But investigations into the different omega-3 fats, eicosapentaenoic acid and docosapentaenoic acid, did not reveal a significant impact, they report in this week's British Journal of Cancer.
Omega-3 fatty acid intake was evaluated in 771 patients with newly diagnosed primary lung cancer using a food-frequency questionnaire. The prevalence of depression was examined using the cut-off values for the depression subscale included in the Hospital Anxiety and Depression Scale.
After adjustment for potential confounding factors, the odds ratio for depression among patients in the highest quartile of total EPA intake and DHA intake compared with patients in the lowest quartile was not significantly different.
However those with the highest intake of alpha-linolenic acid were half as likely to develop depression as those in the lowest quartile. Total omega-3 fatty acids also had a similar risk reduction (0.55).
These results suggest that total eicosapentaenoic acid and docosapentaenoic acid intake might not be associated with depression in Japanese patients with newly diagnosed lung cancer, said the researchers involved in the joint study led by the National Cancer Centre Research Centre East in Chiba, Japan.
The findings conflict with previous evidence that has linked both EPA and DHA to reduced tendency for depression.
Dr Armand Christophe at Ghent University in Belgium has shown that low levels of EPA in the blood of new mothers was associated with higher risk of postnatal depression, but found no association with DHA levels. Researchers in the Netherlands had previously linked low levels of DHA after pregnancy with depression.
The results suggest that continuing research is needed to elucidate the role dietary fats play in mental health.