What is it?
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.
Possibly Effective for …
- Diabetes. Taking flaxseed might improve blood sugar control in people with type 2 diabetes. Benefits seem to be greatest with whole flaxseed and when used for at least 12 weeks. Flaxseed also seems to work best in people with type 2 diabetes that is not well controlled.
- High cholesterol. Taking flaxseed by mouth seems to help reduce total cholesterol and low-density lipoprotein (LDL or “bad”) cholesterol. It seems to work the best in people with high cholesterol. It might also work for people with normal cholesterol levels. It’s unclear if taking flaxseed improves triglyceride levels. Taking flaxseed doesn’t seem to improve high-density lipoprotein (HDL or “good”) cholesterol levels.
- High blood pressure. Taking flaxseed may slightly reduce blood pressure in people with high blood pressure. But it’s unclear which form or dose of flaxseed works best.
- Breast pain (mastalgia). Eating a flaxseed muffin daily for 3 months or taking flaxseed powder daily for 2 months seems to reduce breast pain that occurs at the start of the menstrual cycle.
- Obesity. Flaxseed may help reduce body weight, body mass index (BMI), and waist size in adults who are overweight or obese. Taking at least 30 grams of flaxseed per day for at least 12 weeks seems to work best.
- Swelling (inflammation) of the kidneys in people with lupus. Taking whole or ground flaxseed by mouth seems to improve kidney function in people with SLE.
Possibly Ineffective for …
- Weak and brittle bones (osteoporosis). Research shows that consuming 40 grams of ground flaxseed daily for up to one year doesn’t improve bone density in women. Similar findings were found for older men and women who took flaxseed extract.
Insufficient Evidence to Make a Determination for …
- Enlarged prostate (benign prostatic hyperplasia or BPH). Early research shows that taking 300-600 mg of flaxseed extract daily for 4 months reduces urinary tract symptoms associated with BPH. It also seems to improve quality of life.
- Breast cancer. Early research shows that eating a muffin containing 25 grams of ground flaxseed daily for about 40 days reduces tumor cell growth in women recently diagnosed with breast cancer. It’s unclear if this effect significantly improves overall breast cancer outcomes. It’s also unclear if dietary flaxseed reduces the risk of breast cancer.
- Heart disease. People eat more flaxseed and other lignan-containing foods don’t seem to have a lower risk of heart disease. But eating flaxseed after a heart procedure called percutaneous coronary intervention (PCI) may help improve blood flow.
- Long-term kidney disease (chronic kidney disease or CKD). Hemodialysis often results in abnormal cholesterol levels and inflammation. Early research suggests that taking ground flaxseed twice daily for 8 weeks during hemodialysis reduces total and low-density lipoprotein (LDL or “bad”) cholesterol. Flaxseed also seems to reduce inflammation in people on hemodialysis.
- Colon cancer, rectal cancer. Research on the effect of flaxseed on colorectal cancer risk is inconsistent. Some research shows that consumption of lignans, which are in flaxseed, is not associated with a reduced risk of colorectal cancer. But other research suggests that it is.
- Constipation. Flaxseed is a good source of dietary fiber. Eating flaxseed in muffins or other foods seems to increase bowel movements in young adults and people with diabetes.
- Cancer of the lining of the uterus (endometrial cancer). Research suggests that blood levels of lignans, which are found in flaxseed and other foods, are not associated with endometrial cancer risk.
- Prediabetes. Early research shows that taking milled flaxseed daily doesn’t improve blood sugar levels in adults with prediabetes. But flaxseed may lower systolic blood pressure (the top number) in adults with this condition.
- A long-term disorder of the large intestines that causes stomach pain (irritable bowel syndrome or IBS). Early research shows that taking 24 grams of whole or ground flaxseed daily for 4 weeks doesn’t improve quality of life or the severity of symptoms in people with IBS.
- Lung cancer. People who eat more phytoestrogens, such as those found in flaxseed, might have a lower risk of lung cancer than those who eat less.
- Symptoms of menopause. It’s unclear if flaxseed help reduce symptoms of menopause such as hot flashes. Some research shows that taking flaxseed extract for 6 months reduces symptoms and hot flashes in postmenopausal women. Other research shows that eating ground flaxseed reduces menopausal symptoms similarly to hormone therapy. But other studies show that it doesn’t work any better than taking a sugar pill. The difference in benefit might be due to the dose of flaxseed used.
- A grouping of symptoms that increase the risk of diabetes, heart disease, and stroke (metabolic syndrome). It’s unclear if flaxseed is beneficial for metabolic syndrome. Early research shows that taking flaxseed extract daily for 6 months reduces the risk of metabolic syndrome. But taking flaxseed doesn’t seem to improve markers of metabolic syndrome when used along with lifestyle modifications compared to just following lifestyle modifications.
- Build up of fat in the liver in people who drink little or no alcohol (nonalcoholic fatty liver disease or NAFLD). Early research shows that taking brown milled flaxseed daily for 12 weeks and making lifestyle changes can reduce the amount of fat and damage in the liver in adults with liver disease.
- Osteoarthritis. Early research shows that using a warm poultice containing boiled flaxseeds on the hands might help to reduce pain in people with hand osteoarthritis who are also taking their regular medications.
- Narrowing of blood vessels that causes poor blood flow to the limbs (peripheral arterial disease). Eating milled flaxseed in food doesn’t seem to prevent abnormal heart rhythm in people with peripheral arterial disease. It also doesn’t seem to help people walk farther before feeling pain. But more research is needed.
- A hormonal disorder that causes enlarged ovaries with cysts (polycystic ovary syndrome or PCOS). Early research shows that eating flaxseed might help make menstrual cycles more regular in people with PCOS. It also might help lower some fats in the blood.
- Prostate cancer. Early research suggests that taking ground flaxseed and following a low-fat diet lowers prostate-specific antigen (PSA), a marker for prostate cancer, in men who have a precancerous prostate condition. Adding flaxseed to the diet doesn’t lower PSA in men who already have prostate cancer. But it does seem to lower levels of the hormone testosterone and slow the rate at which cancer cells multiply.
- A type of inflammatory bowel disease (ulcerative colitis). Eating ground flaxseed might help to reduce the inflammation in the colon and improve symptoms in people with ulcerative colitis.
- Attention deficit-hyperactivity disorder (ADHD).
- Bladder inflammation.
- Burns and boils.
- Damage to colon from laxatives.
- Scaly, itchy skin (psoriasis).
- Stomach upset.
- Skin irritation.
- Foreign objects in the eye, when used in the eye.
- Other conditions.
More evidence is needed to rate of flaxseed for these uses.
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.
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 & 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.
Medications for diabetes (Antidiabetes drugs)
Interaction Rating=Moderate Be cautious with this combination.
Flaxseed can decrease blood sugar levels. Diabetes medications are also used to lower blood sugar. Taking flaxseed along with diabetes medications might cause your blood sugar to be too low. Monitor your blood sugar closely. The dose of your diabetes medication might need to be changed.
Some medications used for diabetes include glimepiride (Amaryl), glyburide (DiaBeta, Glynase PresTab, Micronase), insulin, pioglitazone (Actos), rosiglitazone (Avandia), chlorpropamide (Diabinese), glipizide (Glucotrol), tolbutamide (Orinase), and others.
Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)
Interaction Rating=Moderate Be cautious with this combination.
Flaxseed might slow blood clotting. Taking flaxseed along with medications that also slow clotting might increase the chances of bruising and bleeding.
Some medications that slow blood clotting include aspirin, clopidogrel (Plavix), diclofenac (Voltaren, Cataflam, others), ibuprofen (Advil, Motrin, others), naproxen (Anaprox, Naprosyn, others), dalteparin (Fragmin), enoxaparin (Lovenox), heparin, warfarin (Coumadin), and others.
Herbs and supplements that might lower blood sugar: Flaxseed might lower blood sugar. If it is taken along with other herbs and supplements that might lower blood sugar, blood sugar might become too low in some people. Some herbs and supplements that might lower blood sugar include alpha-lipoic acid, bitter melon, chromium, devil’s claw, fenugreek, garlic, guar gum, horse chestnut, Panax ginseng, psyllium, Siberian ginseng, and others.
Herbs and supplements that might slow blood clotting: Flaxseed can increase the amount of time it takes for blood to clot. Taking flaxseed along with other herbs and supplements that slow blood clotting might increase the risk of bleeding and bruising in some people. Some of these herbs include angelica, clove, danshen, garlic, ginger, ginkgo, Panax ginseng, and others.
- For diabetes: 10-60 grams of whole or ground flaxseed have been taken daily for up to 48 weeks.
- For high cholesterol: Supplements or products containing 15-40 grams of ground flaxseed have been taken daily for 1 to 3 months. Bread containing 15-50 grams of ground flaxseed have been taken daily for 4 weeks to 3 months. Muffins containing 25-40 grams of ground flaxseed or 50 grams of flaxseed meal have been taken daily for 3 weeks to one year. Also, buns, snack bars, bagels, pasta, or tea biscuits containing 30 grams of ground flaxseed have been taken daily for one year. 30 grams of a specific powdered flaxseed product (Alena, Enreco, Manitowoc, WI) have been sprinkled into foods or drinks daily for 6 months. A specific flaxseed lignan extract (BeneFlax, Archer Daniels Midland Co., Decatur, IL) has been taken daily for 6 weeks to 6 months. A 600 mg dose of another specific flaxseed lignan extract (Flax Essence, Jarrow Formulas Inc., Los Angeles, CA) has been taken three times daily for 12 weeks.
- For high blood pressure: 30 grams of milled flaxseed has been added to foods such as bagels, muffins, bars, buns, pasta, and tea biscuits taken daily for 6 months. Also, taking flaxseed powder 28-60 grams daily for up to 12 months has been used.
- For breast pain (mastalgia): 25 grams of flaxseed powder has been taken daily for 2 months. Also, a muffin containing 25 grams of flaxseed has been eaten daily for 3 months.
- For swelling (inflammation) of the kidneys in people with lupus: 15-45 grams of whole flaxseed has been taken daily in one to three divided doses for up to one year. Also, 30 grams of ground flaxseed has been taken daily for up to one year.
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