Is flaxseed good for heart health?

For blood pressure, a little. A 2023 meta-analysis of 33 trials in 2427 people found flaxseed lowered systolic pressure by 3.19 mmHg, with an interval from 2.24 to 4.15, and diastolic by 2.61 mmHg. The trials disagreed with each other a great deal. For the things that matter most, heart attack, stroke and death from heart disease, there is no answer. We found no flaxseed trial that measured them.

Established. Flaxseed lowers blood pressure by a few mmHg in trials. Three meta-analyses agree on the direction, with effects from 1.81 to 4.75 mmHg systolic depending on the product and the people.

Unsettled. Whether that adds up to fewer heart attacks or strokes is untested for flaxseed itself. The only hard outcome data come from trials of plant omega-3 in general, and those found a small effect of low certainty.

What the trials found

Blood pressure

The 2023 review pooled whole seed, oil and lignan products together, and its heterogeneity was above 90 per cent. Its authors found larger drops in people with high blood pressure, at 30 g a day or more and in trials longer than 20 weeks. A 2025 meta-analysis of 18 randomized trials in people with cardiovascular risk factors found a drop of 4.75 mmHg systolic and 3.09 mmHg diastolic, again with very high heterogeneity.

The form matters. A 2016 meta-analysis of 15 trials in 1302 people found ground flaxseed powder lowered systolic pressure by 1.81 mmHg. Flaxseed oil and lignan extract did not significantly lower it.

The largest single result came from FlaxPAD, a double-blind trial in 110 Canadians with peripheral artery disease. Foods carrying 1.1 oz (30 g) of milled flaxseed a day left systolic pressure about 10 mmHg lower and diastolic about 7 mmHg lower than placebo foods after 6 months. That is far larger than the pooled reviews and comes from one high-risk group. After a year in the same trial, cardiac arrhythmias fell by 2 percent on flaxseed and rose by 12 percent on placebo. The difference did not reach significance, and walking distance did not differ between groups.

Inflammation and blood vessels

A 2024 meta-analysis of 54 randomized trials in 3000 people found flaxseed lowered C-reactive protein, a standardized difference of 0.46, and interleukin 6, but not TNF-alpha. These are standardized scores with no absolute amount behind them. In people who already had coronary artery disease, a 2024 meta-analysis of 6 trials found hs-CRP fell by 1.35 mg/L and fasting glucose by 8.35 mg/dL, while LDL, HDL and total cholesterol did not change. A 2026 network meta-analysis in people with heart disease or high blood pressure ranked flaxseed third for widening of the arteries on a standard test, a mean difference of 7.39, behind magnesium and vitamin D3. The certainty for flaxseed was low. A meta-analysis of 6 trials found a small fall in lipoprotein(a), a standardized difference of 0.22.

All of these are risk markers. A lower marker is a reason to test for fewer events, and no flaxseed trial has done that test yet.

Heart events, from plant omega-3 in general

A Cochrane review of 5 randomized trials in 19,327 people found more alpha-linolenic acid may slightly reduce cardiovascular events, a risk ratio of 0.95 with an interval from 0.83 to 1.07 that includes no effect. That was low-certainty evidence, and 500 people would need to eat more ALA for one fewer event. Arrhythmia probably fell, a risk ratio of 0.73 from 2 trials in 4912 people, moderate certainty, with 91 people needed for one fewer case. The ALA came from oils, margarine and supplements. None of these trials gave whole flaxseed.

Who should be careful

Not for everyone. People on blood thinners. The US National Center for Complementary and Integrative Health, NCCIH, says there are theoretical reasons flaxseed might interact with anticoagulant or antiplatelet drugs. No clinical cases are cited for that, and the question is one for whoever prescribes the drug.

NCCIH also says not to eat raw or unripe flaxseeds, because they may contain potentially toxic compounds. EFSA set an acute limit of 20 micrograms of cyanide per kg of body weight for cyanogenic glycosides from any food, linseed included. High-end exposures in some surveys of children went up to about 2.5 times over it, which EFSA judged unlikely to cause harm given its cautious assumptions. In pregnancy, NCCIH says flaxseed may be unsafe, though the evidence is not conclusive. Allergy is rare and can be severe: one case report describes a 42-year-old woman with facial swelling, breathlessness and hives 30 minutes after half a teaspoon of flaxseed flour.

What expert bodies say

The EU did not authorize a label claim that flaxseed oil or its alpha-linolenic acid promotes heart health, and no flaxseed claim is authorized there. A non-authorized claim means the evidence did not meet the bar when it was assessed, which is not proof that there is no effect. The NCCIH fact sheet on flaxseed makes no heart claim.

How we searched

What would change this answer

• A long randomized trial of ground flaxseed, at around 30 g a day, large enough to count heart attacks, strokes and cardiovascular deaths. We found none.
• Results from the registered trial of flax oil capsules for blood pressure, which has posted none.
• Blood pressure trials that report whole ground seed separately and explain why results vary so widely.

Nutrition facts and more on the seed itself are on the flaxseed page.

Sources

1. ev-flhh-01 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs with dose-response, search to July 2022 · n = 2427
   Meta-analysis of 33 trials (comprising 43 treatment arms) with 2427 participants revealed significant reductions in both systolic (WMD: -3.19 mmHg; 95% CI: -4.15 to -2.24, p < 0.001; I2 = 92.5%, p < 0.001) and diastolic blood pressure (WMD = -2.61 mmHg; 95% CI: -3.27, -1.94, p < 0.001; I2 = 94.1%, p < 0.001) following flaxseed supplementation.
   
   Who: adults in RCTs of flaxseed products
   Effect: SBP WMD -3.19 mmHg (95% CI -4.15 to -2.24), DBP -2.61 (-3.27 to -1.94); I2 above 90%; larger effects with >20 weeks, 30 g/d or more, BMI 25-30, hypertension
   Certainty: Very high heterogeneity; mixes whole seed, oil and lignan products.
   Food Funct, 2023 · checked 2026-10-07 · we read the abstract
2. ev-flhh-02 · Meta-analysis or systematic review · systematic review and meta-analysis of parallel RCTs, search to April 2024 · n = 18 RCTs
   Pooled analysis suggested that flaxseed supplementation can reduce systolic BP (SBP) (WMD: -4.75 mmHg, 95% CI: -7.05 to -2.44, P≤0.001; I2=93.6%) and diastolic BP (DBP) (WMD: -3.09 mmHg, 95% CI: -4.37 to -1.81, P≤0.001; I2=91.2%).
   
   Who: adults with cardiovascular disease risk factors in parallel RCTs
   Effect: SBP WMD -4.75 mmHg (95% CI -7.05 to -2.44), I2 93.6%; DBP -3.09 (-4.37 to -1.81), I2 91.2%
   Certainty: Newer than the corpus snapshot; heterogeneity very high; authors call for better RCTs.
   Journal of Cardiovascular and Thoracic Research. 2025 · checked 2026-10-07 · we read the abstract
3. ev-flhh-03 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 1302
   Reduction of SBP was significant with flaxseed powder (WMD: -1.81 mmHg, 95% CI: -2.03 to -1.59, p < 0.001) but not oil (WMD: -4.62 mmHg, 95%CI: -11.86 to 2.62, p = 0.211) and lignan extract (WMD: 0.28 mmHg, 95% CI: -3.49 to 4.04, p = 0.885).
   
   Who: adults in RCTs of flaxseed supplements
   Effect: SBP: powder WMD -1.81 mmHg (-2.03 to -1.59); oil -4.62 (-11.86 to 2.62, ns); lignan extract +0.28 (-3.49 to 4.04, ns)
   Certainty: Subgroups small; oil reduced diastolic pressure only.
   Clin Nutr, 2016 · checked 2026-10-07 · we read the abstract
4. ev-flhh-04 · Randomized controlled trial(s) · prospective double-blind placebo-controlled randomized trial · n = 110
   SBP was ≈ 10 mm Hg lower, and DBP was ≈ 7 mm Hg lower in the flaxseed group compared with placebo after 6 months.
   
   Who: patients with peripheral artery disease, Canada; 30 g milled flaxseed in foods vs placebo foods
   Effect: SBP about -10 mmHg, DBP about -7 mmHg vs placebo at 6 months; -15/-7 mmHg in those with SBP 140 or more at baseline; body weight unchanged
   Certainty: Single trial in a high-risk group; effect much larger than in meta-analyses.
   Hypertension, 2013 · checked 2026-10-07 · we read the abstract
5. ev-flhh-05 · Randomized controlled trial(s) · double-blind randomized controlled trial · n = 110
   After 1 year, the presence of cardiac arrhythmias in the flaxseed group decreased by 2% and increased by 12% in the placebo group (P > 0.05).
   
   Who: patients with peripheral artery disease, 1 year of 30 g/d milled flaxseed vs placebo
   Effect: arrhythmia prevalence -2% flaxseed vs +12% placebo, P > 0.05; ECG intervals unchanged; claudication distance not different between groups
   Certainty: Underpowered for arrhythmia; trend only.
   Can J Physiol Pharmacol, 2019 · checked 2026-10-07 · we read the abstract
6. ev-flhh-06 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 3000
   Overall, the flaxseed supplementation had a significant reduction in C-reactive protein (CRP) (SMD = -0.46; 95 % CI: -0.70, -0.23, P < 0.001; I2 = 82.9 %, P < 0.001), and interleukin 6 (IL-6) (SMD = -0.64, 95 % CI: -1.13, -0.16, P = 0.010; I2 = 92.7, P < 0.001).
   
   Who: adults in RCTs of flaxseed, 12 countries
   Effect: CRP SMD -0.46 (-0.70 to -0.23), I2 82.9%; IL-6 SMD -0.64 (-1.13 to -0.16); TNF-alpha SMD -0.17 (ns)
   Certainty: Standardized differences, no absolute mg/L; high heterogeneity; CRP is a risk marker, not an outcome.
   Prostaglandins Other Lipid Mediat, 2024 · checked 2026-10-07 · we read the abstract
7. ev-flhh-07 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs, search to June 2023 · n = 6 RCTs
   However, the circulating levels of fasting blood glucose (WMD = -8.35 mg/dL; 95% CI: -15.01, -1.69, p = .01) and hs-CRP (WMD = -1.35 mg/L; 95% CI: -1.93, -0.77, p < .01) significantly decreased after the intervention.
   
   Who: patients with coronary artery disease in RCTs
   Effect: hs-CRP WMD -1.35 mg/L (-1.93 to -0.77); FBG -8.35 mg/dL (-15.01 to -1.69); LDL, HDL, total cholesterol not changed; TG -18.39 mg/dL only after sensitivity analysis
   Certainty: Six small trials; no clinical events.
   Clin Cardiol, 2024 · checked 2026-10-07 · we read the abstract
8. ev-flhh-08 · Meta-analysis or systematic review · systematic review and network meta-analysis of RCTs · n = —
   The most substantial improvements in FMD were observed with magnesium (MD: 8.17; CoE: High), vitamin D3 (MD: 7.84; CoE: High), flaxseed (MD: 7.39; CoE: Low), barberry (MD: 6.64; CoE: Moderate), folic acid (MD: 3.36; CoE: Low), and omega-3 (MD: 1.83; CoE: Very low).
   
   Who: individuals with cardiovascular diseases and hypertension in RCTs of dietary interventions
   Effect: FMD MD: magnesium 8.17 (high CoE), vitamin D3 7.84 (high), flaxseed 7.39 (low), barberry 6.64, folic acid 3.36, omega-3 1.83
   Certainty: Low certainty for flaxseed; number of flaxseed trials not stated in the abstract.
   Curr Atheroscler Rep, 2026 · checked 2026-10-07 · we read the abstract
9. ev-flhh-09 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 6 RCTs
   Of the 48 RCTs, 6 were eligible for inclusion, and the results suggested a significant decrease in plasma Lp(a) levels
   
   Who: adults in RCTs of flaxseed products reporting Lp(a)
   Effect: Lp(a) SMD -0.22 (95% CI -0.41 to -0.04)
   Certainty: Small standardized effect; 6 of 48 screened RCTs eligible.
   Altern Ther Health Med, 2021 · checked 2026-10-07 · we read the abstract
10. ev-flhh-10 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of RCTs · n = 19327
    However, increased ALA may slightly reduce risk of cardiovascular disease events (NNTB 500, RR 0.95, 95% CI 0.83 to 1.07; but RR 0.91, 95% CI 0.79 to 1.04 in RCTs at low summary risk of bias; 19,327 participants; 884 cardiovascular disease events in 5 RCTs; low-certainty evidence), and probably slightly reduces risk of arrhythmia (NNTB 91, RR 0.73, 95% CI 0.55 to 0.97; 4912 participants; 173 events in 2 RCTs; moderate-certainty evidence).
    
    Who: adults in RCTs raising ALA intake vs usual or lower intake
    Effect: CVD events RR 0.95 (0.83 to 1.07), NNTB 500, low certainty; arrhythmia RR 0.73 (0.55 to 0.97), NNTB 91, 2 RCTs, 4912 people, moderate certainty
    Certainty: ALA from oils, margarine and supplements, not whole flaxseed; no RCT of flaxseed has measured hard cardiovascular events.
    Cochrane Database Syst Rev, 2020 · checked 2026-10-07 · we read the abstract
11. ev-flhh-11 · Position of an expert body · agency consumer fact sheet · n = —
    There are theoretical reasons to suspect that flaxseed or flaxseed oil might interact with other drugs, such as anticoagulant or antiplatelet drugs.
    
    Who: people taking anticoagulant or antiplatelet drugs
    Effect: theoretical interaction; talk with a provider
    Certainty: Theoretical; no clinical cases cited.
    NIH National Center for Complementary and Integrative Health, Flaxseed and Flaxseed Oil (updated February 2025) · checked 2026-10-07 · we read the section
12. ev-flhh-12 · Position of an expert body · agency consumer fact sheet · n = —
    Don't eat raw or unripe flaxseeds; they may contain potentially toxic compounds.
    
    Who: people eating flaxseed
    Effect: avoid raw or unripe seeds
    Certainty: Compounds not named on the page; cyanogenic glycosides per EFSA.
    NIH National Center for Complementary and Integrative Health, Flaxseed and Flaxseed Oil (updated February 2025) · checked 2026-10-07 · we read the section
13. ev-flhh-13 · Laboratory or animal data · case report · n = 1
    PATIENT CONCERNS: A 42-year-old female presenting with facial edema, dyspnea and urticaria after ingested half teaspoon of flaxseed flour 30 minutes previously.
    
    Who: 1 adult woman, Korea
    Effect: facial edema, dyspnoea and urticaria; IgE-mediated by intradermal test; no recurrence after avoidance
    Certainty: Flaxseed allergy is rare but can be severe.
    Medicine (Baltimore), 2017 · checked 2026-10-07 · we read the abstract
14. ev-flhh-14 · Position of an expert body · EU register entry · n = —
    POL-HC-7106 Flaxseed oil/alpha-linoleic acid Promotes heart health Non-authorised
    
    Who: EU food labeling
    Effect: claim non-authorized
    Certainty: Non-authorized means evidence did not meet the bar at assessment, not proof of no effect; no flaxseed claim is authorized.
    EU Register on nutrition and health claims, claim POL-HC-7106, snapshot 2026-09-21 · checked 2026-10-07 · we read the section
15. ev-flch-17 · Position of an expert body · agency consumer fact sheet · n = —
    Some studies of the use of flaxseed during pregnancy suggest it is possibly unsafe, but the evidence is not conclusive.
    
    Who: pregnant women
    Effect: possibly unsafe in pregnancy
    Certainty: Underlying studies not named on the page.
    NIH National Center for Complementary and Integrative Health, Flaxseed and Flaxseed Oil (updated February 2025) · checked 2026-10-07 · we read the section
16. ev-flch-18 · Position of an expert body · agency scientific opinion (EFSA CONTAM Panel) · n = —
    In the present opinion, the CONTAM Panel concluded that this ARfD is applicable for acute effects of CN regardless the dietary source.
    
    Who: European consumers of foods containing cyanogenic glycosides
    Effect: ARfD 20 mcg/kg bw for cyanide; mean exposures below ARfD; 95th percentile up to about 2.5-fold above in some child and adolescent surveys; chronic guidance value not derivable
    Certainty: EFSA judges the exceedance unlikely to cause harm given conservative assumptions.
    EFSA CONTAM Panel, Evaluation of the health risks related to the presence of cyanogenic glycosides in foods other than raw apricot kernels, EFSA Journal 2019;17(4):5662 · checked 2026-10-07 · we read the abstract