C-reactive protein (CRP) is a known marker of systemic inflammation and an independent risk factor for cardiovascular disease. The liver produces of CRP in response to circulating cytokines which are produced under conditions of inflammation and infection. Accumulation of white adipose tissue causes increases in CRP levels because as adiposity increases, macrophages invade the adipose tissue and cause inflammation and the release of cytokines. This may explain why obese individuals have an increased risk of cardiovascular disease. Epidemiological studies have shown an inverse relationship between CRP and consumption of fish, which may suggest that fish oils have a beneficial effect on inflammation. The marine fish oils docosahexanoic acid (DHA, C22:6 (n-3)) and eicosapentanoic acid (EPA, C20:5 (n-3)) are known to inhibit the production of pro-inflammatory eicosanoids that can lead to the development of systemic inflammation, and may inhibit the synthesis of interleukin mRNA.
To test the effects of fish oil on inflammation, researcher1 fed 17 hypertriglyceridaemic men 3.0g of DHA per day for 90 days or a placebo. Blood samples collected from the men throughout the study showed that DHA supplementation decreased the number of circulating neutrophils by 10.5%, and decreased the concentrations of CRP, interleukin-6 and granulocyte monocyte-colony stimulating factor (GM-CSF) by 15%, 23% and 21%, respectively. In addition DHA increased the concentration of the anti-inflammatory matrix metalloproteinase-2 (MMP-2) by 7%. Plasma levels of CRP and number of neutrophils were positively associated with VLDL particle size. The number of circulating neutrophils was inversely associated with the DHA and EPA levels in red blood cells, but positively associated with arachidonic acid (AA, C20:4 (n-3)) levels. These results suggest that DHA supplementation is an effective nutritional strategy to lower systemic inflammation.
The effects on inflammation began to occur by half way through the study (day 45) but were not fully seen until day 90, suggesting that the DHA requires a relatively long time to accumulate in cell membranes to have its effect. Previous studies have shown that higher amounts of DHA cause greater reductions in circulating neutrophils, which suggests that the reduction is dependent on the dose of DHA. In this study, the 3.0g dose of DHA was attained from the microalgae Crypthecodinium cohinii and would be equivalent to around 10 commercially available fish oil capsules. The capsules had no EPA in them and it may therefore be expected that the addition of EPA may increase the anti-inflammatory effects. The association of CRP and neutrophil number with VLDL size may suggest that DHA decreases de novo lipogenesis by increasing insulin sensitivity or up regulating β-oxidation.
RdB
