Conjugated linoleic acid (CLA) is a class of isomers of linoleic acid, of which cis-9, trans-11 (c9, t11) and trans-10,cis-12 (t10,c12) CLA predominate. CLA is naturally present in the milk and meat of ruminants (cows and sheep). The concentrations of CLA in ruminant-derived products range from 3 to 7 mg CLA/g fat. The estimated average daily intake of CLA from these dietary sources ranges from 0.19 to 1.5 g CLA and varies for different countries (1). 

    CLA has been shown to have a variety of potential human health benefits through animal studies, including positive effects on cancer, body composition, diabetes, and cardiovascular disease. In addition, animal studies have suggested that CLAs have beneficial effects on immune function. Results from animal studies suggested that CLA may modulate the immune response under immune imbalance situations, such as allergies (1).

    The effects of the natural CLA isomer, cis-9, trans- 11-CLA on allergy symptoms and immunological parameters were conducted in human subjects with birch pollen allergy. In this randomized, placebo-controlled study, forty subjects (20–46 years) with diagnosed birch pollen allergy received 2 g CLA/d in capsules, which contained 65·3% cis-9, trans-11-CLA, and 8·5% trans-10, cis-12-CLA (n= 20), or placebo (high-oleic acid sunflower-seed oil) (n=20) for 12 weeks (2).

 

    The supplementation began 8 weeks before the birch pollen season and continued throughout the season. Allergy symptoms and use of medication were recorded daily. Lymphocyte subsets, cytokine production, immunoglobulins, C-reactive protein, lipid and glucose metabolism, and lipid peroxidation were assessed before and after supplementation (2).

     The CLA group reported a better overall feeling of well-being (p<0·05) and less sneezing (p<0·05) during the pollen season. CLA supplementation decreased the in vitro production of TNF-a (p<0·01), interferon-g (p<0·05), and IL-5 (p<0·05). Total plasma IgE and birch-specific IgE concentrations did not differ between groups, whereas plasma IgA (p<0·05), granulocyte-macrophage colony-stimulating factor (p<0·05) and eosinophil-derived neurotoxin (p<0·05) concentrations were lower after CLA supplementation. Urinary excretion of 8-iso-PGF2a, a major F2-isoprostane (p< 0·01), and 15-keto-dihydro-PGF2a, a primary PGF2a metabolite (p<0·05), were increased in the CLA group. The results suggested that cis-9, trans-11-CLA had modest anti-inflammatory effects in allergic subjects (2).

    In a study of people with allergic problems, twenty-nine asthmatic children and adolescents (age 6-18 y) with diagnosed allergic sensitization against grass pollen, house dust mite, or cat hair/epithelia consumed daily a portion of yogurt containing either 3 g CLA (75 % c9,t11-CLA, 87 % purity) or placebo (safflower oil) over 12 weeks. At study start and end, lung function parameters, specific IgE, in vitro allergen-induced cytokine production in peripheral blood mononuclear cells (PBMC), plasma ECP, urinary 8-oxodG as markers of oxidation, fatty acid profiles of erythrocytes, and routine hematological parameters were determined. Before blood samplings, 3-day dietary records were requested. Throughout the study, the participants documented daily their peak expiratory flow and kept records about their allergy symptoms and usage of demand medication (3).

    In contrast to the CLA group, PBMC-produced IFN-γ and IL-4 increased significantly and by trend, respectively, in the placebo group. Plasma ECP also tended to increase in the placebo group. In the pollen subgroup, FEV1 improved upon both CLA and placebo oil supplementation. In both intervention groups, the n-6/n-3 PUFA ratio in red blood cells decreased, mainly due to an increase in n-3 PUFA. Moreover, 8-oxodG excretion increased in both groups. No changes occurred regarding specific IgE concentrations, allergy symptoms, and volume parameters. The results indicated that CLA modestly dampened the inflammatory response on the cellular level (3).

    One study investigated the effect of dietary CLA supplementation (3g/day; 50:50 mixture of the two major isomers) on the immune system and plasma lipids and glucose of healthy human volunteers. This double-blind, randomized, placebo-referenced study was conducted on 28 healthy human participants aged 25-50 years, who received either high oleic sunflower oil (placebo) or 50% CLA 9-11 and 50% CLA 10-12 CLA isomers (50:50 CLA-triglyceride form) at 3 g per day for 12 weeks. A 12-week washout period followed the intervention period (4).

    Levels of plasma IgA and IgM were increased (p < 0.05 and 0.01 respectively), while plasma IgE levels were decreased (p < 0.05). CLA supplementation also decreased the levels of the proinflammatory cytokines, TNF-alpha (20% decrease), and IL-1beta (p < 0.05), but increased the levels of the anti-inflammatory cytokine, IL-10 (p < 0.05). Another aspect of immune function, delayed-type hypersensitivity (DTH) response, was decreased during and after CLA supplementation (p < 0.05). Plasma glucose, lipids, and lymphocyte phenotypic results were not affected significantly by CLA.  IFN-gamma may contribute to chronic inflammation. A 35% decrease in IFN-gamma was observed in healthy subjects after daily supplementation with a 3 g CLA mixture (4).

    The results from these studies showed that CLA, a fatty acid naturally found in dairy and meat products, can beneficially affect immune function in healthy human volunteers and people with allergies. CLA may be beneficial for relieving allergic symptoms.

References:

1. O'Shea, M., Bassaganya-Riera, J., & Mohede, I. C. (2004). Immunomodulatory properties of conjugated linoleic acid. The American Journal of Clinical Nutrition, 79(6), 1199S-1206S. https://doi.org/10.1093/ajcn/79.6.1199S.

2. Turpeinen AM, Ylönen N, von Willebrand E, Basu S, Aro A. Immunological and metabolic effects of cis-9, trans-11-conjugated linoleic acid in subjects with birch pollen allergy. Br J Nutr. 2008 Jul;100(1):112-9. doi: 10.1017/S0007114507886326. Epub 2008 Jan 2. PMID: 18167173.

3. Jaudszus A, Mainz JG, Pittag S, Dornaus S, Dopfer C, Roth A, Jahreis G. Effects of a dietary intervention with conjugated linoleic acid on immunological and metabolic parameters in children and adolescents with allergic asthma--a placebo-controlled pilot trial. Lipids Health Dis. 2016 Feb 3;15:21. doi: 10.1186/s12944-016-0187-6. PMID: 26843092; PMCID: PMC4739392.

4. Song HJ, Grant I, Rotondo D, Mohede I, Sattar N, Heys SD, Wahle KW. Effect of CLA supplementation on immune function in young healthy volunteers. Eur J Clin Nutr. 2005 Apr;59(4):508-17. doi: 10.1038/sj.ejcn.1602102. PMID: 15674307.

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