By examining data collected from years of twin studies, scientists have found a correlation between the level of depressive symptoms and the amount of fruits and vegetables consumed daily.
The twin method is one of the most effective approaches for determining the influence of genetic factors and environmental conditions on the development of various character traits, behaviors, and predispositions to disease.
Due to the fact that identical twins are characterized by a nearly identical set of genes, and identical twins share about 50% of their genetic material, differences between them are most often attributed to the unique life experiences of one that the other did not have.
A new international study organized by the Centre for Healthy Brain Aging (CHeBA) at the University of New South Wales in Sydney (UNSW) examined the association between fruit and vegetable consumption and the occurrence of symptoms of depression in twins over the age of 45.
"Twin pairs share 50-100% of the same genetic background and, when raised together, share the same family background," said Dr. Karen Mazer, CHeBA genomics and epigenomics group leader and senior author of the study. "One of the advantages of the twin method is that it addresses the influence of undesirable factors, such as socioeconomic status early in life, on outcomes."
More fruits and vegetables
Every child's parents used to say the phrase, "You should eat more fruits and vegetables". This fact is scientifically proven, unlike more dubious parental claims, such as that eating bread crusts will make your hair curly.
Although there is a growing body of evidence on the effects of diet on mental health, including the occurrence of
depression, few studies have examined how fruit and vegetable consumption affects people over the age of 45. Even fewer have taken advantage of the unique opportunity offered by the twin method, which reduces the influence of genetic and environmental factors on the study.
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So in a new study, scientists set out to examine the association between baseline fruit and vegetable consumption and symptoms of depression in 3,483 twins over the age of 45. They used data from four longitudinal twin studies of approximately 11 years' duration that were conducted in Australia, Denmark, Sweden and the United States.
The study collected data on fruit and vegetable consumption divided into three categories: low, moderate, and high. For fruits, low consumption averaged 0.3 servings per day and high consumption averaged 2.1 servings. In the case of vegetables, low consumption was 0.5 servings per day and high levels reached 2.0 servings. Tested and validated techniques were used to assess depressive symptoms in participants, both at baseline and at follow-up.
The results showed that regular consumption of large amounts of fruits and vegetables was associated with reduced manifestations of depression in the long term, especially when compared to low consumption. Notably, even moderate consumption of vegetables, as opposed to fruit, had a marked positive effect in reducing depressive symptoms.
"Our findings add another argument for increasing the proportion of fruits and vegetables in the diet of adults over 45 years of age," notes Dr. Annabel Matheson, lead researcher and author of the paper.
Conclusions and perspectives of the study
The authors of the study emphasize that even those in the "high" consumption group consumed fewer fruits and vegetables than recommended by nutritionists in most countries. This led scientists to wonder how much more powerful the effect could be if people at least reached the recommended guidelines.
"Our analysis showed that in two large-scale Scandinavian studies, fruit and vegetable intake was well below recommended guidelines: on average, people consumed less than half of the World Health Organization's minimum of five servings per day," Matheson commented. "We are left to speculate how much more markedly depression symptoms might have been reduced if participants had achieved the recommended amount of fruit intake."
The researchers suggest that the positive effects of fruits and vegetables on mental health are related, at least in part, to the state of the gut microbiome.
This area of medical research is being actively studied, and a growing body of evidence points to its key role in regulating mood and emotional well-being. "The importance of the gut microbiome and its potential impact on depression as a result of inflammation, both systemic and neuroinflammation, is becoming increasingly clear," says Matheson.
However, the study that was conducted had limitations. Researchers were unable to adjust for physical activity because this data was not available in all studies. Another limitation was that the studies used different questionnaires to record dietary intake and self-reported symptoms of depression, whereas the gold standard for assessing depression is clinical diagnosis.
In contrast, there are strengths, particularly the twin method, which has reduced the influence of a number of potential factors such as socioeconomic status, physical activity, and chronic disease.
Future studies should address these limitations by using comprehensive, standardized instruments to collect data on fruit and vegetable consumption, in addition to clinical assessment of symptoms of depression.
The researchers say that based on the findings, health care providers should monitor the fruit and vegetable intake of their patients, especially those with depressive symptoms.