Flaxseed oil side effects

FLAXSEED

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Flaxseed oil is one of the best plant sources of omega-3 fatty acids. It may improve heart, skin, gut, and brain health, though much more research is required. How might it work, and how good is the evidence? Find out here.

What Is Flaxseed Oil?

For many centuries, people used flaxseed for its laxative properties. It is also used in bakery products, and its fibers are spun to make linen .

Constituents

Flaxseed oil contains many active compounds, including :

  • Omega-3 fatty acids (alpha-linolenic acids)
  • Proteins help decrease heart disease risk factors
  • Fibers help prevent constipation
  • Phenolic compounds (lignans) help protect against cancer
  • Minerals (calcium, magnesium, and phosphorus)

Mechanisms

The alpha-linolenic acid (ALA) from flaxseed oil is converted in the body into the unsaturated fatty acids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) .

These unsaturated fatty acids are then converted to lipids (fats). The fat molecules promote eye health as well as brain and nervous system development. They also reduce the risk of high blood pressure, high cholesterol, and cancer, improve memory, and slow aging and risk of coronary disease .

Eating flaxseed in both ground and oil forms increase blood ALA. However, consuming flaxseed oil rather than ground flaxseed results in significantly higher ALA levels in the blood .

Potential Health Benefits (Possibly Effective)

The potential benefits discussed in this section have at least one human trial to back them up, but either the results haven’t been repeated or the evidence has been contradictory. Much more research is required to determine whether flaxseed oil is effective for any of these purposes, and better alternatives are available.

It’s important to note that the FDA has not approved any flaxseed product for any medical purpose or health claim. Flaxseed is a safe component of many foods, but we still recommend talking to your doctor before using it as a supplement.

1) Heart

In a study of 56 participants, a 3-gram daily supplementation of ALA (from flaxseed oil supplements) increased blood EPA levels. These levels grew 60% after 12 weeks in comparison to the placebo group, which showed no EPA increase .

In the human body, ALA from flaxseed oil is partially metabolized into EPA and DHA. The FDA has recently approved health claims that omega-3 fatty acids (EPA and DHA specifically) may reduce the risk of high blood pressure and heart disease .

Cholesterol

In a review of 28 studies, the authors suggested that flaxseed oil slightly lowers the amount of total and LDL (bad) cholesterol in the blood. However, the amplitude of the effect was dependent on the sex and health status of participants .

12 months of high flaxseed diets also lowered LDL and total cholesterol in 110 heart disease patients. However, the degree to which flaxseed’s oil was responsible is unclear .

In hamsters, flaxseed, but not flaxseed oil, prevented cholesterol increases, casting some doubt on whether the oil alone could be useful .

The best results for cholesterol in both animals and humans have been achieved with ground flaxseed or flaxseed extract, not flaxseed oil. This suggests that non-fatty flaxseed compounds (for example, its fibers) could be responsible for this potential benefit. Additional human studies will be required to clarify.

2) Skin Health

Dietary ALA deficiency is associated with dry and uncomfortable skin and poor skin quality in humans. Flaxseed oil is rich in ALA and improved skin sensitivity and hydration in a study of 13 women .

In another study of 45 women, flaxseed oil ingestion for 12 weeks reduced skin redness and roughness .

Eczema is a common skin disorder with dry, uncomfortable, and red skin. Flaxseed oil lowered saturated fatty acid levels in both horses and human skin cells, which may reduce rash areas and help clear irregular skin .

Flaxseed oil has a high ALA content, which decreased skin cell inflammation and promoted regenerative functions in a cell study .

Flaxseed also lowered skin cell inflammation and increased repair in skin cells .

3) Gut Health

Flaxseed oil is believed to help with constipation .

In a study of 50 patients, daily supplementation with 4 mL of flaxseed oil helped relieve constipation .

Flaxseed oil also relieved Irritable Bowel Syndrome (IBS) symptoms by lowering inflammation in a pilot study of 40 IBS patients .

It is currently unclear which components of flaxseed might be responsible for these effects. Further human trials are needed.

4) Brain Health

In a study of 30 healthy adults, ALA supplementation increased BDNF levels. BDNF is a vital growth factor for neurons; the authors of this study concluded that ALA is worth studying in the context of stroke recovery .

In a study of 51 bipolar disorder patients, flaxseed oil supplementation helped improve their mood .

Daily flaxseed oil consumption helped prevent diabetes-related brain dysfunction in diabetic rats. Flaxseed oil stopped oxidative stress, thus protecting brain cells .

In rats, pretreatment with flaxseed oil protected against seizures. It helped reduce convulsion time .

Flaxseed oil supplementation significantly reduced lead and nitric oxide levels in rat brains. This helps prevent free radical formation and stops oxidative damage .

As with many of the potential benefits of flaxseed oil, many more human trials are required.

Other Potential Benefits with Insufficient Evidence

5) Blood Sugar

Individuals with PCOS tend to have high insulin and glucose levels and may be at higher risk of diabetes. In a study of 60 women with PCOS, flaxseed oil supplementation had beneficial effects on insulin metabolism .

In diabetic rats, daily flaxseed oil consumption prevented diabetes-related brain dysfunction. Flaxseed oil stopped oxidative stress and improved neurotransmitter levels, thus protecting brain cells .

However, in a study of 90 prediabetic individuals, flaxseed powder had no effect on their glucose levels or insulin resistance. These mixed results indicate the need for further human studies on the various components of flaxseed (powder vs. oil vs. extract, etc.) in people with specific health conditions .

6) Inflammation

In a study of 100 patients with carpal tunnel syndrome, the patients reported an improvement in their symptoms after topical flaxseed oil application. They had reduced inflammation and pain after a month of oil application .

In rats, flaxseed oil injections under the skin helped reduce inflammation by preventing the widening of blood vessels. It also decreased inflammatory markers (histamine, bradykinin, prostaglandin E2, and leukotriene B4) .

7) ADHD

In a pilot study of 30 children with ADHD, supplementation with flaxseed oil and vitamin C improved their ADHD symptoms and increased their EPA and DHA levels. The children had improved restlessness, inattention, self-control, and impulsiveness .

8) Menopause

In a study of 140 menopausal women, flaxseed oil supplementation improved their menopause symptoms. The women reported less hot flashes and an increase in quality of life .

9) Carpal Tunnel

In a study of 100 patients with carpal tunnel (many in both hands), topical application of flaxseed oil significantly reduced reported symptoms and improved joint function .

10) Diabetic Ulcers

In a study of 60 patients with diabetic foot ulcers, 2 g of flaxseed oil per day (in addition to conventional antibiotics) improved speed and quality of healing compared to conventional treatment alone .

11) Sjogren’s Syndrome Symptoms

Sjogren’s syndrome is an immune system disorder with uncomfortable symptoms of dry eyes and a dry mouth.

Taking daily 1 or 2 g flaxseed oil supplements significantly reduced eye inflammation and helped with dry eye symptoms in a study (RCT) of 38 Sjogren’s syndrome patients. Flaxseed greatly increased eye comfort and health .

Animal Studies (Lacking Evidence)

No clinical evidence supports the use of flaxseed or flaxseed oil for any of the conditions listed in this section. Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies listed below should not be interpreted as supportive of any health benefit.

12) Bone Health

Diets deficient in ALA have been associated with increased bone resorption and osteoporosis in humans. Since flaxseed is one of the best sources of dietary ALA, some researchers have suggested that flaxseed could help maintain bone health .

In mice that consumed a diet high in flaxseed oil, the oil appeared to help maintain bone strength. It prevented bone loss caused by drug treatment for IBD .

Flaxseed oil consumption also prevented osteoporosis in mice deficient in estrogen .

13) Weight Management

Leptin is a protein that is produced by fatty tissue in the body. Low leptin signaling results in overeating. Over time, this can lead to becoming overweight or obese .

Flaxseed oil works as a natural laxative and also lowers levels of inflammation, which aids weight loss. Eating flaxseed products induced leptin production in rabbits .

The increase in leptin production helped support fat loss and reduced fat buildup in rabbits’ arteries .

14) Kidney Health

In a rat model of kidney dysfunction, both flaxseed oil and ground flaxseed supplementation helped prevent the decline in kidney function. However, the ground flaxseed was more effective at protecting against kidney injuries than the oil .

Flaxseed oil diets also helped reduce polycystic kidney damage in male and female rats, although it was more effective in female rats. A combination of flax oil and one of its antioxidants (SDG) prevented excess protein in their urine, cystic change, and inflammation in both genders. However, females also had less oxidative damage .

Additionally, high blood pressure can damage the kidneys. In rats with high blood pressure, flaxseed oil-supplemented diets helped lower blood pressure and markers of kidney damage (creatinine, blood urea nitrogen, renin, and uric acid) .

Cancer Research

Both flaxseed and flaxseed oil contain linoorbitides, a family of compounds that have possible cancer-fighting and antioxidant activities. This compound family increases the shelf-life stability of flaxseed oil in storage. It likely does the same within the human body, providing strong antioxidant properties that lower the rate of tumor cell growth .

Flaxseed oil is also a rich source of dietary lignans, which reduce breast cancer risk and lung cancer cell growth .

Alpha-linolenic acid slows the growth of cancer cells and kills cancer cells .

In mice, flaxseed oil supplementation reduced lung tumor formation and prevented breast cancer cell formation .

Though flaxseed oil contains a compound that prevents cancer, the quantity, and frequency necessary to achieve the desired blood concentration may not make it a useful therapy in cancer treatment .

Side Effects & Precautions

Higher omega-3 fatty acids levels are associated with a slightly longer bleeding time and slower clotting time. However, there are no cases of bleeding problems documented, even at high levels of omega-3 and when taken with blood-thinning medications .

When first taking flaxseed oil, some adults who took more than 6 grams per day experienced stomach and intestinal discomfort .

Additionally, some people may be allergic to flaxseed .

Flaxseed contains small quantities of cyanogenic glycosides. In typical dietary amounts, however, flaxseed will not produce enough thiocyanate (a precursor to cyanide) to be dangerous .

Gene Interactions

In a study of 60 diabetic patients with heart disease, 12 weeks of flaxseed oil supplementation increased the expression of genes related to insulin, inflammation, and fat. It increased PPAR-α levels, which helps with insulin and fat metabolism and maintains fat and glucose balance .

Meanwhile, it reduced inflammation and heart disease risk by decreasing the gene production levels of :

  • Lipoprotein(a)
  • Interleukin 1
  • TNF-α

In diabetic rats, a diet high in flaxseed oil significantly increased PPAR-α levels. This helps maintain carbohydrate and fat balances. On the other hand, it reduced SREBP-1, which reduces the rats’ fat levels .

In diabetic rats, flaxseed oil also decreased the production of the following inflammatory genes :

  • IL-6
  • INF-γ
  • MCP-1
  • NFk-B
  • TNF-α

Limitations and Caveats

Although many animal studies have been performed, there are limited human studies of flaxseed oil. Thus, it is recommended that you consult with a doctor before taking flaxseed oil supplements for their health benefits.

Do not take flaxseed oil if it is rancid or expired, as it can potentially become toxic.

Supplementing with Flaxseed Oil

Dosage

There is no safe and effective dosage of flaxseed oil for any health claim or medical condition, because no sufficiently powered clinical trial has been conducted to find one. That being said, flaxseed and its oil are considered safe for consumption as food, and clinical trials have produced positive results with few side effects.

The recommended daily amount of alpha-linolenic acid from the diet/supplementation is 1.1 – 2.2 grams per day .

However, a medical professional may recommend higher amounts in some cases. If you have a specific health concern or disorder, talk to your doctor before taking flaxseed oil .

Sources

  • Ground seeds/powder
  • Oil
  • Supplement capsules
  • Topical Gel

Flaxseed Oil vs. Fish Oil

Both flaxseed oil and fish oil are rich sources of omega-3 fatty acids. Fish oil has EPA and DHA directly to the blood and body. Flaxseed oil has ALA, which is then changed into EPA and DHA within the body .

However, for vegetarian or vegan people, flaxseed oil could be a way to meet omega-3 daily needs and receive the positive effects of omega-3 fatty acids and lignans.

Flaxseed Oil Side Effects

It’s important to be cautious when using flaxseed oil, as there are several risks and side effects. For many, the benefits of flax seeds and flaxseed oil may outweigh the risks of using the product. Use caution when adding flaxseed oil to your diet or using it as a supplement.

Lack of definitive research

There are many studies currently under way to link the use of flaxseed oil with positive health benefits, but there is no standard use of the supplement. Discuss with your doctor the benefits of flaxseed oil for your health before trying it out. You should also discuss the length of time it’s healthy to use it as well as a recommended dosage.

Quality can vary

Flaxseed oil as a dietary supplement is not regulated by the U.S. Food and Drug Administration. Therefore, the quality and contents of flaxseed oil aren’t regulated and standardized. You should use these products with caution.

Low blood sugar

The use of flax seeds or flaxseed oil may result in lowered blood sugar. You need to be careful in using these supplements if you have diabetes or any other condition that affects your blood sugar levels. You should also be cautious about consuming flaxseed oil if you use medications that alter your blood sugar levels.

Low blood pressure

Consuming flaxseed oil may lower your blood pressure. If you have a condition or take a medication that lowers your blood pressure, adding this supplement to your diet could cause complications.

Bleeding

The use of flax seeds may increase your chances of bleeding. This may be problematic if you have a health condition that causes bleeding or if you’re on certain medications that may lead to bleeding, such as blood thinners.

Hormone adjustments

Don’t take flaxseed oil or flax seeds in pregnancy or while breastfeeding. Flaxseed oil may cause complications with women who are pregnant because of its ability to affect hormones.

Allergy

There is a chance you may have an allergy to flax seeds and flaxseed oil. You should discontinue and avoid the use of flaxseed oil if you notice itching, swelling, redness, or hives when you ingest it. Vomiting and nausea may also be signs of an allergy. See a medical center immediately if your reaction to flaxseed oil causes your throat to tighten or shortness of breath. These might be signs of anaphylactic shock.

Prostate cancer

There is conflicting research about whether ALA found in flax seeds and flaxseed oil actually causes tumors from prostate cancer to be more aggressive. Flaxseed oil does not have the nutrient lignan, which has been linked to slowing tumors for prostate cancer. Additionally, the fat in flaxseed oil may not give your body what it needs if you have prostate cancer. Oncology Nutrition advises that you should discuss the use of flax seeds with your doctor and avoid the use of flaxseed oil altogether because it provides no benefit to those with prostate cancer.

Constipation and diarrhea

Flax seeds are considered to help with constipation. Flaxseed oil doesn’t contain fiber like flax seeds, however. Therefore, using flaxseed oil to relieve your bowels will not have the same effect as using flax seeds. You should consume water regularly if you use flax seeds as a supplement. You may find that flaxseed oil leads to diarrhea.

Flax Seed Oil

Flax has been used in alternative medicine as a possibly effective aid in treating type 2 diabetes, high cholesterol, and some autoimmune diseases such as systemic lupus erythematosus (SLE).

Flax has also been used to treat osteoporosis. However, research has shown that flax may not be effective in treating this condition.

Other uses not proven with research have included enlarged prostate, heart disease, constipation, high blood pressure, irritable bowel syndrome, menopausal symptoms, weight loss, diverticulitis, attention deficit-hyperactivity disorder (ADHD), cancer (prostate, breast, lung, endometrial), and others.

It is not certain whether flax is effective in treating any medical condition. Medicinal use of this product has not been approved by the FDA. Flax should not be used in place of medication prescribed for you by your doctor.

Flax is often sold as an herbal supplement. There are no regulated manufacturing standards in place for many herbal compounds and some marketed supplements have been found to be contaminated with toxic metals or other drugs. Herbal/health supplements should be purchased from a reliable source to minimize the risk of contamination.

Flax may also be used for purposes not listed in this product guide.

Follow all directions on the product label and package. Tell each of your healthcare providers about all your medical conditions, allergies, and all medicines you use.

Before using flax, talk to your healthcare provider. You may not be able to use flax if you have certain medical conditions.

Ask a doctor, pharmacist, or other healthcare provider if it is safe for you to use this product if you have:

  • a bleeding or blood-clotting disorder;
  • diabetes;
  • a gastrointestinal obstruction;
  • a hormone sensitive cancer or condition;
  • high triglyceride levels; or
  • high or low blood pressure.

Flax is considered likely unsafe to use during pregnancy.

It is not known whether flax passes into breast milk or if it could harm a nursing baby. Do not use this product without medical advice if you are breast-feeding a baby.

Do not give any herbal/health supplement to a child without medical advice.

Flaxseed Oil

Allman MA, Pena MM, Pang D. Supplementation with flaxseed oil versus sunflower seed oil in healthy young men consuming a low fat diet: effects on platelet composition and function. Eur J Clin Nutr 1995;49:169-78. View abstract.

Ascherio A, Rimm EB, Giovannucci EL, et al. Dietary fat and risk of coronary heart disease in men: cohort follow up study in the United States. BMJ 1996;313:84-90. View abstract.

Barceló-Coblijn G, Murphy EJ, Othman R, et al. Flaxseed oil and fish-oil capsule consumption alters human red blood cell n-3 fatty acid composition: a multiple-dosing trial comparing 2 sources of n-3 fatty acid. Am J Clin Nutr 2008;88:801-9. View abstract.

Barre DE, Mizier-Barre KA, Griscti O, Hafez K. High dose flaxseed oil supplementation may affect fasting blood serum glucose management in human type 2 diabetics. J Oleo Sci 2008;57:269-73. View abstract.

Bierenbaum ML, Reichstein R, Watkins TR, and et al. Reducing atherogenic risk in hyperlipemic humans with flax seed supplementation: a preliminary report. J Am Coll Nutr. 1993;12:501-504.

Bloedon LT, Szapary PO. Flaxseed and cardiovascular risk. Nutr Rev 2004;62:18-27. View abstract.

Brouwer IA, Katan MB, Zock PL. Dietary alpha-linolenic acid is associated with reduced risk of fatal coronary heart disease, but increased prostate cancer risk: a meta-analysis. J Nutr 2004;134:919-22. View abstract.

Chavarro JE, Stampfer MJ, Li H, et al. A prospective study of polyunsaturated fatty acid levels in blood and prostate cancer risk. Cancer Epidemiol Biomarkers Prev 2007;16:1364-70. View abstract.

Christensen JH, Christensen MS, Toft E, et al. Alpha-linolenic acid and heart rate variability. Nutr Metab Cardiovasc Dis 2000;10:57-61. View abstract.

Cunnane SC, Hamadeh MJ, Liede AC, et al. Nutritional attributes of traditional flaxseed in healthy young adults. Am J Clin Nutr 1995;61:62-8. View abstract.

de Deckere EAM, Korver O, Verschuren PM, Katan MB. Health aspects of fish and n-3 polyunsaturated fatty acids from plant and marine origin. Eur J Clin Nutr 1998;52:749-53. View abstract.

de Lorgeril M, Renaud S, Mamelle N, et al. Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease. Lancet 1994;343:1454-9. View abstract.

De Stefani E, Deneo-Pellegrini H, Boffetta P, et al. Alpha-linolenic acid and risk of prostate cancer: a case-control study in Uruguay. Cancer Epidemiol Biomarkers Prev 2000;9:335-8. View abstract.

Din JN, Newby DE, Flapan AD. Omega 3 fatty acids and cardiovascular disease–fishing for a natural treatment. BMJ 2004;328:30-5. View abstract.

Djousse L, Arnett DK, Carr JJ, et al. Dietary linolenic acid is inversely associated with calcified atherosclerotic plaque in the coronary arteries: the National Heart, Lung, and Blood Institute Family Heart Study. Circulation 2005;111:2921-6. View abstract.

Djousse L, Arnett DK, Pankow JS, et al. Dietary linolenic acid is associated with a lower prevalence of hypertension in the NHLBI Family Heart Study. Hypertension 2005;45:368-73. View abstract.

Djousse L, Rautaharju PM, Hopkins PN, et al. Dietary linolenic acid and adjusted QT and JT intervals in the National Heart, Lung, and Blood Institute Family Heart study. J Am Coll Cardiol 2005;45:1716-22. View abstract.

Finnegan YE, Howarth D, Minihane AM, et al. Plant and marine derived (n-3) polyunsaturated fatty acids do not affect blood coagulation and fibrinolytic factors in moderately hyperlipidemic humans. J Nutr 2003;133:2210-3.. View abstract.

Finnegan YE, Minihane AM, Leigh-Firbank EC, et al. Plant- and marine-derived n-3 polyunsaturated fatty acids have differential effects on fasting and postprandial blood lipid concentrations and on the susceptibility of LDL to oxidative modification in moderately hyperlipidemic subjects. Am J Clin Nutr 2003;77:783-95. View abstract.

Fischer S, Honigmann G, Hora C, et al. . Dtsch Z Verdau Stoffwechselkr 1984;44:245-51. View abstract.

Francois CA, Connor SL, Bolewicz LC, Connor WE. Supplementing lactating women with flaxseed oil does not increase docosahexaenoic acid in their milk. Am J Clin Nutr 2003;77:226-33. View abstract.

Freese R, Mutanen M. Alpha-linolenic acid and marine long-chain n-3 fatty acids differ only slightly in their effects on hemostatic factors in healthy subjects. Am J Clin Nutr 1997;66:591-8. View abstract.

Giovannucci E, Rimm EB, Colditz GA, et al. A prospective study of dietary fat and risk of prostate cancer. J Natl Cancer Inst 1993;85:1571-9. View abstract.

Harper CR, Edwards MC, Jacobson TA. Flaxseed oil supplementation does not affect plasma lipoprotein concentration or particle size in human subjects. J Nutr 2006;136:2844-8. View abstract.

Harvei S, Bjerve KS, Tretli S, et al. Prediagnostic level of fatty acids in serum phospholipids: omega-3 and omega-6 fatty acids and the risk of prostate cancer. Int J Cancer 1997;71:545-51. View abstract.

Hashempur MH, Homayouni K, Ashraf A, Salehi A, Taghizadeh M, Heydari M. Effect of Linum usitatissimum L. (linseed) oil on mild and moderate carpal tunnel syndrome: a randomized, double-blind, placebo-controlled clinical trial. Daru. 2014;22:43. View abstract.

Hooper L, Thompson RL, Harrison RA, et al. Omega 3 fatty acids for prevention and treatment of cardiovascular disease. Cochrane Database Syst Rev 2004;(4):CD003177. View abstract.

Hu FB, Stampfer MJ, Manson JE, et al. Dietary intake of alpha-linolenic acid and risk of fatal ischemic heart disease among women. Am J Clin Nutr 1999;69:890-7. View abstract.

Iso H, Sato S, Umemura U, et al. Linoleic acid, other fatty acids, and the risk of stroke. Stroke 2002;33:2086-93. View abstract.

Jones PJ, Senanayake VK, Pu S, Jenkins DJ, Connelly PW, Lamarche B, Couture P, Charest A, Baril-Gravel L, West SG, Liu X, Fleming JA, McCrea CE, Kris-Etherton PM. DHA-enriched high-oleic acid canola oil improves lipid profile and lowers predicted cardiovascular disease risk in the canola oil multicenter randomized controlled trial. Am J Clin Nutr. 2014 Jul;100(1):88-97. View abstract.

Joshi K, Lad S, Kale M, et al. Supplementation with flax oil and vitamin C improves the outcome of Attention Deficit Hyperactivity Disorder (ADHD). Prostaglandins Leukot Essent Fatty Acids 2006;74:17-21. View abstract.

Kaul N, Kreml R, Austria JA, et al. A comparison of fish oil, flaxseed oil and hempseed oil supplementation on selected parameters of cardiovascular health in healthy volunteers. J Am Coll Nutr 2008;27:51-8. View abstract.

Klein V, Chajes V, Germain E, et al. Low alpha-linolenic acid content of adipose breast tissue is associated with an increased risk of breast cancer. Eur J Cancer 2000;36:335-40. View abstract.

Kolonel LN, Nomura AM, Cooney RV. Dietary fat and prostate cancer: current status. J Natl Cancer Inst 1999;91:414-28. View abstract.

Laaksonen DE, Laukkanen JA, Niskanen L, et al. Serum linoleic and total polyunsaturated fatty acids in relation to prostate and other cancers: a population-based cohort study. Int J Cancer 2004;111:444-50.. View abstract.

Layne KS, Goh YK, Jumpsen JA, et al. Normal subjects consuming physiological levels of 18:3(n-3) and 20:5(n-3) from flaxseed or fish oils have characteristic differences in plasma lipid and lipoprotein fatty acid levels. J Nutr 1996;126:2130-40. View abstract.

Leitzmann MF, Stampfer MJ, Michaud DS, et al. Dietary intake of n-3 and n-6 fatty acids and the risk of prostate cancer. Am J Clin Nutr 2004;80:204-16. View abstract.

Lemos JR, Alencastro MG, Konrath AV, Cargnin M, Manfro RC. Flaxseed oil supplementation decreases C-reactive protein levels in chronic hemodialysis patients. Nutr Res. 2012 Dec;32(12):921-7. View abstract.

Mann J, Truswell AS, eds. Essentials of Human Nutrition. Oxford: Oxford Univ Press 1998.

Merchant AT, Curhan GC, Rimm EB, et al. Intake of n-6 and n-3 fatty acids and fish and risk of community-acquired pnemonia in US men. Am J Clin Nutr 2005;82:668-74. View abstract.

Mozaffarian D, Ascherio A, Hu FB, et al. Interplay between different polyunsaturated fatty acids and risk of coronary heart disease in men. Circulation 2005;111:157-64. View abstract.

Nestel PJ, Pomeroy SE, Sasahara T, et al. Arterial compliance in obese subjects is improved with dietary plant n-3 fatty acid from flaxseed oil despite increased LDL oxidizability. Arterioscler Thromb Vasc Biol 1997;17:1163-70. View abstract.

Nordstrom DC, Honkanen VE, Nasu Y, et al. Alpha-linolenic acid in the treatment of rheumatoid arthritis. A double-blind, placebo-controlled and randomized study: flaxseed vs. safflower seed. Rheumatol Int 1995;14:231-4. View abstract.

Pan A, Yu D, Demark-Wahnefried W, et al. Meta-analysis of the effects of flaxseed interventions on blood lipids. Am J Clin Nutr 2009;90:288-97. View abstract.

Pang D, Allman-Farinelli MA, Wong T, et al. Replacement of linoleic acid with alpha-linolenic acid does not alter blood lipids in normolipidaemic men. Br J Nutr 1998;80:163-7. View abstract.

Paschos GK, Magkos F, Panagiotakos DB, et al. Dietary supplementation with flaxseed oil lowers blood pressure in dyslipidaemic patients. Eur J Clin Nutr 2007;61:1201-6. View abstract.

Prasad K. Dietary flax seed in prevention of hypercholesterolemic atherosclerosis. Atherosclerosis 1997;132:69-76. View abstract.

Ramon JM, Bou R, Romea S, et al. Dietary fat intake and prostate cancer risk: a case-control study in Spain. Cancer Causes Control 2000;11:679-85. View abstract.

Thompson LU, Rickard SE, Orcheson LJ, Seidl MM. Flaxseed and its lignan and oil components reduce mammary tumor growth at a late stage of carcinogenesis. Carcinogenesis 1996;17:1373-6. View abstract.

University of Montreal. Pregnant Women Consuming Flaxseed Oil Have High Risk Of Premature Birth.ScienceDaily, October 29, 2008. Available at: www.sciencedaily.com/releases/2008/10/081027140817.htm (Accessed May 14, 2009).

Wojtowicz JC, Butovich I, Uchiyama E, et al. Pilot, prospective, randomized, double-masked, placebo-controlled clinical trial of an omega-3 supplement for dry eye. Cornea 2010 Oct 28. . View abstract.

Why not flaxseed oil?

There’s no mercury to worry about, and flaxseed oil does contain omega-3 fats…but not the best kind.

Updated: July 29, 2019Published: October, 2006

Troll the medical literature, and you’ll come up with study after study showing that fish and fish oil are good for us, especially for our hearts but maybe also for our moods and immune systems. Various epidemiologic investigations have found that people who eat fish regularly are less likely to have heart attacks, suffer strokes, or die from sudden cardiac arrest. The definition of “regularly” varies, but it usually means at least a couple of times a week, although eating fish even once a month has been shown to make a difference.

Fish, and especially fish oil, have also been the subject of dozens of randomized clinical trials, most involving people with existing heart conditions. In large amounts (several grams a day), fish oil has been shown to nudge various cardiac risk factors (“good” HDL cholesterol, triglycerides, blood pressure) in the right direction.

Something fishy

Getting fish oil into your diet can be difficult. Eating fish will certainly do it — if you feast on salmon, trout, mackerel, and other oily species. A three-ounce serving of those fish supplies about a gram’s worth. But you’d need to eat more than a pound of farmed catfish to get that much fish oil. Or 12 ounces of light tuna canned in water.

There’s also mercury contamination to think about. Mercury accumulates in the food chain, so some of the heaviest concentrations are found in long-lived predatory species that are also some of the most desirable from the standpoint of fish-oil consumption.

The third omega-3

The health benefits of fish oil are believed to derive principally from two omega-3 fats, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Flaxseed oil contains a third, plant-based omega-3, alpha-linolenic acid (ALA). Other foods (especially walnuts) and oils (canola and soybean, for example) contain ALA. But at about 7 grams per tablespoon, flaxseed oil is by far the richest source.

The main problem with ALA is that to have the good effects attributed to omega-3s, it must be converted by a limited supply of enzymes into EPA and DHA. As a result, only a small fraction of it has omega-3’s effects — 10%–15%, maybe less. The remaining 85%–90% gets burned up as energy or metabolized in other ways. So in terms of omega-3 “power,” a tablespoon of flaxseed oil is worth about 700 milligrams (mg) of EPA and DHA. That’s still more than the 300 mg of EPA and DHA in many 1-gram fish oil capsules, but far less than what the 7 grams listed on the label might imply.

The bottom line on flaxseed oil

Flaxseed oil will give your diet a nice little omega-3 boost in the form of alpha-linolenic acid. You might try adding flaxseed oil to your salad dressing. But flaxseed oils a backup, not a substitute, for the omega-3s in fish and fish oil because of the conversion factor. If you’re in need of omega-3s but are concerned about mercury, salmon, pollock, and catfish are all low in mercury. And canned light tuna tends to be lower in mercury than albacore (“white”) tuna.

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As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review on all articles. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.

Flax Seed Oil Side Effects

Generic Name: flax

  • Side Effects
  • Interactions
  • More

Note: This document contains side effect information about flax. Some of the dosage forms listed on this page may not apply to the brand name Flax Seed Oil.

Applies to flax: oral capsule

Warning

Follow all directions on the product label and package. Tell each of your healthcare providers about all your medical conditions, allergies, and all medicines you use.

Get emergency medical help if you have signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Although not all side effects are known, flax (the active ingredient contained in Flax Seed Oil) is thought to be likely safe for most people when taken by mouth.

Stop using flax and call your healthcare provider at once if you have:

  • any bleeding that does not stop.

Common side effects may include:

  • bloating, gas, stomach ache, constipation, diarrhea, and nausea.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.

Medical Disclaimer

More about Flax Seed Oil (flax)

  • Drug Interactions
  • Drug class: herbal products

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