Research ReportDoes reverse causality explain the relationship between diet and depression?
Introduction
In both cross-sectional and prospective observational studies, better diet quality is associated with a reduced risk for, or prevalence of, depressive illness (Lai et al., 2013, Psaltopoulou et al., 2013). For example, we recently examined the cross-sectional and longitudinal associations between dietary patterns and symptoms of depression in a large ongoing cohort study of Australian adults and undertook a detailed examination of potential explanatory factors, particularly socioeconomic circumstances, in the diet–depression relationship (Jacka et al., 2014). In this study, we found that contemporaneous associations between depression and both a prudent dietary pattern (inverse) and a ‘western’ unhealthy dietary pattern (positive) were explained by adjustment for detailed measures of socioeconomic circumstances and physical activity. In prospective analyses, however, lower scores on the healthy dietary pattern and higher scores on the unhealthy dietary pattern independently predicted increased depressive symptoms across time, before and after adjustment for these confounders and baseline depressive symptoms, but only in the oldest cohort of participants. These findings are concordant with previous prospective studies examining the influence of diet on depression risk (Akbaraly et al., 2009, Akbaraly et al., 2013, Jacka et al., 2011, Lucas et al., 2013, Sanchez-Villegas et al., 2009).
However, relationships between diet and depression may be explained by ‘reverse causality’, wherein a change in dietary choices is prompted by depressive symptoms; diminished appetite is a symptom of major depression for many and there is also evidence to suggest that some with depression are more likely to consume high fat and sugar foods (Whitaker et al., 2014) and fewer fruits and vegetables (Payne et al., 2012). Although previous prospective studies have not found evidence to support the reverse causality hypothesis (e.g. (Akbaraly et al., 2009; Jacka et al., 2011; Sanchez-Villegas et al., 2009)), the relationship between diet and mental health is complex and likely bidirectional. Thus, further investigation of this association is warranted. We aimed to investigate reverse causality in the same large, ongoing cohort study of Australian adults examined previously (Jacka et al., 2014), hypothesising that those with a history of depression would have poorer diet quality than those without such a history, having controlled for current depression and other potentially confounding variables.
Section snippets
Methods
The methods and sample (n=3668) used in this study have been published in detail in our previous study (Jacka et al., 2014). Briefly, adults aged in their 20s, 40s and 60s were randomly recruited from the electoral roles to participate in the Personality and Total Health (PATH) Through Life Study in the ACT, Australia. All participants gave written informed consent prior to each wave of data collection in the Personality and Total Health (PATH) Through Life Study project. The study was approved
Results
There were 343 respondents (9.4%) classified as likely current depression cases based on their scores on the Goldberg scale. Using retrospective data on reported history of depression prior to baseline, 1571 respondents (43.1%) reported an episode of depression prior to their commencement in the PATH survey. Of these, 17.4% (273) were also classified as likely current depression cases. Regressing scores on the prudent dietary pattern scale onto both past and current depression, with age
Discussion
In this study investigating dietary patterns and depression there was evidence of reverse causality; however, the findings were counterintuitive. Individuals who had been previously depressed and sought treatment had higher scores on the healthy dietary pattern at the baseline assessment, although those with contemporaneous depression had lower scores on this dietary pattern. Moreover, those who had reported prior, but not current, depression at the time of the baseline assessment had lower
Limitations
The reliance on self-reported measures of prior depression limits the ability to form firm conclusions from this study. The potential for recall bias in the reporting of prior depression is well-recognised, particularly if episodes occurred more distally (Andrews et al., 1999). However, while we were reliant on retrospective reporting, self-awareness and willingness to disclose, the validity of these measures of prior depression is supported by evidence that 88% of respondents who reported
Conclusion
Results of this study did not support the hypothesis that a history of depression would be associated with poorer diet quality at a later timepoint. This finding suggests that reverse causality is not necessarily the explanation for relationships commonly observed between long-term diet quality and depression in adults. Indeed, while current depression is associated with poorer dietary habits, a history of depression may prompt healthier dietary behaviours in the long term. Given the
Role of funding source
This study was supported by NHMRC Grants no. 973302, Programme Grants no. 179805 and 350833, and NHMRC project Grant no. 157125. KJA is funded by NHMRC Research Fellowship no. 1002560. NC is funded by an ARC Future Fellowship No. 120100227. FNJ is funded by Deakin University. The funders played no role in the design or conduct of this study.
Conflicts of interest
There are no conflicts of interests to disclose.
Acknowledgements
The authors are grateful to Anthony Jorm, Bryan Rodgers, Helen Christensen, Simon Easteal, Patricia Jacomb, Karen Maxwell, and the PATH interviewers and participants.
References (25)
Adherence to healthy dietary guidelines and future depressive symptoms: evidence for sex differentials in the Whitehall II study
Am. J. Clin. Nutr.
(2013)After daily bingeing on a sucrose solution, food deprivation induces anxiety and accumbens dopamine/acetylcholine imbalance
Physiol. Behav.
(2008)The effect of food intake on mood
Clin. Nutr.
(2001)Fruit, vegetable, and antioxidant intakes are lower in older adults with depression
J. Acad. Nutr. Diet.
(2012)Depressive symptoms are associated with dietary intake but not physical activity among overweight and obese women from disadvantaged neighborhoods
Nutr. Res.
(2014)Dietary pattern and depressive symptoms in middle age
Br. J. Psychiatry
(2009)Recall of depressive episode 25 years previously
Psychol. Med.
(1999)Cohort Profile: the PATH through life project
Int. J. Epidemiol.
(2012)Detecting anxiety and depression in general medical settings
BMJ
(1988)- et al.
Depression, diet and exercise
MJA Open
(2012)
Dietary patterns and depressive symptoms over time: examining the relationships with socioeconomic position, health behaviours and cardiovascular risk
PLoS One
A prospective study of diet quality and mental health in adolescents
PLoS One
Cited by (118)
Global and Epidemiological Perspectives on Diet and Mood
2024, The Gut-Brain Axis, Second EditionAssociations between diet quality and anxiety and depressive disorders: A systematic review
2023, Journal of Affective Disorders ReportsAssociation between niacin intake and depression: A nationwide cross-sectional study
2023, Journal of Affective DisordersCharacteristics of blood biomarkers and eating behavior among older community-dwelling adults with typical and atypical depression
2023, Clinical Nutrition Open ScienceMacronutrient intake as a prospective predictor of depressive symptom severity: An exploratory study with adolescent elite athletes
2023, Psychology of Sport and Exercise