Elsevier

Journal of Affective Disorders

Volume 175, 1 April 2015, Pages 248-250
Journal of Affective Disorders

Research Report
Does reverse causality explain the relationship between diet and depression?

https://doi.org/10.1016/j.jad.2015.01.007Get rights and content

Abstract

Background

Observational studies have repeatedly demonstrated relationships between habitual diet quality and depression. However, whilst reverse causality has not been the identified mechanism for these associations in prospective studies, the relationship between diet and depression is likely complex and bidirectional. Thus explicit investigation of the reverse causality hypothesis is warranted.

Methods

Data were drawn from the Personality and Total Health (PATH) Through Life Study, a longitudinal community survey following three age cohorts from Australia. Analyses evaluated the relationships between past depression and treatment, current depressive symptoms and dietary patterns.

Results

Individuals with current depression had lower scores on a healthy dietary pattern; however, those who had been previously depressed and sought treatment had higher scores on the healthy dietary pattern at the later baseline assessment. Moreover, those who had reported prior, but not current, depression also had lower scores on the western dietary pattern than those without prior depression, regardless of whether they had been previously treated for their symptoms.

Limitations

Self-report data and possible recall bias limit our conclusions.

Conclusions

In this study, prior depression was associated with better quality diets at the later time point. Thus, while current depression is associated with poorer dietary habits, a history of depression may prompt healthier dietary behaviours in the long term. Given the demonstrated relationships between diet quality and depressive illness, clinicians should advocate dietary improvement for their patients with depression and should not be pessimistic about the likelihood of adherence to such recommendations.

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)

  • F.N. Jacka

    Dietary patterns and depressive symptoms over time: examining the relationships with socioeconomic position, health behaviours and cardiovascular risk

    PLoS One

    (2014)
  • F.N. Jacka

    A prospective study of diet quality and mental health in adolescents

    PLoS One

    (2011)
  • Cited by (118)

    • Global and Epidemiological Perspectives on Diet and Mood

      2024, The Gut-Brain Axis, Second Edition
    View all citing articles on Scopus
    View full text