Higher blood levels of total n-6 PUFAs, as well as linoleic acid (LA), the most abundant n-6 PUFA in human blood, were linked with lower C-reactive protein (CRP), a critical biomarker of inflammation found researchers from the University of Eastern Finland, Kuopio.
The study used data from the 1984-1989 population-based Kuopio Ischaemic Heart Disease Risk Factor Study cohort involving 1287 healthy men aged 42–60 years .
The scientists also found no association between other n-6 PUFAs, such as arachidonic acid (AA), gamma-linolenic acid or dihomo-γ-linolenic acid, and CRP levels.
“Serum n-6 PUFAs were not associated with increased inflammation in men. In contrast, the main n-6 PUFA, LA had a strong inverse association with the key inflammation marker, CRP,” wrote first author Professor Jyrki Virtanen.
The findings are similar to some, but not all, previous population studies. Furthermore, earlier evidence had found an even stronger inverse correlation in women between serum LA and CRP.
Additionally, some randomised controlled trials have shown that large changes in LA intake have had little effect on blood levels of AA. In other studies, AA supplementation has not increased pro-inflammatory markers even at doses of 1.5 grams/day.
Serum LA has also been associated with a lower risk of chronic diseases in which low-grade inflammation is a significant risk factor.
Blood levels of LA are influenced by diet, with the main sources of this essential n-6 PUFA being vegetable oils, plant-based spreads, nuts and seeds.
Inflammatory theory oversimplified?
The body of evidence refuting earlier fears over the inflammatory effects of n-6 PUFAs is now substantial.
So how did the theory arise and what is the reality?
It had been suggested previously that high intakes of n-6 PUFAs might increase the risk of a number of diseases by promoting low-grade chronic inflammation.
LA is converted to AA in the body, which is a precursor to a set of molecules known as eicosanoids. N-3 PUFAs are also converted to (a different set of) eicosanoids.
N-3 PUFAs are widely acknowledged to produce anti-inflammatory eicosanoids (also known as resolvins), while n-6 PUFAs have been generally regarded to produce solely pro-inflammatory eicosanoids.
However, evidence has shown that AA is also a precursor to anti-inflammatory compounds.
“AA is indeed a precursor to eicosanoids with pro-inflammatory properties but it is also a precursor to compounds that have anti-inflammatory and pro-resolving (turning off inflammation) effects,” wrote Virtanen.
“Furthermore, in addition to AA, LA is a precursor for several other metabolites some of which (such as nitrated LA) have potent anti-inflammatory and pro-resolving properties,” he added.
"N-6 PUFA have been accused of being proinflammatory, but there is actually very little research evidence about that. The current study is not the only observational study that has found an inverse association between n-6 PUFA and inflammatory markers. There is also experimental study data that shows that even very high intakes of n-6 PUFA (higher than in typical diets) do not increase inflammation. Although in theory the n-6 PUFA could increase inflammation (e.g. by increasing the production of proinflammatory eicosanoids), in practice it doesn’t seem to be this simple," concluded Virtanen.
Source: European Journal of Clinical Nutrition
Published online, doi:10.1038/s41430-017-0009-6
“The associations of serum n-6 polyunsaturated fatty acids with serum C-reactive protein in men: the Kuopio Ischaemic Heart Disease Risk Factor Study”
Authors: Jyrki K. Virtanen, Jaakko Mursu, Sari Voutilainen and Tomi-Pekka Tuomainen