Inflammatory factors, including C-reactive protein, were lower among healthy people in Greece who ate more than 300g of fish each week, which may help explain why people who eat fish tend to have lower rates of heart disease, according to a new study.

"We observed a clear and strong inverse association between fish consumption and inflammatory markers related to coronary heart disease. Our findings were independent from known confounding factors, and seem to hold even in people with high blood pressure or diabetes. However, we found a lack of association in people with high cholesterol," said Demosthenes B. Panagiotakos, Ph.D., at Harokopio University in Athens, Greece.

The study was published in the July 5, 2005, issue of the Journal of the American College of Cardiology.

Inflammation within blood vessels is increasingly seen as a key marker of heart disease risk. Other studies have linked regular fish consumption to lower rates of disease. Thus, this study indicates a possible explanation for the observed benefits of eating fish.

The researchers, including lead author Antonis Zampelas, Ph.D., studied 1,514 men (age 18 to 87 years) and 1,528 women (age 18 to 89 years) from the Attica region of Greece. Of them, 5% of the men and 3% of the women were excluded due to a history of cardiovascular disease. The participants were part of the ongoing ATTICA study, which is looking at a variety of factors related to heart disease risk by studying healthy people who live in the region around Athens, Greece.

About nine out of 10 participants said they ate fish at least once a month. Compared to those who said they did not eat fish, the participants who ate the most fish, at least 300g per week (about 10.5oz.), had lower levels of C-reactive protein (33% lower), interleukin-6 (33% lower), tumor necrosis factor-alpha (21% lower), serum amyloid A (28% lower) and white blood cells (4% lower). All the results were statistically significant (p < 0.05). The researchers also reported significantly lower levels of markers of inflammation among people who ate between 150g and 300g of fish per week (about 5-10oz.).

The researchers also collected demographic and socioeconomic information from participants, as well as data on smoking and other behaviors, blood pressure, cholesterol and diabetes. All the associations between fish consumption and markers of inflammation remained significant after adjustment for these variables.

Panagiotakos said these results bolster recommendations that people consume more fish, particularly oily fish that have high levels of omega-3 fatty acids.

"For the general public, it could be suggested that consuming fish one or two times per week could lead to these beneficial effects found in our study. The general recommendation is to avoid frying the fish. Local small fish (like sardines) usually consumed with the bone are good sources of omega-3 fatty acids," he said.

Some guidelines caution pregnant women and others to limit consumption of certain types of fish due to concerns about mercury exposure.

Zampelas said the results suggest supplements also may be beneficial.

"We revealed that not only the fish portion, but also the amount of omega-3 fatty acids seems to play a role in the reduction of inflammatory markers levels. Therefore, we can speculate that omega-3 fatty acid intake in the level of 0.6g per day could be applicable to other populations, irrespective of the source of fish," he said.

Panagiotakos noted that, since this study was cross-sectional, it cannot prove conclusively that the fish consumption caused the lower levels of inflammatory markers. Also, this analysis focused on possible mechanisms that might explain associations between fish consumption and reduced heart disease; it did not analyze actual health outcomes.

Robert F. Wilson, M.D., at the University of Minnesota in Minneapolis, who was not connected with the study, said this study provides one more piece of evidence that eating fish regularly may reduce the risk of heart disease.

"The authors showed that Greeks who ate more fish had lower levels of inflammatory compounds in their blood. These inflammatory markers are associated with heart attacks and strokes, so a lower blood level is good. Significant reductions in these inflammatory markers occurred when people ate even small quantities of fish -- as low as several ounces per week," Wilson said.