Fruit, Veg Consumption May Lower Psychological Stress

Nancy A. Melville

March 28, 2017

Consumption of fruits and vegetables, either separately or combined, is linked to a lower prevalence of psychological stress primarily in women, results of a large longitudinal study suggest.

"Our study, which is based on a large sample of more than 60,000 Australians, adds to the limited evidence base for a longitudinal association between mental well-being and fruit and vegetable intake. Our study is also novel in that it compares findings in men and women," first author Binh Nguyen, a PhD candidate and research officer in the Prevention Research Collaboration at the Sydney School of Public Health, University of Sydney, in Australia, told Medscape Medical News.

The study was published in the March issue of BMJ Open.

Moderate Consumption

The study included 60,404 adults aged 45 years and older enrolled in the Sax Institute's 45 and Up Study. The participants completed surveys at baseline between 2006 and 2008 and were followed up in 2010.

The mean age of the participants was 62.2 years, and 53.6% were women. They reported consuming 2.0 mean daily servings of fruit and 3.9 mean daily servings of vegetables.

At a mean follow-up of 2.7 years, higher baseline levels of fruit and vegetable consumption, compared to one or no servings per day, were significantly associated with a lower prevalence of high to very high levels of psychological distress, defined as a score of 22 or higher on the 10-item validated Kessler Psychological Distress Scale (K10) (P = .01 - < .001), after adjustment for sociodemographic and lifestyle risk factors.

Compared to those who consumed the lowest levels per day, those who consumed three to four daily servings of vegetables showed a 12% reduced risk for stress; those who ate five to seven servings of fruit as well as vegetables had a 14% lower risk for stress compared to those who consumed 0 to four servings per day.

"Consumption of fruit and vegetables, considered separately or combined, was consistently associated with a lower prevalence of psychological distress. Following adjustment for all covariates, these associations were slightly attenuated compared with the unadjusted model but remained significant," the researchers write.

However, a longitudinal analysis showed that after full adjustment for confounders, the association was only significant with medium consumption, not high consumption.

In addition to age and sex, factors in the fully adjusted analyses included body mass index, smoking status, alcohol intake, physical activity, chronic disease, income, and education.

Further analysis stratifying the effects in women and men showed that the association with reduced stress was only significant in women (P ≤ .001).

Women who consumed three to four daily servings of vegetables had an 18% reduced risk for stress compared to women who consumed 0 to 1 servings daily; those who consumed two servings of fruit had a 16% risk reduction, and those who ate five to seven servings of fruits and vegetables combined had a 23% lower risk for stress.

"We did not expect to see these striking differences between men and women. We don't really know the reasons behind this, but perhaps women are better at reporting their fruit and vegetable intake," Nguyen said.

Surprise Finding

The finding that only medium consumption, but not high consumption of vegetables and fruits was associated with reduced stress was also a surprise, said Nguyen.

"Those who consume higher amounts of fruit and vegetables may also have been consuming big quantities of other types of foods which could lead to psychological distress," Nguyen said.

Mechanisms that could explain the link between fruit and vegetable consumption and overall psychological well-being include their rich compositions of micronutrients and phytochemicals, resulting in a reduction in oxidative stress and inflammation that are linked to mental health disorders, the authors speculate.

"Although more research is needed, potential mechanisms include that fruit and vegetables are high in antioxidants such as vitamins C and E. These can help reduce oxidative stress and inflammation, which can be harmful to mental health," Nguyen.

Other large studies have shown inverse associations with psychological well-being. A recent meta-analysis of studies of fruit and vegetable consumption showed an inverse association with rates of depression.

In addition, a recent Swiss survey of 20,220 adults showed that a daily recommended intake of five servings of fruit and vegetables was associated with a lower rate of high or moderate psychological distress.

However, not all studies have shown psychological benefits after adjustment for the other healthy lifestyle factors that could be expected to accompany regular vegetable and fruit consumption.

For example, a longitudinal study of more than 8000 Canadians that was published last year in the BMJ showed improvement in depression and psychological distress linked to daily consumption of fruit and vegetables, but the association lost significance after the reseachers adjusted for other health-related factors, including smoking and physical activity.

"These findings suggest that relations between fruit and vegetable intake, other health-related behaviours and depression are complex," the authors of that study conclude.

"Behaviors such as smoking and physical activity may have a more important impact on depression than fruit and vegetable intake," they add.

The study received funding from a development award from the Cardiovascular Research Network of New South Wales. The authors have disclosed no relevant financial relationships.

BMJ Open. 2017;7:e014201. Full text


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