Background

Depressive disorders are a leading cause of disability in older adults, contributing to approximately 4% of years lived with disability among those aged 55 and older¹. The Prevalence appears to peak between the ages of 55 and 75 years, affecting around 8% of women and 5.5% of men². Symptoms can range from mild depression that negatively affects quality of life, to severe major depressive disorder.

Although the benefit of high fruit and vegetable intake has previously been reported in observational studies, few of these studies have focused on adults aged 45+, or specifically on twins. Twin studies provide a unique opportunity to address a limitation of previous observational studies which is that associations detected may be due to residual confounding. By studying twins, we reduce the influence of genetics and a range of environmental variables such as education, BMI and socio-economic status, given these factors are far more similar between twins than between unrelated participants.

Aim

The aim of this study was to examine the longitudinal associations between baseline fruit and vegetable intake and depressive symptoms over a period of up to 11 years in twins aged 45+ years from four international cohorts using linear mixed effect models.

Methods

The study examined twins aged 45+ from four countries - Australia, Denmark, Sweden, and the USA - participating in the IGEMS consortium. Participants reported their fruit and vegetable intake using food frequency questionnaires, which were then harmonised across cohorts.  Depressive symptoms were collected at baseline and follow-ups using validated depression assessment measures.

Researchers used linear mixed effects models to assess the relationship between fruit and vegetable intake and changes in depressive symptoms over time. Covariates adjusted for included age, sex, education, living alone status, BMI, physical health, and cognitive ability. A meta-analysis was conducted to combine results from all cohorts.

Results

A total of 3483 participants provided baseline fruit and vegetable intake, together with depression data at baseline and at least one follow-up.

For fruit, high intake was associated with a modest reduction in depressive symptoms compared to low intake. In contrast, no difference was detected for moderate intake. For vegetables, compared with low intakes, both moderate and high intakes were associated with lower depressive symptoms over time, with stronger effects seen for high intake.

Implications of the study 

Although the observed benefits were modest, they provide further evidence that higher fruit and vegetable intake may protect against depression. Our results indicate a high versus low intake of fruit (average of 1.8 more serves/day) is associated with a reduction in depressive symptoms of 0.29. For vegetables a high versus low intake (average of 1.5 more serves/day) is associated with a reduction in depressive symptoms of 0.27. However, total fruit and vegetable consumption in the “high” category still falls notably below the dietary recommendations of most countries. Intakes in the two large Scandinavian cohorts were particularly low, with the average for both cohorts being less than half the World Health Organization recommended intake of at least 5 serves per day. It remains unclear what the reduction in depression scores would be if intakes were increased to recommended levels.

The exact mechanisms behind these benefits are still being explored. However, it's likely that the high levels of dietary fibre, vitamins, and micronutrients in fruits and vegetables play a role in reducing inflammation and oxidative stress, both of which have been linked to depression. The importance of the gut microbiome to mental health is becoming increasingly well understood. Consumption of fruit and vegetables appears to beneficially impact the composition of the gut microbiome and protect against oxidative damage to the brain.

Limitations

Some limitations of the study include the lack of physical activity data and reliance on self-reported dietary and depression measures. Additionally, participants in this study generally had low baseline levels of depressive symptoms. It is possible that future studies in clinically depressed participants may shed more light on the associations.

Conclusion

This study adds to the growing body of evidence suggesting that higher fruit and vegetable intake may help protect against depression. Although the effects were modest, they present another argument for increasing intakes. Increasing fruit and vegetable consumption, especially in populations where intakes remain well below recommended levels, could offer a simple and accessible approach to supporting mental health.

Longitudinal associations between fruit and vegetable intakes and depressive symptoms in middle-aged and older adults from four international twin cohorts | Scientific Reports

References

1             Institute for Health Metrics and Evaluation. Global Health Data Exchange, <https://www.healthdata.org/> (2019).

2             World Health Organisation. Depression and other common mental disorders: global health estimates. (WHO, 2017).