Does genetic variation in the Delta6-desaturase promoter modify the association between alpha-linolenic acid and the prevalence of metabolic syndrome?

BACKGROUND Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are associated with protection against components of the metabolic syndrome, but the role of alpha-linolenic acid (ALA), the metabolic precursor of EPA and DHA, has not been studied. The Delta(6)-desaturase enzyme converts ALA into EPA and DHA, and genetic variation in the Delta(6)-desaturase gene (FADS2) may affect this conversion. OBJECTIVES We hypothesize that high ALA is associated with a lower prevalence of the metabolic syndrome and that genetic variation in FADS2 modifies this association. DESIGN We studied 1815 Costa Rican adults. Adipose tissue ALA was used as a biomarker of intake, and metabolic syndrome was identified with the definition from the National Cholesterol Education Program, Adult Treatment Panel III. Prevalence ratios (PRs) and 95% CIs were estimated from binomial regression models, and the likelihood ratio was used to test for effect modification. RESULTS High concentrations of adipose tissue ALA were associated with lower PRs of the metabolic syndrome compared with low ALA (0.81; 95% CI: 0.66, 1.00, for the comparison between the highest and the lowest quintiles; P for trend < 0.02). Higher concentrations of adipose tissue ALA were associated with a lower PR among homozygote (0.67; 95% CI: 0.53, 0.86) and heterozygote (0.84; 95% CI: 0.72, 0.99) carriers of the FADS2 T allele, but not among homozygote carriers of the deletion variant allele (0.99; 95% CI: 0.78, 1.27; P for interaction: 0.08). CONCLUSIONS Elevated ALA concentrations in adipose tissue are associated with lower prevalence of the metabolic syndrome. A lack of association among homozygote carriers of the FADS2 deletion allele suggests that this association may be due in part to the conversion of ALA into EPA.