A news item from ABC Chicago got my interest. The article states:

A spoonful of cod liver oil a day may help reduce the risk of depression by as much as 30%.

I can remember my mother forcing this horrible tasting stuff down my throat when I was a kid. I can't remember why. Probably just to improve my mood. Dan Buell tells us:

The oil is rich in Omega-3 fatty acids which are linked to various benefits.

Children's brains are said to be boosted by Omega-3s, which have also been claimed to reduce the risk of stroke, heart attack and cancer, although some studies have cast doubt on this.

As well as cod liver oil, vitamins, especially the B vitamins, could have an effect on your mood. According to the Happy Fun Fun blog:

Some vitamins that could help with depression are: Vitamin B-complex - this vitamin can help to keep us mentally and emotionally balanced. Vitamin B-complex cannot be stored in our bodies so we must have an intake of this vitamin on a daily basis. Substances such as alcohol, caffeine, nicotine and refined sugars can also destroy the B vitamins so try to reduce any intake of these substances.