Common Names: flaxseed, linseed
This fact sheet provides basic information about flaxseed and flaxseed oil—common names, what the science says, potential side effects and cautions, and resources for more information.
Flaxseed is the seed of the flax plant, which is believed to have originated in Egypt. It grows throughout Canada and Northwestern United States. Flaxseed oil comes from flaxseeds. The most common folk or traditional use of flaxseed is as a laxative; it is also used for hot flashes and breast pain. Flaxseed oil has different folk or traditional uses, including arthritis. Both flaxseed and flaxseed oil have been used for high cholesterol levels and in an effort to prevent cancer.
Whole or crushed flaxseed can be mixed with water or juice and taken by mouth. Flaxseed is also available in powder form. Flaxseed oil is available in liquid and capsule forms. Flaxseed contains lignans (phytoestrogens, or plant estrogens), while flaxseed oil preparations lack lignans.
What the Science Says
- Flaxseed contains soluble fiber, like that found in oat bran, and may have a laxative effect.
- Studies of flaxseed preparations to lower cholesterol levels report mixed results. A 2009 review of the clinical research found that cholesterol-lowering effects were more apparent in postmenopausal women and in people with high initial cholesterol concentrations.
- Some studies suggest that alpha-linolenic acid (a substance found in flaxseed and flaxseed oil) may benefit people with heart disease. But not enough reliable data are available to determine whether flaxseed is effective for heart conditions.
- Study results are mixed on whether flaxseed decreases hot flashes.
- Although some population studies suggest that flaxseed might reduce the risk of certain cancers, there is not enough research to support a recommendation for this use.
- NCCIH is funding studies on flaxseed. Recent studies are looking at its potential role in preventing or treating atherosclerosis (hardening of the arteries), breast cancer, and ovarian cysts.
Side Effects and Cautions
- Flaxseed and flaxseed oil supplements seem to be well tolerated. Few side effects have been reported.
- Flaxseed, like any supplemental fiber source, should be taken with plenty of water; otherwise, it could worsen constipation or, in rare cases, even cause intestinal blockage. Both flaxseed and flaxseed oil can cause diarrhea.
- The fiber in flaxseed may lower the body’s ability to absorb medications that are taken by mouth. Flaxseed should not be taken at the same time as any conventional oral medications or other dietary supplements.
- Tell all your health care providers about any complementary health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.
For More Information
The NCCIH Clearinghouse provides information on NCCIH and complementary and integrative health approaches, including publications and searches of Federal databases of scientific and medical literature. The Clearinghouse does not provide medical advice, treatment recommendations, or referrals to practitioners.
A service of the National Library of Medicine (NLM), PubMed® contains publication information and (in most cases) brief summaries of articles from scientific and medical journals. For guidance from NCCIH on using PubMed, see How To Find Information About Complementary Health Approaches on PubMed
Office of Dietary Supplements (ODS), National Institutes of Health (NIH)
ODS seeks to strengthen knowledge and understanding of dietary supplements by evaluating scientific information, supporting research, sharing research results, and educating the public. Its resources include publications (such as Dietary Supplements: What You Need to Know), fact sheets on a variety of specific supplement ingredients and products (such as vitamin D and multivitamin/mineral supplements), and the PubMed Dietary Supplement Subset.
NIH National Library of Medicine's MedlinePlus
- Flaxseed. In: Blumenthal M, Goldberg A, Brinckman J, eds. Herbal Medicine: Expanded Commission E Monographs. Newton, MA: Lippincott Williams & Wilkins; 2000:134–138.
- Flaxseed. Natural Medicines Comprehensive Database Web site. Accessed at www.naturaldatabase.com on July 10, 2009.
- Flaxseed and flaxseed oil (Linum usitatissimum). Natural Standard Database Web site. Accessed at www.naturalstandard.com on July 10, 2009.
- Flaxseed oil. Natural Medicines Comprehensive Database Web site. Accessed at www.naturaldatabase.com on July 10, 2009.
- Pan A, Yu D, Demark-Wahnefried W. Meta-analysis of the effects of flaxseed interventions on blood lipids. American Journal of Clinical Nutrition. 2009;90(2):288–297.
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