N-3 and N-6 Fatty Acid Intake Inversely Associated with Risk of Depressive Symptoms

Written by Angeline A. De Leon, Staff Writer. Intakes of n‐3 and n‐6 fatty acids were inversely associated with the risk of depressive symptoms, and the n‐6:n‐3 ratio was positively associated with the risk of depressive symptoms.

Recent statistics place depression as one of the top contributors to global disability and mortality ¹. One variable known to play an important role in the development of depression is nutrition, as epidemiological studies link intake of certain foods, namely fruits, vegetables, and fish ^2,3, as well as certain nutrients like magnesium, zinc, and selenium ⁴, with reduced risk for depression. Within this category, polyunsaturated fats (n-3 and n-6 fatty acids) have been related to depression ⁵, with higher dietary intake of n-3 fatty acids specifically showing a protective effect of lowering risk of depression ⁶. Findings in relation to n-6 fatty acids are less consistent ⁷, with some research suggesting that n-6 fatty acid intake may actually increase risk of severe depression ⁸. The role of n-6: n-3 ratio in the development of depression is also unclear, and while some research suggest there is no relationship to depressive symptoms ⁶, others report a positive association ⁹. To clarify the nature of the relationship of fatty acid intake and risk of depression, a 2020 study ¹⁰ published in Nutrients examined the dose-response association between n-3 fatty acids, n-6 fatty acids, and n-6: n-3 ratio and symptoms of depression in American adults.

A total of 17,431 subjects (40.2% aged 18-44 years; 31% aged 44-59 years; 28.7% aged 60 years and older) were enrolled in a prospective, cohort-based, cross-sectional study. Participants were administered the Nine-Item Patient Health Questionnaire (PHQ-9), and dietary n-3 and n-6 fatty acid intake were evaluated using two 24-hour dietary recall interviews (adjusted by energy). Regression analyses were conducted to assess the associations between dietary n-3 and n-6 fatty acids and n-6: n-3 ratio with depressive symptoms. Adjusted dietary n-3 and n-6 fatty acid intake were divided into tertiles, as was dietary n-6: n-3 ratios, and Odds Ratios (OR) were calculated.

Analyses revealed that, after adjusting for covariates (age, gender, body mass index, energy intake, etc.), the ORs for the highest tertile of n-3 fatty acids and n-6: n-3 ratio were 0.70 (95% Confidence Interval: 0.55 to 0.92) and 1.66 (95% CI: 1.10 to 2.40), respectively, compared to the lowest tertile (reference group). OR for the middle tertile of n-6 fatty acids, compared to the reference group, was 0.72 (95% CI: 0.56 to 0.92). A U-shaped association was found between n-3 fatty acid intake and risk of depressive symptoms such that OR was lowest when n-3 fatty acid intake was 1.1 mg/kcal/day (OR = 0.45). A similar U-shaped association was found for n-6 fatty acid intake such that OR was lowest when n-6 fatty acid intake was 8.8 mg/kcal/day (OR = 0.59). N-6: n-3 ratio was found to be positively associated with risk for depressive symptoms in a linear fashion.

Based on study findings, intake of n-3 and n-6 fatty acids both appear to be inversely associated with risk of depressive symptoms, while n-6: n-3 ratio was found to be positively linked to risk of depressive symptoms. Although findings in relation to n-3 fatty acids seems in line with previous research ⁶ the inverse relationship between n-6 fatty acid intake and depressive symptoms is inconsistent with the literature ⁸, which warrants further exploration. While fatty acid intake may play a useful role in supporting emotional wellbeing, the exact mechanisms underlying its therapeutic effects also requires additional research. Study limitations to consider are the cross-sectional design of the current study, which prohibits determination of causality, and the uncertainty associated with using recall interviews to assess daily dietary intake.

Source: Zhang R, Sun J, Li Y, et al. Associations of n-3, n-6 fatty acids intakes and n-6: n-3 ratio with the risk of depressive symptoms: NHANES 2009-2016. Nutrients. 2020; 12: 240. DOI: 10.3390/nu120102040.

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)

Posted March 23, 2020.

Angeline A. De Leon, MA, graduated from the University of Illinois at Urbana-Champaign in 2010, completing a bachelor’s degree in psychology, with a concentration in neuroscience. She received her master’s degree from The Ohio State University in 2013, where she studied clinical neuroscience within an integrative health program. Her specialized area of research involves the complementary use of neuroimaging and neuropsychology-based methodologies to examine how lifestyle factors, such as physical activity and meditation, can influence brain plasticity and enhance overall connectivity.

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