Fruit and vegetable consumption and psychological distress: cross-sectional and longitudinal analyses based on a large Australian sample
Diet and mental health
Mental health disorders currently account for the greatest burden of disability worldwide and a third of the global burden of non-fatal diseases1. Public health prevention strategies are urgently needed. There has been growing interest in examining the role of diet in mental health. Observational studies have generally shown a positive association between an overall healthy eating pattern (consistent with the “Mediterranean diet”; based on diets high in fruit and vegetables (F&V), unprocessed grains and fish, and low in processed foods) and mental wellbeing2-5.
The role of F&V consumption in mental health has received increasing attention. Fruits and vegetables are rich in nutrients, and their protective effects in relation to several chronic diseases are well known6-7. In addition, diets low in fruit have been reported to be the leading dietary risk factor for the global burden of disease8. There is also growing evidence, particularly from cross-sectional studies, which suggests a potential link between fruit and vegetable consumption and psychological distress9. However, to build stronger evidence, more prospective studies are needed10-11. Therefore, this study aimed to examine the association between F&V consumption and both the prevalence and incidence of psychological distress in a large cohort of Australian adults.
Study population and measurements
Baseline (2006-2008) and follow-up (2010) questionnaires were completed by participants aged 45 years and over (60,404 for crosssectional analyses and 54,345 for prospective analyses) from the Sax Institute’s 45 and Up Study (https://www.saxinstitute.org.au/our-work/45- up-study/). Psychological distress was assessed using the validated Kessler Psychological Distress Scale (K10) which measures anxiety and depression symptoms12-13. Usual F&V consumption was assessed using validated short questions.
Cross-sectional analyses: prevalence of psychological distress
At baseline, 5.6% of participants reported psychological distress. Baseline F&V consumption, together or separately, was associated with a lower prevalence of psychological distress, even after adjusting for sociodemographic characteristics and lifestyle risk factors.
Prospective analyses: incidence of psychological distress
After a three-year follow up, 4.0% of those who did not report distress at baseline reported distress at follow-up. The prospective association between F&V consumption and psychological distress was less consistent, although generally in the same direction as findings from previous studies. Moderate daily F&V consumption was associated with lower odds of psychological distress. For example, people who ate 5-7 daily serves of F&V had 14% lower odds of psychological distress than those who ate 0-4 serves daily. Overall, our study’s findings were consistent with those from several cross-sectional studies and a limited number of prospective studies.
Differences between men and women
The more novel, additional analyses in men and women, surprisingly showed that F&V consumption was more protective for women. There were no clear associations in men over the three-year follow-up period. A mechanism that could explain a true physiological difference between men and women remains unclear and requires further investigation. Women may have more accurately reported their consumption than men, and this may have contributed to the differences observed.
Potential mechanisms linking fruit and vegetables to mental health
Fruit and vegetables are high in antioxidants (e.g. vitamins C and E) that can help reduce oxidative stress and inflammation, which can be harmful to mental health. Additionally, B-vitamin deficiencies (e.g. folic acid or vitamin B9) influence mood regulation and have been associated with depression. Prebiotic foods have also been linked to improved mental health. F&V may therefore affect several biological pathways related to mental health; however, more studies are needed.
Study implications and conclusions
In interpreting this study’s findings, several points should be highlighted:
- The study questionnaire was limited in its dietary assessment and there may have been residual confounding from dietary/non-dietary factors.
- Assuming that there was a causal link, the direction of the associations could not be inferred. We tried to minimise the possibility of “reverse causation” (i.e., that poor mental health leads to a poor diet) by excluding participants who were being treated for depression/anxiety, were taking antidepressants, or reported being psychological distressed.
- Causality could not be inferred from this observational study.
- Those who consume healthy amounts of F&V may also be engaging in other healthy lifestyle behaviours which together could have contributed to lower psychological distress.
Among this cohort of middle-aged and older adults, F&Vconsumption may help reduce the prevalence of psychological distress. Our longitudinal findings contribute to the limited evidence base for an association between F&V consumption and the incidence of psychological distress. Whilst our findings lend support to existing public health guidelines that promote F&V consumption as part of a healthy diet, further longitudinal studies are needed.
Based on: Nguyen B, Ding D, Mihrshahi S. Fruit and Vegetable Consumption and Psychological Distress: Cross-Sectional and Longitudinal Analyses Based on a Large Australian Sample. BMJ Open 2017;7:e014201. doi:10.1136/bmjopen-2016-014201
- Whiteford HA et al. PLoS ONE 2015;10(2):e0116820. doi:10.1371/journal. pone.0116820
- Lai JS et al. The Am J Clin Nutr 2014;91:747–770. doi:10.3945/ajcn.113.069880
- O’Neil A et al. Am J Public Health 2014;104(10): e31–e42. doi:10.2105/AJPH.2014.302110
- Psaltopoulou T et al. N. Ann Neurol 2013;74(4):580–591. doi:10.1002/ana.23944
- Sanchez-Villegas A et al. Arch Gen Psychiatry 2009; 66(10):1090–1098. doi:10.1001/archgenpsychiatry.2009.129
- Wang X et al. BMJ 2014;349:g4490. doi:10.1136/bmj.g4490
- World Cancer Research Fund and the American Institute for Cancer Research. Washington, DC: American Institute for Cancer Research, 2007.
- Lim SS et al. The Lancet 2012;380:2224–2260. doi:10.1016/S0140-6736(12)61766-8
- Liu X, Yan Y, Li F, Zhang D. Nutrition 2016;32 :296-302. doi:10.1016/j. nut.2015.09.009
- Kingsbury M et al. J Epidemiol Community Health 2016;70:155–161. doi:10.1136/jech-2015-205858.
- Mihrshahi S, Dobson AJ, Mishra GD. Eur J Clin Nutr 2015;69(5):585-591.
- Andrews G, Slade T. Interpreting scores on the Kessler Psychological Distress Scale (K10). Australian and New Zealand Journal of Public Health 2001;25:494-7.
- Kessler RC et al. Arch Gen Psychiatry 2003;60(2):184-189.