The people of Japan experience one of the lowest bipolar disorder rates in the civilized world. Compared to the 4.4 percent lifetime prevalence rate of bipolar disorder in the U.S., in Japan it’s just 0.07 percent. That’s no typo — that’s a crazy large difference.

The Japanese don’t live a less stressful lifestyle than people in the U.S. In fact, in the white-collar world, the stress levels are often higher and the people often work harder. The Japanese people live on a small, crowded island and rely heavily on imports to sustain their way of life. Japanese schools are results-oriented, and students spend an enormous time engaged in study.

So what gives? How come the Japanese have such a low rate of bipolar disorder compared with other high-income, developed nations?

In a word: fish.

The Japanese diet is focused on fish and it is their main source of protein. Forbes contributor David DiSalvo delves into whether fish — and fish oil — may help ward off mental health concerns like bipolar disorder. Each Japanese person consumes about 154 pounds of fish a year:

Collectively, they consume 12% of the world’s fish, but account for only 2% of the global population. Comparatively, the average American consumes about 16 pounds of fish and shellfish annually.

The result of consuming so much fish is that the average Japanese person has far higher levels of Omega-3 fatty acids in their brains than the average American (or average anyone-else, with the possible exception of the Chinese, who annually consume closer to Japanese levels of fish).

There is a good, solid set of research studies that examine the link between brain health and Omega-3 fatty acids. While these studies can, by and large, only speak to the correlation between these two things, findings from these studies are pretty stable — and growing:

In the past decade, at least 20 studies have shown positive correlations between consuming fish oil supplements and improved mental health. In October 2008, the Archives of Psychiatric Nursing published a systematic review of omega-3 fatty acids as a treatment for bipolar disorder. After collecting data from several well-designed studies, the authors of the review concluded that there is some evidence to support the notion that fish oil can reduce symptoms of bipolar disorder.

Some evidence is a start, but not conclusive. But if you’re looking for an inexpensive and fairly easy way to potentially help your mental and brain health, adding more fish to your diet is one thing to consider. (It’s healthier for your heart too!)

Ideally, you should get your Omega-3 fatty acids naturally — from eating fish (duh). But Americans like shortcuts and seem not to like eating fish as much as beef. So the nutritional supplement industry has complied with consumer demand for fish oil supplements. So what kind of daily dose of fish oil supplement is needed?

According to the National Institutes of Health, most fish oil studies have involved the use of 300 to 3,000 mg of the essential fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).

Research suggests that DHA and EPA are only effective for bipolar disorder when they are used in combination. If you happen to be in a store that sells fish oil, read the label and check out the percentages of DHA and EPA – in theory, the higher these percentages are, the better.

Remember, the evidence isn’t at all conclusive at this stage. An increase in fish oil in a person’s diet appears to be related to positive outcomes in bipolar disorder and more generally, in mental health, in the limited research done.

But it’s one of those little things in life that you can do more of with little cost and a lot of potential benefit, so why not give it a try?

Read the full blog: The Fish Oil Debate: Great Brain Medicine, or Just an Expensive Placebo?