Overview
Flax is a food and fiber crop that came from Southern Europe and Asia. Flaxseeds are the golden yellow to reddish brown seeds of flax. These seeds contain phytoestrogens, which are similar to the hormone estrogen. The seeds also contain soluble fiber and oil. Flaxseed oil contains the essential omega-3 fatty acid alpha-linolenic acid (ALA). Flaxseed has been eaten as a food or used as a medicine since 5000 BC.
Flaxseed is used for diabetes, high cholesterol, high blood pressure, obesity, breast pain (mastalgia), and swelling (inflammation) of the kidneys in people with lupus. It is also used for many other conditions, but there is no good scientific evidence to support these other uses.
Flaxseed is a good source of dietary fiber and omega-3 fatty acids. The fiber in flaxseed is found primarily in the seed coat. Taken before a meal, flaxseed fiber seems to make people feel less hungry, so that they might eat less food. Researchers believe this fiber binds with cholesterol in the intestine and prevents it from being absorbed. Flaxseed also seems to make platelets, the blood cells involved in clotting, less sticky. Overall, flaxseed’s effects on cholesterol and blood clotting may lower the risk of “hardening of the arteries” (atherosclerosis).
Flaxseed is sometimes tried for cancer because it is broken down by the body into chemicals called “lignans.” Lignans are similar to the female hormone estrogen - so similar, in fact, that they compete with estrogen for a part in certain chemical reactions. As a result, natural estrogens seem to become less powerful in the body. Some researchers believe that lignans may be able to slow down the progress of certain breast cancers and other types of cancers that need estrogen to thrive.
For systemic lupus erythematosus (SLE), flaxseed is thought to improve kidney function by decreasing the thickness of blood, reducing cholesterol levels, and reducing swelling.
Side Effects
When taken by mouth: Flaxseed is LIKELY SAFE for most adults when taken by mouth appropriately. Adding flaxseed to the diet might increase the number of bowel movements each day. It might also cause gastrointestinal (GI) side effects such as bloating, gas, abdominal pain, constipation, diarrhea, stomachache, and nausea. Higher doses are likely to cause more GI side effects.
There is some concern that taking large amounts of flaxseed could block the intestines due to the bulk-forming laxative effects of flaxseed. Flaxseed should be taken with plenty of water to prevent this from happening.
Taking flaxseed extracts that contain lignans in concentrated form is POSSIBLY SAFE. Lignans are the chemicals in flaxseed that are thought to be responsible for many of the effects. Some clinical research shows that a specific flaxseed lignan extract (Flax Essence, Jarrow Formulas) can be safely used for up to 12 weeks. Other research shows that other flaxseed extracts can be used safely for up to 6 months.
Products that contain partially defatted flaxseed, which is flaxseed with less alpha-linolenic acid content, are available. Some men choose these products because they have heard that alpha-linolenic acid might raise their risk of getting prostate cancer. It's important to remember that the source of the alpha-linolenic acid is key. Alpha-linolenic acid from dairy and meat sources has been positively associated with prostate cancer. However, alpha-linolenic acid from plant sources, such as flaxseed, does not seem to affect prostate cancer risk. Men should not worry about getting alpha-linoleic acid from flaxseed. On the other hand, there is a concern that partially defatted flaxseed might raise triglyceride levels too much. Triglycerides are a type of blood fat.
Taking raw or unripe flaxseed by mouth is POSSIBLY UNSAFE. Flaxseed in these forms is thought to be poisonous.
When applied to the skin: Flaxseed is POSSIBLY SAFE when used in a cloth on the skin.
Special Precautions
and Warnings
Pregnancy: Taking flaxseed by mouth during pregnancy is POSSIBLY UNSAFE. Flaxseed can act like the hormone estrogen. Some healthcare providers worry that this might harm the pregnancy. But to date there is no reliable clinical evidence about the effects of flaxseed on pregnancy outcomes.
Breast-feeding: There is not enough reliable information about the safety of taking flaxseed if you are breast feeding. Stay on the safe side and avoid use.
Bleeding disorders: Flaxseed might slow clotting. This raises the concern that it could increase the risk of bleeding in people with bleeding disorders. Don't use it, if you have a bleeding disorder.
Diabetes: There is some evidence that flaxseed can lower blood sugar levels and might increase the blood sugar-lowering effects of some medicines used for diabetes. There is a concern that blood sugar could drop too low. If you have diabetes and use flaxseed, monitor your blood sugar levels closely.
Gastrointestinal (GI) obstruction: People with a bowel obstruction, a narrowed esophagus (the tube between the throat and the stomach), or an inflamed (swollen) intestine should avoid flaxseed. The high fiber content of flaxseed might make the obstruction worse.
Hormone-sensitive cancers or conditions: Because flaxseed might act somewhat like the hormone estrogen, there is some concern that flaxseed might make hormone-sensitive conditions worse. Some of these conditions include breast, uterine, and ovarian cancer; endometriosis; and uterine fibroids. However, some early laboratory and animal research suggests that flaxseed might actually oppose estrogen and might be protective against hormone-dependent cancer. Still, until more is known, avoid excessive use of flaxseed if you have a hormone-sensitive condition.
High blood pressure (hypertension): Flaxseeds might lower diastolic blood pressure. Theoretically, taking flaxseeds might cause blood pressure to become too low in individuals with high blood pressure who are taking blood pressure-lowering medication.
High triglyceride levels (hypertriglyceridemia): Partially defatted flaxseed (flaxseed with less alpha linolenic acid content) might increase triglyceride levels. If your triglyceride levels are too high, don't take flaxseed.
Low blood pressure (hypotension): Flaxseeds might lower diastolic blood pressure. Theoretically, taking flaxseeds might cause blood pressure to become too low in individuals with low blood pressure.
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