Effects of safflower oil and evening primrose oil in men with a low dihomo-γ-linolenic level

Abstract

Low levels of essential polyunsaturated fatty acids of the n − 6 series are associated with coronary heart disease. Linoleic acid, but not γ-linolenic acid requires the activity of Δ 6-desaturase for its conversion to dihomo-γ-linolenic and arachidonic acid. Evening primrose oil (EPO) and safflower oil (SO) are rich in linoleic acid, but EPO contains also 9% γ-linolenic acid. The effect of EPO (10, 20 and 30 ml/day) and SO (20 ml/day) for 4 months on the deposition of linoleic acid metabolites in adipose tissue of 4 groups of 6–9 men with low adipose dihomo-γ-linolenic acid was examined. EPO but not SO increased adipose dihomo-γy-linolenic acid level from 0.080 ± 0.005% to 0.101 ± 0.005% ( P < 0.01; 20 ml/day for 4 months). Adipose dihomo-γy-linolenic/linoleic acid ratio increased with EPO from 0.99 ± 0.16 × 10 2 to 1.13 ± 0.14 × 10 2 and fell on SO from 1.04 ± 0.10 × 102 to 0.90 ± 0.07 × 102 ( P < 0.01). Similar qualitative changes in the relative amount of dihomo-γ-linolenic acid in serum triglyceride and cholesteryl ester fractions were observed. At the dose of 20 ml/day, SO and EPO did not differ in their effect on serum cholesterol (7.13 ± 0.43 vs. 7.33 ± 0.42 mmol/l (NS)), LDL-cholesterol (5.10 ± 0.32 vs. 4.88 ± 0.46 mmol/l (NS)) nor did the 2 oils differ in their effect on HDL-cholesterol. These results suggest that linoleic acid is not readily converted to dihomo-y-linolenic acid due to a low activity of Δ 6-desaturase in these highly selected men. EPO was not an effective hypocholesterolaemic agent in this study.