Researchers found a correlation between a higher omega-6-to-omega-3 blood ratio and the occurrence of depression, as well as the occurrence of inflammation-promoting compounds in the blood, according to a small study published in the journal Psychosomatic Medicine.
Researchers from Ohio State University College of Medicine in Columbus looked at fatty acid intake, inflammation and depression levels in 43 senior citizens. Six of the participants were found to meet the criteria for major depression. These six participants had a significantly higher ratio of omega-6 to omega-3 fatty acids than the participants who were not depressed, an average of 18:1 compared with 13:1.
Among those who were depressed, a higher omega-6-to-omega-3 ratio was found to correlate with the level of depressive symptoms.
The study authors said that the average hunter-gatherer diet provides a ratio of two or three to one, compared with the modern Western ratio of 15-17:1.
Participants who were depressed also had higher blood levels of tumor necrosis factor alpha, interleukin-6 and other compounds known to cause inflammation. These compounds have been linked to arthritis, heart disease, Type 2 diabetes and other health problems. Researcher Janice K. Kiecolt-Glaser calls them "all-purpose 'nasties' for aging."
The exact nature of the relationship between inflammation, depression and fatty acid ratio is unclear. Prior studies have demonstrated that depression, in and of itself, causes inflammation, while other studies have shown that increased omega-3 intake helps prevent depression.
Omega-3 fatty acids naturally occur in foods such as flax seed oil, walnuts and fish. Omega-6 fatty acids are the kind found in the refined vegetable oils most commonly used for cooking. The spike in omega-6 intake in the West dates to the early 20th century, when refined vegetable oil use first became common.
In addition to eating foods rich in omega-3s, those wishing to achieve a healthier omega-6:omega-3 balance can also take steps to lower their omega-6 blood levels.
"If people actually had more fruits and vegetables in their diet, they probably would have less omega-6," Kiecolt-Glaser said.