Flaxseed and its derivative flaxseed oil/linseed oil are rich sources of the essential fatty acid alpha-linolenic acid, which is a biologic precursor to omega-3 fatty acids such as eicosapentaenoic acid. Although omega-3 fatty acids have been associated with improved cardiovascular outcomes, evidence from human trials is mixed regarding the efficacy of flaxseed products for coronary artery disease or hyperlipidemia.
The lignan constituents of flaxseed (not flaxseed oil) possesses in vitro anti-oxidant and possible estrogen receptor agonist/antagonist properties, prompting theories of efficacy for the treatment of breast cancer. However, there is not sufficient human evidence to make a recommendation. As a source of fiber mucilage, oral flaxseed (not flaxseed oil) may possess laxative properties, although only one human trial has been conducted for this indication. In large doses, or when taken with inadequate water, flaxseed may precipitate bowel obstruction via a mass effect. The effects of flaxseed on blood glucose levels are not clear, although hyperglycemic effects have been reported in one case series.
Flaxseed oil contains only the alpha-linolenic acid component of flaxseed, and not the fiber or lignan components. Therefore, flaxseed oil may share the purported lipid-lowering properties of flaxseed, but not the proposed laxative or anti-cancer abilities.
Preliminary evidence suggests that alpha-linolenic acid may be associated with an increased risk of prostate cancer.
Alashi, alpha-linolenic acid, Barlean's Flax Oil, Barlean's Vita-Flax, brazen, common flax, eicosapentaenoic acid, flachssamen, flax, gamma-linolenic acid, Graine de Lin, leinsamen, hu-ma-esze, Linaceae, linen flax, lini semen, lino, lino usuale, linseed, linseed oil, lint bells, linum, Linum catharticum, Linum humile seeds, keten, omega-3 fatty acid, phytoestrogen, sufulsi, tesi-mosina, Type I Flaxseed/Flaxseed (51-55% alpha-linolenic acid), Type II Flaxseed/CDC-flaxseed (2-3% alpha-linolenic acid), winterlien.
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Laxative (flaxseed, not flaxseed oil)
Early studies in humans suggest that flaxseed can be used as a laxative. However, more information is needed to compare effectiveness and dosing to more commonly used agents.
Attention deficit hyperactivity disorder (ADHD)
Preliminary evidence supports the idea that deficiencies or imbalances in certain highly unsaturated fatty acids may contribute to attention deficit hyperactivity disorder (ADHD). Based on one trial, alpha linolenic acid-rich nutritional supplementation in the form of flax oil may improve symptoms of ADHD. More research is needed to confirm these results.
Breast cancer (flaxseed, not flaxseed oil)
There is a lack of information from human studies that flaxseed is effective in preventing or treating breast cancer.
Diabetes (flaxseed, not flaxseed oil)
Human studies on the effect of flaxseed on blood sugar levels report mixed results. Flaxseed cannot be recommended as a treatment for diabetes at this time.
Heart disease (flaxseed and flaxseed oil)
People who have had a heart attack are reported to benefit from diets rich in alpha-linolenic acid, which is found in flaxseed. Good studies that examine the effect of flaxseed on heart disease in humans are not available. It is unclear whether flaxseed supplementation alters the course of heart disease.
High blood pressure (flaxseed, not flaxseed oil)
In animals, diets high in flaxseed have mixed effects on blood pressure. One study in humans suggests that flaxseed might lower blood pressure. The evidence in this area is not clear, and more research is needed before a recommendation can be made.
High cholesterol or triglycerides (flaxseed and flaxseed oil)
In laboratory and animal studies, flaxseed and flaxseed oil are reported to lower blood cholesterol levels. Effects on blood triglyceride levels in animals are unclear, with increased levels in some research, and decreased levels in other research. Human studies in this area report mixed results, with decreased blood levels of total cholesterol and low-density lipoprotein ("bad cholesterol") in some studies, but no effect in other studies. Most human research has not been well-designed, and further research is needed before a recommendation can be made.
No strong evidence is available in this area, and no recommendation can be made without further research.
Kidney disease/Lupus nephritis (flaxseed, not flaxseed oil)
No strong evidence is available in this area. More research is needed before a recommendation can be made.
There is preliminary evidence from randomized controlled trials that flaxseed oil may help decrease mild menopausal symptoms. Additional research is necessary before a clear conclusion can be drawn and this remains an area of controversy. Patients should consult a doctor and pharmacist about treatment options before starting a new therapy. Overall effects on bone mineral density and lipid profiles remain unclear.
Menstrual breast pain (flaxseed, not flaxseed oil)
Early information from one study in women, the results of which have not been fully reported, suggests that flaxseed may reduce menstrual breast pain. However, further study is needed before a recommendation can be made.
Prostate cancer (flaxseed, not flaxseed oil)
There is limited high quality research of the effects of flaxseed or alpha-linolenic acid (which is in flaxseed) on the risk of developing prostate cancer. This area remains controversial as there is some data reporting possible increased risk of prostate cancer with alpha linolenic acid. Prostate cancer should be treated by a medical oncologist.