Results of intervention studies on the effects of α-linolenic acid (ALA; C18 : 3n-3) on blood pressure (BP) are conflicting. Discrepancies between studies may be due to differences in study population, as subjects with increased baseline BP levels may be more responsive. Therefore, we examined specifically the effects of ALA on 24-h ambulatory blood pressure (ABP) in (pre-) hypertensive subjects. In a double-blind, randomised, placebo-controlled parallel study, fifty-nine overweight and obese adults (forty males and nineteen females) with (pre-)hypertension (mean age of 60 (sd 8) years) received daily 10 g refined cold-pressed flaxseed oil, providing 4·7 g (approximately 2 % of energy) ALA (n 29) or 10 g of high-oleic sunflower oil as control (n 30) for 12 weeks. Compliance was excellent as indicated by vial count and plasma phospholipid fatty-acid composition. Compared with control, the changes of -1·4 mmHg in mean arterial pressure (MAP; 24 h ABP) after flaxseed oil intake (95 % CI -4·8, 2·0 mmHg, P=0·40) of -1·5 mmHg in systolic BP (95 % CI -6·0, 3·0 mmHg, P=0·51) and of -1·4 mmHg in diastolic BP (95 % CI -4·2, 1·4 mmHg, P=0·31) were not statistically significant. Also, no effects were found for office BP and for MAP, systolic BP, and diastolic BP when daytime and night-time BP were analysed separately and for night-time dipping. In conclusion, high intake of ALA, about 3-5 times recommended daily intakes, for 12 weeks does not significantly affect BP in subjects with (pre-) hypertension.
Link to Full TextBr J Nutr. , 2018., Nov 5:1-9. doi: 10.1017/S0007114518003094.
Evidence suggests that EPA (20 : 5n-3) and DHA (22 : 6n-3) can lower BP at daily intakes of more than 2 g, with hypertensive individuals being more responsive. Like n-3 long-chain PUFA, ALA may lower BP. This paper describes a 12-week, double-blind, randomised parallel, placebo-controlled study to investigate the effects of ALA consumption (4·7 g/d, approximately 2% of energy intake) on 24-h ambulatory BP (ABP) in a population with high-normal BP or mild hypertension. The results found no effect on BP when compared with a high oleic acid control.
Compliance was excellent as indicated by changes in plasma phospholipid FA composition. Other studies that have examined effects of increased ALA consumption on BP have yielded conflicting results. Effects on BP were mainly found in subjects with high-normal BP or hypertension but not in non-hypertensive subjects. It can be speculated that the FA used to replace ALA intake may have influenced the results. Most of the earlier studies used linoleic acid as control for ALA. Another possible explanation for discrepant findings between studies could be the source of ALA used. In this study, ALA from purified cold-pressed flaxseed oil was used. Other studies used different sources of ALA, such as mixtures of refined vegetable oils or milled flaxseed which may include other bioactive ingredients, such as lignans, peptides, minerals and fibres. Taken together, there is no obvious reason that can explain why in this study, unlike in some earlier studies, ALA supplementation did not affect BP.