People who adopt four principles for a healthy lifestyle can add as much as 14 years to their lives, a major study revealed today.

The four "healthy behaviours" - giving up smoking, taking exercise, drinking in moderation and eating five servings of fruit and vegetables a day - can have a huge impact on life expectancy, researchers at Cambridge University found.

The Public Library of Science Medicine study published in the journal PLoS Medicine is one of the first to look at the combined impact of the four factors on life expectancy.

It followed the health of 20,000 men and women aged between 45 and 79 from Norfolk between 1993 and 2006. At the start of the study none of the participants was known to have cancer or heart disease.

The study showed that a person's social class or body mass index did not have a role to play in their life expectancy.

It said: "The results of the study strongly suggest that these four achievable lifestyle changes could have a marked improvement on the health of middle-aged and older people, which is particularly important given the ageing population in the UK and other European countries."

People taking part in the study were awarded a point for each of the four healthy behaviours: not smoking, not being physically inactive (physical inactivity was defined as having a sedentary job and not doing any recreational exercise), drinking less than 14 units of alcohol (seven pints of beer) a week and having a vitamin C level equivalent to eating five servings of fruit or vegetables a day.

After factoring in age, the results showed that over an average period of eleven years people with a score of 0 - those who did not undertake any of these healthy forms of behaviour - were four times more likely to have died than those who had scored 4 in the questionnaire.

Furthermore, the res- earchers calculate that a person who has a health score of 0 has the same risk of dying as someone 14 years older who had scored 4 in the questionnaire for engaging in all four healthy behaviours.