co-author on the study and professor of epidemiology and nutrition at the Harvard TH Chan School of Public Health.

The researchers performed the analysis in the hope of understanding why the US, which spends more on healthcare as a proportion of GDP than any other nation, ranks 31st in the world for life expectancy at birth. According to the World Health Organization, life expectancy at birth in 2015 was 76.9 and 81.6 years old for US men and women respectively. The equivalent figures for Britain are very similar at 79.4 and 83 years old.

The study, published in the journal Circulation, suggests poor lifestyle is a major factor that cuts American lives short. Only 8% of the general population followed all five healthy habits. The research focused on the US population, but Stampfer said the findings applied to the UK and much of the western world.

The five healthy habits were defined as not smoking; having a body mass index between 18.5 and 25; taking at least 30 minutes of moderate exercise a day, having no more than one 150ml glass of wine a day for women, or two for men; and having a diet rich in items such as fruit, vegetables and whole grains and low in red meat, saturated fats and sugar.

Men and women who had such healthy lives were 82% less likely to die of heart disease and 65% less likely to die of cancer compared with those with the least healthy lifestyles, over the roughly 30 years of the study.

Given that the habits of a healthy lifestyle are well known, the mystery is why we are so bad at adopting them, said Stampfer. Part of the problem is that many people struggle to give up smoking, and the continuous peddling of unhealthy food, as well as poor urban planning, which can make it hard for people to exercise, also feed in, he said.

“I do think people need to step up and take some personal responsibility, but as a society we need to make it easier for people to do that,” he said. “People can get stuck in a rut and think it’s too late to change their ways, but what we find is that when people do change their ways, we see remarkable benefits.”