Key Findings:
The background to this paper indicates that interleukin-6 (IL-6) plays a role in arachidonic acid cascade-related inflammation through its receptor. IL-6 binds to the IL-6 receptor [either the membrane bound (mIL-6R) or the soluble receptor (sIL-6R)]. sIL-6R may be inhibited by ALA. In this middle-aged male twin cohort a 1 g higher habitual dietary ALA intake was significantly associated with an 11.0% lower plasma concentration of sIL-6R. Associations were not found between dietary ALA intake and plasma concentrations of IL-6, TNF-a, and CRP (the latter two also being pro-inflammatory). These associations have been inconsistent in various studies and further work is needed. The findings suggest sIL-6R is a novel biomarker for the cellular inflammatory response to dietary ALA. The data support the potential importance of increasing dietary ALA in the habitual diet to prevent CVD.
ABSTRACT:
Alpha-linolenic acid (ALA) is associated with a low risk of cardiovascular disease; however, the underlying mechanism is not completely known. The objective was to examine whether habitual dietary ALA intake is associated with plasma concentrations of inflammatory biomarkers after control for shared genetic and common environmental factors. We cross sectionally studied 353 middle-aged male twins. Habitual diet was assessed with the Willett food frequency questionnaire. Fasting plasma concentrations of interleukin-6 (IL-6) and its soluble receptor (sIL-6R), high-sensitivity C-reactive protein (hsCRP), and tumor necrosis factor-a (TNF-a) were measured. Linear mixed-effect regression analysis was used to partition the overall association into within and between pair associations. A 1g increment in habitual dietary ALA intake was associated with 11.0% lower concentrations of sIL-6R (P = 0.004) but not of IL-6 (P = 0.31), TNF-a (P = 0.16), or hsCRP (P = 0.36) after adjustment for energy intake, nutritional factors, known cardiovascular disease risk factors, and medications. After further control for shared genetic and common environmental factors by comparison of brothers within a twin pair, a twin with a 1-g higher ALA intake was likely to have 10.9% (95% CI: 3.7%, 17.6%; P = 0.004) lower sIL-6R concentrations than his co-twin with a low intake, whereas ALA intake was not significantly associated with plasma concentrations of IL-6, TNF-a, or hsCRP. These results were validated by using 1000 bootstrap samples. Habitual dietary ALA intake is inversely associated with plasma sIL-6R concentrations independent of shared genetic and common environmental influences. Lowering sIL-6R may be a mechanism underlying the cardioprotective properties of habitual dietary ALA. (Authors abstract)