Flaxseed Oil: What's Really Proven in People - Blood Pressure, Inflammation, and Metabolism

Nutrients published a review that evaluates human data on flaxseed oil using a formal grading of evidence (an adaptation of the GRADE approach adopted by the Chinese Society of Nutrition). Of the 2,148 publications found, 13 papers (meta-analyses of RCTs and individual RCTs) were included in the final assessment, and each block of outcomes was “rated” based on the strength and consistency of the evidence. The bottom line: in humans, the effects of flaxseed oil on reducing inflammatory markers, moderately lowering blood pressure, and improving insulin sensitivity have been most reliably confirmed; however, the blood lipid profile (total cholesterol, LDL, etc.) does not significantly improve. Data on waist circumference, mood, and cognitive functions are still insufficient.

Background of the study

Flaxseed oil is one of the most accessible plant sources of omega-3: it is dominated by α-linolenic acid (ALA), while the "fish" EPA and DHA are almost absent. The key feature of ALA is that in the human body it is only partially converted into long-chain omega-3: in studies in men, the conversion into EPA was estimated at about 8% (in DHA - 0-4%), in women it is higher due to the influence of estrogens (up to ≈21% in EPA and ≈9% in DHA); with high consumption of n-6 PUFA (sunflower, corn oils), this path is additionally "clogged". Hence the practical question: what effects of flaxseed oil itself have been confirmed in humans, if we rely on ALA, and not on ready-made EPA / DHA?

A number of meta-analyses and clinical studies have previously looked at the “flax package” as a whole – seeds, flour, lignans and oil – which is why the conclusions were inconsistent. Most consistently, flax (in the broad sense) was found to have a slight reduction in blood pressure, especially in people with hypertension, while the results for blood lipids varied. New data from 2023-2024 on patients with hypertension confirm that adding flax can reduce SBP and DBP by several mmHg, but the magnitude of the effect varies significantly between forms and doses. This is why a “targeted” analysis of oil as a separate form is needed.

A review in Nutrients (May 2025) addresses this gap: the authors separated studies of flaxseed oil from other forms and assessed outcome blocks (inflammation, blood pressure, insulin resistance, lipids, waist circumference, mood/cognition) using an adapted GRADE approach. The overall conclusion is that the oil has the most reliable evidence for a moderate reduction in blood pressure, a reduction in inflammatory markers, and an improvement in insulin sensitivity; however, no significant improvement in the lipid profile has been observed in human studies. At the same time, the oil increases plasma EPA levels (due to partial conversion of ALA), but this is not equivalent to the effects of direct intake of EPA/DHA from fish/algae.

And one more practical detail, important specifically for oils: ALA is a polyunsaturated acid, sensitive to oxidation. The freshness of the raw material, the refining method, storage (cold, dark containers, minimal contact with air) significantly affect the formation of aldehydes/trans-isomers and the stability of the product. Therefore, even with the proven "class effect" of flaxseed oil, the correct technology and storage conditions are an obligatory part of the real benefit and safety.

What is best confirmed?

The review assigned all four directions a level of "B" for the body of the conclusions, but with different directions of effect:

• Inflammation. Flaxseed oil reduced IL-6 and hs-CRP; the effect was shown in meta-analyses and one clinical trial. This is in favor of the anti-inflammatory effect of ALA-rich oil.
• Blood pressure. In a meta-analysis of 33 RCTs, flaxseed supplements reduced SBP by ≈3.2 mmHg and DBP by ≈2.6 mmHg; in the flaxseed oil subgroup the effect was more modest (SBP −1.04; DBP −0.54 mmHg, both p<0.001). In a meta-analysis of metabolic syndrome, the oil reduced SBP by ≈3.9 mmHg; in a separate RCT in men with dyslipidemia, 12 weeks of the oil (≈8 g ALA/day) reduced both SBP and DBP compared with safflower oil.
• Insulin resistance/insulin sensitivity. According to the evidence assessment summary table, in more than 70% of studies, oil intake was associated with increased insulin sensitivity (improved QUICKI/-HOMA, etc.).
• Blood lipids: Despite the overall class "B" for the data set, the conclusion is the opposite: no significant reduction in atherogenic lipids was found (i.e. good quality evidence that there is no effect).

What is not clear yet

The authors highlight the paucity and heterogeneity of data on waist circumference, mood and cognitive functions - it is premature to draw firm conclusions. Longer and more standardized RCTs are needed.

What is so special about flaxseed oil and what were the dosages

Flaxseed oil contains ~39-60% α-linolenic acid (ALA) with a total profile of ≈73% PUFA, ≈8% SFA, and ≈19% MUFA; the n-6:n-3 ratio is about 0.3:1, one of the best among vegetable oils. In the included studies, the oil was given for 3-24 weeks at doses of ≈1-30 g/day (or 1.0-13.7 g ALA/day), often compared with soybean, corn, sunflower, and safflower oils.

Practical conclusions

• If the goal is a couple of mmHg lowering of blood pressure and mild anti-inflammatory support, flaxseed oil has a proven but moderate effect.
• There are positive signals for improving insulin sensitivity in people with metabolic risks, but protocols and duration still need to be standardized.
• According to current data, flaxseed oil is not a tool for correcting cholesterol/LDL - in this case, diet in general, weight loss, physical activity and (if indicated) medications are preferable.

Source: Nie Y. et al. The Impact of Flaxseed (Linum usitatissimum L.) Oil Supplementation on Human Health: A Human-Centric Evidence-Graded Approach. Nutrients (25 May 2025), 17(11):1791. https://doi.org/10.3390/nu17111791