London: People who eat plenty of fruit and vegetables tend to be more optimistic about the future, according to Harvard scientists.
Scientists have discovered that optimistic people have higher levels of plant compounds called carotenoids in their blood.
A commonly-known carotenoid is beta-carotene, a pigment found in high levels in orange fruit and veg and green, leafy vegetables, the `Daily Mail` reported.
Previous studies have shown that high blood levels of antioxidants - of which carotenoids are one form - may be a marker of good health.
Antioxidants help keep other molecules in the body from producing free radicals, which can damage cells and contribute to disease.
"Individuals with greater optimism tended to have greater levels of carotenoids such as beta-carotene," said lead investigator Julia Boehm, of the Harvard School of Public Health.
"This is the first study of its kind to report a relationship between optimism and healthier levels of carotenoid concentrations," she added.
One theory is that antioxidants might have a de-stressing effect.
The current study evaluated blood concentrations of nine different antioxidants, including carotenoids such as beta-carotene and vitamin E in nearly 1,000 American men and women ages 25 to 74.
Participants filled out a questionnaire about their life attitudes and provided blood samples to the researchers, according to the report in Psychosomatic Medicine.
They also measured the degree of optimism in the same group.
Researchers found that people who were more optimistic had up to a 13 per cent increase in carotenoid concentrations in their blood compared with people who were less optimistic.
The researchers believe that higher levels of fruit and vegetable consumption among more optimistic people may at least partially explain the results.
They found that people who ate two or fewer servings of fruits and vegetables a day were significantly less optimistic than people who ate three or more servings a day.
They added that the relationship between optimism and carotenoid levels was only partially explained by the fact that more optimistic people tended to engage in healthier behaviours such as eating fruits and vegetables and avoiding cigarette smoking.
Last year, scientists at Warwick University found that people who ate seven portions of fruit and veg a day are the happiest.
The study found that those who ate around eight portions of fruit and vegetables a day had an average score that was one point higher than people who did not eat any.