The study involved 49 patients aged 16–64 who had recurrent self-harm.
They were randomly assigned to receive 1.2g eicosapentaenoic acid plus 0.9g decosahexaenoic acid daily or placebo.
After 12 weeks, symptoms of depression had improved most in the omega-3 group, regarding both response and remission in the Beck Depression Inventory.
Among the omega-3 group only 36 per cent had any suicidal inclination, compared with 70 per cent in those taking placebo.
More patients in the omega-3 group also showed improved perception of daily stresses, with 41 per cent showing a response, compared with 7 per cent in the placebo group.
But scores for impulsivity, aggression and hostility did not differ between the groups.
Scores in the omega-3 group continued to diverge from those of the placebo group after the 12-week end point, suggesting continued improvement may occur with longer supplementation, say the researchers.
Genomic or proteomic differences in metabolic syndromes may cause the deficit.
But the researchers said further study was needed to determine whether low intake of omega-3 fatty acids was a reversible risk factor for self-harm.