Omega-3 is a group of important fatty acids necessary for both mental and physical health. The brain and nervous system consist of 60 percent fat, and it is the long-chain fatty acids that are present in brain and nervous system. The balance between omega-3 and omega-6 is 1:1. It is therefore not surprising that a deficiency of these long-chain fatty acids can lead to disease and other health problems.

According to researcher M.A. Crawford it is very likely that the human brain evolved near the ocean, where food rich in the long-chain omega-3s were plentiful. Animals who evolved near the ocean have larger brains relative to their body weight compared to animals who did not have access to seafood. This is most likely because of the omega-3. Crawford says that the human brain capacity has now stopped increasing, and it is instead decreasing at the same time as the consumption of omega-3 is going down. If the brain does not have access to the fat it needs, it cannot function optimally. Omega-3 makes the cell membranes adaptable and flexible, which means that they can function optimally.

The fatty acid DHA has proven capable of being able to prevent aggression in times of mental stress. In a Japanese study 22 students were given a supplement with 1.5-1.8 grams DHA per day. The control group (19 students) were given a placebo with soybean oil. The study started in September at the end of the summer vacation when the students were relaxed and free from stress. It continued for three months, and ended in December, when the students had their finals in pathology and working under a lot of stress. The control group who were given placebo showed a significant increase in aggression towards others, whereas those given DHA did not show any changes in their aggression (Hamazaki et al.).

Many studies suggest that omega-3 can reduce the risk for cardiovascular disease, e.g. a study from 2002 showed that omega-3 did reduce the occurrence of cardiovascular disease. Individuals at risk for coronary heart disease can benefit from an omega-3 intake, both short-chain and long-chain omega-3. There are studies suggesting an intake of 1.5-3 grams ALA per day and 0.5-1.8 grams fish oil (DHA and EPA) per day. This is the equivalent of eating fatty fish twice per week and including rapeseed oil, walnuts and flaxseed in the diet. The authors of the study also mention that you should be aware of contamination, and you may reduce the risk by eating many different types of fish (Kris-Etherton et al.).

Most of the cardiovascular research have done on men. There is however a study where approx. 85 000 women at the age of 34 to 59 participated. This study showed similar results as studies on men, i.e. that the risk for coronary heart disease is lower for they who often eat fish and omega-3, and in particular the risk for fatal coronary heart disease was reduced (Hu et al.).

Too much omega-6 in relation to omega-3 can lead to an excess of arachidonic acid (bad eicosanoids), which contribute to increased inflammation and atherosclerosis. Omega-3 and its derivatives (good eicosanoids) dilate the blood vessels and lower the risk for blood clots. Omega-3 therefore does not only reduce risk for heart attacks, but it can also lower the blood pressure.

International Society for the Study of Fatty Acids and Lipids recommends an intake of at least 500 mg per day fish oil for good cardiovascular health.

Populations that eat plenty of fish - such as Japan and Island - have a lower frequency of breast cancer and other types of cancer, and there are many studies about this. However, there are also studies that don't show this correlation. This could be because of mistakes made in those studies, e.g. that olive oil (which have positive health effects) has been used as placebo, or that no consideration has been taken whether the fish has been farmed or wild. Garry Gordon writes more about this in the book "The Omega-3 Miracle".

Studies by Dauchy and Sauer have shown that cancer tumors grow faster if the rats are given a diet with a high amount of linoleic acid (omega-6), even faster than a diet high in saturated fat. Omega-3 had positive effects and slowed down the tumor growth.

People who eat fish have younger and healthier brains. It seems that it is the long-chain fatty acid DHA that is especially active against alzheimer. 815 healthy men and women between 65 and 94 years of age participated in a study (Morris et al.) from 1993 to 2000. During this period 131 of the participants developed alzheimer. Those who often ate fish, or at least once a week, had 60 percent less risk of developing alzheimer compared with those who rarely or never consumed fish. An intake of both DHA and EPA showed a positive effect, as well as DHA alone. However, EPA alone did not have any positive effects against alzheimer.

Individuals with cognitive impairment, dementia and alzheimer have significantly lower levels of DHA and EPA in the brain plasma (Conquer et al.). In this study 17-33 percent had lower concentrations of DHA, and 42 percent had lower concentrations of EPA compared to healthy individuals at the same age. It is likely that both EPA and DHA can have positive effects against dementia and cognitive impairment.

Joseph Hibbeln at the National Institute of Health, who is an expert on fish oil, thinks that it is the poor balance between omega-3 and omega-6, that has lead to an increase of depression and other mental problems. The consumption of omega-6 has drastically increased during the past century. There is evidence that low levels of omega-3 is related to low levels of serotonin (a feel-good substance). Depressed individuals often have low levels of serotonin.

In countries where the fish consumption is high the number of people with depression is low. Hibbeln writes that New Zealand, where the fish consumption is very low, also has the highest suicide frequency at 5.8 percent per year. In Japan, where fish consumption is almost four times as high, the suicide frequency is only 0.12 percent. There is a relation between fish consumption and suicide also in many other countries. Hibbeln and many other experts think that the balance between omega-3 and omega-6 should be 1:1.

It is not known whether it is the DHA or the EPA in fish oil that is most effective against depression. A study with 1 767 Finnish participants (Tanskanen et al.) showed that they who consumed fish twice a week, or more, were 37 percent less likely to be depressed. The risk for suicidality was 43 percent lower. Similar results were found in a 17 year long Japanese study of 265 000 people.

Psychologist Edward Suarez at the Duke University Medical Center has found that young healty women with low cholesterol levels are more likely to feel anxiety and depression than women with normal cholesterol levels. Suarez says that young women can improve their cholesterol levels by eating fish or fish oil.

Alex Richardson at Oxford writes that there are many studies indicating that an imbalanace between the fatty acids omega-3 and omega-6 could have implications for learning and behavior. Those with dyslexia and ADHD may need more of these fatty acids than others in order for their brains to function and develop normally. It seems as though it is omega-3, and in particular EPA, that gives better results than omega-6. Richardson also says that more research is needed.

A study from Oxford from 2005 has shown that an extra intake of both omega-3 and omega-6 can help those with developmental coordination disorder (DCD). DCD is often associated with difficulties in learning and behaviour. In the study, a group of children 5-12 years old with DCD, was given a supplement with omega-3 and omega-6 for three months. They showed significant improvements in spelling, reading and behavior compared to the control group who was given placebo. When the children in the control group were also given the supplement for three months, they also showed significant improvements (Richardson, Montgomery).

It is very likely that there is a relation between schizofrenia and a deficiency of polyunsaturated fatty acids in the brain. Those who have been diagnosed with schizofrenia also have low levels of both omega-3 and omega-6 in the cell membranes, and the red blood cells only contain half as much DHA and omega-6 compared to healthy brains. In the first of two studies (Peet et al.) 45 patients on antipsychotic medication were given either DHA, EPA or placebo for three months. Researcher Malcolm Peet found that EPA was superior to DHA. During the second study, only EPA and placebo were used, and the EPA treatment showed similar positive results as the previous study. In yet another study by Peet four tests out of five with EPA showed good results on schizofrenic brains.

EPA can also be effective against reumatism since it is anti-inflammatory (Fortin et al.). Omega-3 fatty acids are liquid even at low temperatures, something that can't be bad for reumatic joints. Sardines, anchovies and other oily fish who live in the cold waters of Antarctica, survive because they have lots of omega-3 in their flesh. Omega-3 has the same effect on human joints.