Daily consumption of 20-30 g whole ground flaxseed in a muffin impairs vitamin B6 status in a randomized, controlled, cross-over trial in adults with above optimal plasma LDL concentrations.

Abstract: Objectives: Flaxseed contains the vitamin B6 antagonist linatine. We aimed to determine the effect of flaxseed (0, 20 and 30g) on the following markers of B6 status: plasma homocysteine (HCY; which would increase with impaired B6 status) and aspartate aminotransferase (AST; a B6 dependent enzyme whose activity would decrease with impaired vitamin B6 status).
Methods: A multi-site, randomized, double-blind, controlled, cross-over study was conducted at the Asper Clinical Research Institute in Winnipeg (n=34) and GI Labs Inc. in Toronto (n=29). Sixty-three (32 men, 31 women) healthy non-smokers, age 30-65, BMI 18.5-40.0 kg/m2, LDL 2.6-5.0 mmol/L, not taking cholesterol or blood pressure medication completed the trial which had 3 phases, each lasting 4 weeks, separated by 4-8 weeks. During each phase, participants ate 1 muffin/day containing either 0g (control), 20g or 30g ground flax. Order of treatments was random. Plasma was collected at the start and end of each phase.
Data Analyses: Plasma HCY and AST were measured on a cobas c111 clinical chemistry analyzer. SAS (9.4) was used for analysis of covariance using Proc GLM with the following variables in the model: treatment, order of treatment, participant, baseline value, interaction between treatment and order of treatment.
Results: There was a significant (p=0.04) effect of flax on final HCY concentrations with 30g flax increasing HCY by 66% compared to 0g flax (17.3 ± 1.9 vs 10.4 ± 1.9 µmol/L). HCY with 20g flax (12.7 ± 1.9 µmol/L) was not different from the other treatments. The 30g flaxseed treatment resulted in a mean plasma HCY in the hyper-homocysteinemic range (>15 µmol/L). AST decreased significantly (p<0.0001) after 30g and 20g flax by 9-13% compared to 0g flax (20.0 ± 0.4 and 21.0 ± 0.4 vs 23.0 ± 0.4 U/L, respectively).
Conclusions: These are the first data in humans to show that consumption of ground whole flaxseed at doses below the Health Canada approved LDL cholesterol lowering health claim negatively affects B6 status causing an increase in a risk factor for cardiovascular disease.