Research using four major international studies of twins suggests that eating more fruit and vegetables could help reduce depression. Although the benefit of high fruit and vegetable intake has previously been reported, few studies have focused on adults aged 45+, or specifically on twins.

The study, led by UNSW Sydney's Centre for Healthy Brain Ageing (CHeBA), assessed the associations between fruit and vegetable intake and depressive symptoms over 11 years, in 3,483 twins from Australia, Denmark, Sweden and the U.S.

Published in Scientific Reports, the findings revealed that higher intakes of both fruit and vegetables were associated with lower symptoms of depression over time.

Lead author and Post Doctoral Fellow Dr. Annabel Matison said, "The findings present another argument for increasing fruit and vegetable intake in adults over 45 years of age."

Depressive disorders significantly contribute to disease burden in adults over the age of 55, ranging from mild depression that doesn't reach the threshold of clinical diagnosis but still affects quality of life, to severe major depressive disorder. Individuals with major depression exhibit higher levels of pro-inflammatory and oxidative stress markers and diminished levels of antioxidant markers, when compared to healthy individuals.

The study has a number of strengths, in particular its twin design.

Co-author on the research and Leader of CHeBA's Genomics and Epigenomics Group, Dr. Karen Mather, says that twin studies provide a unique opportunity to address some of the limitations of previous observational studies.

"Twin pairs share 50–100% of their genetic background and, when raised together, share the same family environment. One of the advantages of the twin design is that it can help address the issue of unwanted factors, such as socioeconomic status early in life, influencing the results," Dr. Karen Mather said.

The study collected data from longitudinal twin studies who are all members of the Interplay of Genes and Environment across Multiple Studies (IGEMS) consortium, specifically, CHeBA's Older Australian Twins Study, Minnesota Twin Study of Adult Development and Aging, Middle Age Danish Twins Study and The Swedish Adoption/Twin Study of Aging.

Participants had to be 45+ at baseline with baseline fruit and vegetable intake data, baseline depression data and follow-up depression data.

In this research, low intake of fruit was on average 0.3 servings per day and low intake of vegetables was 0.5 servings per day; whereas high fruit intake was 2.1 servings per day and high vegetable intake was 2.0 servings per day. Interestingly, total fruit and vegetable consumption in the high category still fell notably below the dietary recommendations of most countries.

"We found that fruit and vegetable consumption in the two large Scandinavian studies were particularly low, with the average for both being less than half the World Health Organization recommended intake of at least 5 servings per day," said Dr. Matison.

"We are unclear what the reduction in depression scores would be if intakes were increased to recommended levels."

According to the researchers, the beneficial relationship between fruit and vegetable intake and depression is most likely due to high levels of dietary fiber, vitamins and micronutrients. Consumption of fruit and vegetables also appears to positively impact the composition of the gut microbiome and protect against oxidative damage to the brain.

"The importance of the gut microbiome and its potential influence on depression as a result of inflammation, both systemic and neuroinflammation, is becoming increasingly well understood," said Dr. Annabel Matison.