The Mediterranean diet (MD) is a popular and medically accepted diet for weight management and health promotion; however, the potential mental health benefits associated with this diet remain unclear. A new study in the British Journal of Nutrition discusses the association between MD and depressive symptoms in a cohort of older men and women.
Study: Adherence to Mediterranean diet is inversely associated with depressive symptoms in older women: findings from the NutBrain Study. Image Credit: PeopleImages.com - Yuri A / Shutterstock.com
Depression and aging
Current estimates indicate that about 5% of the global population suffers from depression, with depression among the leading causes of disability throughout the world. Importantly, the prevalence of depression increases with age, with one-third of older people affected.
Women are at greater risk for depressive symptoms from adulthood onwards, with this risk further increasing after the age of 60 years. In Italy, 10% of people over 65 years of age report depressive symptoms, with up to 14% of women 85 years and older experiencing depression.
Biological, psychological, social, and environmental factors contribute to the development of depression; therefore, diet can be considered a modifiable risk factor for this condition. Previous research has shown that following the MD is related to a lower risk of depressive symptoms overall.
The current study examined the association between MD, due to its ideal nutritional and antioxidant profile, and depressive symptoms. More specifically, the researchers were interested in clarifying the existence of this association, and especially sex-related differences, in older people, with the added contribution of separating these associations by dietary components.
Data were obtained from a food frequency questionnaire intended to semi-quantitatively assess adherence to the MD in the form of the Mediterranean diet score (MDS) and a depression measurement scale. Study participants were part of the population-based community-dwelling Nutrition, Gut Microbiota, and Brain Aging (NutBrain) cohort, and the study was conducted from October 2019 to January 2023.
What did the study show?
A total of 325 men and 473 women were included in the study, 60% of whom were between 65 and 74 years of age. The mean age was 73 years, with about 66% of study participants married and living with others, whereas 50% were considered underprivileged.
About 20% of the study cohort suffered from depressive symptoms, with 8% of men and 28% of women reporting depressive symptoms. Men with and without depression differed only in the significantly greater number of medications used in those with depression.
Among women, unmarried women, those living alone, those prescribed more drugs, and those who considered themselves to be sicker were more likely to experience symptoms of depression, as were those who ate less fish, vegetables, and healthy fats relative to saturated fat. About 33% of men reported adherence to the MD compared to 25% of women.
Study participants with the top third of MDS scores were 55% less likely to report depressive symptoms. When stratified by sex, women with the top third of MDS scores were at a 60% reduced risk of depression.
High fish consumption was associated with a 44% reduced risk of depressive symptoms in men and women. When stratified by sex, women with high fish consumption were 56% less likely to experience depressive symptoms. With each additional gram of fish consumption, the likelihood of depression declined by 2% overall and in women but not men.
The type of fish associated with a reduced risk of depression when three or more servings were consumed each week included shellfish, sole, trout, sea bream, cod, hake, and sea bass. This reduction was 62% overall for fish and 4% for shellfish.
When stratified by sex, women were associated with a reduced risk of depression by 43% with two to three servings of these fish each week; however, this risk further declined by 70% with three or more servings each week as compared to those consuming two or fewer servings of fish. This association was not observed in men.
Women with a high ratio of monounsaturated fatty acids to saturated fatty acids (MUFA/SFA) in their diet were 42% less likely to report depressive symptoms. For both men and women, nut and fruit consumption was associated with a reduced risk of depressive symptoms by 82% and 42%, respectively.
With each one-point increase in MDS, the risk of depressive symptoms decreased by 16% overall and by 18% in women. When only men were considered, this reduction was not significant.
What are the implications?
Adherence to the highest tertile of the MD is inversely associated with depressive symptoms and, in particular, this is only evident in women.”
The negative association of the MD, particularly fresh fish and higher MUFA/SFA, with depression corroborates earlier research.
The association of fresh fish with a reduced risk of depressive symptoms could be due to reduced inflammation, regulation of hypothalamic and pituitary hormones, which regulates other endocrine functions, reduced oxidative stress, gut microbiota profile, as well as other metabolic and intracellular pathways related to mental health.
The differential effects in women may be due to a higher prevalence of vitamin D deficiency in women, which is associated with poor mental health, including depression and psychosis, as well as changes in brain cell membranes caused by the supply of omega-3 fatty acids abundant in the MD. However, further research is needed to confirm these hypotheses.
While these findings cannot be experimentally confirmed, and the inclusion of study subjects may show multiple biases, the study cohort was representative of the older community in each locality. Despite these limitations, the study findings emphasize the key role of a healthy diet in promoting mental health in older people. Thus, public health efforts towards this goal will likely be productive, even as further studies are conducted to understand the biological processes responsible for these benefits.
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