Brief report
Associations between cod liver oil use and symptoms of depression: The Hordaland Health Study

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Abstract

Background

Clinical trials suggest that omega-3 fatty acids improve the outcome of depression. This study aimed to evaluate the association between intake of cod liver oil, rich in omega-3 fatty acids, and high levels of symptoms of depression and anxiety in the general population.

Methods

We used data from the “The Hordaland Health Study ‘97–'99” (HUSK), a population based cross-sectional health survey from Norway including 21,835 subjects aged 40–49 and 70–74 years. Symptoms of depression and anxiety were measured by The Hospital Anxiety and Depression Scale (HADS). We used logistic regression to study associations.

Results

Among the participants, 8.9% used cod liver oil daily. A total of 3.6% had high levels of depressive symptoms. The prevalence of such depressive symptoms among the subjects who used cod liver oil daily was 2.5%, as compared to 3.8% in the rest of the population. The users of cod liver oil were significantly less likely to have depressive symptoms than non-users after adjusting for multiple possible confounding factors (odds ratio = 0.71, 95% confidence interval 0.52 to 0.97). These factors included age, gender, smoking habits, coffee consumption, alcohol consumption, physical activity, and education. In addition, we found that the prevalence of high levels of depressive symptoms decreased with increasing duration (0–12 months) of cod liver oil use (multivariate adjusted test for trend, P = 0.04). We were only able to study this latter association in a subset of the population aged 40–46 years.

Limitations

Data are cross sectional.

Conclusions

The findings indicate that regular use of cod liver oil is negatively associated with high levels of depressive symptoms in the general population.

Introduction

Depression is a common disorder with complex etiology. At any time, it affects 2% to 6% of the population in the United States (Kessler et al., 2005) and has a major impact on public health. Hence, identifying risk modifying factors for depression is an issue of high importance.

Biological marker studies have indicated that people with depression have deficits in omega-3 fatty acids (Parker et al., 2006). A few previous studies have suggested that frequent consumption of fish may reduce the risk of depression (Hibbeln, 1998, Tanskanen and Hibbeln, 2001) while others have not found this (Hakkarainen et al., 2004). The possible protective effect might be related to the omega-3 fatty acids content in fish (Smith, 1991, Hibbeln, 1998, Maes and Smith, 1998) and clinical evidence from short-term trials supports the notion that omega-3 supplementation in addition to standard pharmacological treatment improves the outcome for depression (Stoll and Severus, 1999, Nemets and Stahl, 2002, Peet and Horrobin, 2002, Su and Huang, 2003), but others have not found this (Silvers et al., 2005). This may be due to a variation in the dosage of omega-3 administered or to the content of docosahexaenoic acid (DHA) versus eicosapentaenoic acid (EPA) in the omega-3 oil which were used (Sontrop and Campbell, 2006). Cod liver oil is rich in omega-3 fatty acids and, to our knowledge, no studies have so far explored the association between regular use of cod liver oil and symptoms of depression in a community sample.

The aim of the present study was to investigate the association between the use of cod liver oil and depressive symptoms in a general population. Since anxiety is closely related to depression, anxiety symptoms were also studied.

Section snippets

Study population and questionnaire

The Hordaland Health Study ‘97–'99 (HUSK) is a cross-sectional health survey that was conducted from 1997 to 1999 and included all individuals in Hordaland County in Norway born between 1953 and 1957 (29,400 subjects). In addition, the study included 4849 subjects born between 1950 and 1951 and 4338 subjects born between 1925 and 1927, who had participated in an earlier study in the same area from 1992 to 1993 (The Hordaland Homocysteine Study). Of 25,634 recruited participants (66.4% of

Prevalence

The population characteristics in relation to cod liver oil use are given in Table 1. A total of 1947 subjects (8.9%) used cod liver oil daily, and 147 subjects reported that they had taken cod liver oil yesterday, but without daily use. These subjects were included in the reference group.

Association between use of cod liver oil and depression

Daily cod liver oil users were less likely to have high levels of symptoms of depression or high levels of symptoms of combined depression and anxiety, as compared to non-users (Table 2). The association

Discussion

In this large population based cross-sectional study we found that daily use of cod liver oil was negatively associated with high levels of depressive symptoms and that the prevalence of such depressive symptoms decreased with the duration of cod liver oil use after adjusting for multiple covariates. Excluding users of lithium or antidepressants did not change the association between cod liver oil use and high levels of symptoms of depression.

The large sample size and the use of a general

Acknowledgments

The data collection was conducted as part of HUSK (The Hordaland Health Study ‘97–'99) in collaboration with the Norwegian National Health Screening Service. We thank Dr. Alv A. Dahl, M.D., Ph.D., University of Oslo, Norway, for allowing us to use The Hospital Anxiety and Depression Scale (HADS) data collected in The Hordaland Health Study. The present study has been supported by research grants from Helse Vest RHF, the Research Council of Norway (“Senter for grunnleggende sykdomsmekanismer”)

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