Effects of the flavonol quercetin and α-linolenic acid on n-3 PUFA status in metabolically healthy men and women: a randomised, double-blinded, placebo-controlled, crossover trial

Double-blind, randomized, placebo-controlled, crossover trial in metabolically healthy adults aged 19–35 years (BMI 19–25 kg/m2); 74 enrolled (37 women, 37 men); 67 completed per-protocol.

Alpha-linolenic acid (ALA): 3.3 g/day for 8 weeks, delivered via rapeseed oil–based margarine (~30 g/day) and refined rapeseed oil (~25 g/day). Quercetin: 190 mg/day, three capsules daily with principal meals; duration 8 weeks.

Serum phospholipid ALA increased by 69.3% with placebo and 55.8% with quercetin; EPA increased by 37.3% (placebo) and 25.5% (quercetin). DHA decreased by 9.3% with quercetin. Erythrocyte ALA rose by 48.6% (placebo) and 45.8% (quercetin); EPA rose by 12.7% (quercetin); DHA decreased by 2.9% with both treatments; DPA increased (placebo +3.8%; quercetin +4.5%). No sex differences observed; quercetin did not enhance conversion of ALA to long-chain n-3 PUFAs. Daily ALA (~3.6 g/day intake) via rapeseed oil/margarine improved n-3 long-chain PUFA status (ALA, EPA, DPA) but not DHA.

Did not measure Δ6-desaturase activity; 8-week duration may be insufficient to raise DHA; plasma quercetin levels were low (~0.5 μmol/L), possibly explaining lack of effect; per-protocol analysis (not intention-to-treat) may bias results; potential dietary confounding from habitual diet; seven dropouts among 74 participants may limit generalizability.