Evidence

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.

Key to grades

A
Strong scientific evidence for this use
B
Good scientific evidence for this use
C
Unclear scientific evidence for this use
D
Fair scientific evidence against this use (it may not work)
F
Strong scientific evidence against this use (it likely does not work)

Grading rationale

Evidence gradeCondition to which grade level applies
B

Constipation

Good evidence suggests that flaxseed (not flaxseed oil) produces laxative effects. Loose stools have been seen in people taking flaxseed. Further research is needed to establish efficacy and dosing. Flaxseed in large doses, or when taken without enough water, may cause bowel obstruction.
C

Attention-deficit hyperactivity disorder (ADHD)

Early evidence suggests that low levels or imbalances in certain highly unsaturated fatty acids may contribute ADHD. ALA-rich nutritional supplementation in the form of flax oil may improve symptoms of ADHD. More research is needed to confirm these results.
C

Bipolar disorder

The effect of flaxseed oil in children with bipolar disorder has been examined. However, a significant effect was not reported. Further research is needed.
C

Breast cancer

It has been proposed that the lignan components of flaxseed may protect against hormone-sensitive cancers. Early evidence suggests that flaxseed supplementation may benefit the prevention or treatment of breast cancer. Additional research is needed in this area.
C

Breast pain

Flaxseed (not flaxseed oil) contains lignans that may alter estrogen activity. The hormonal effects of flaxseed may improve symptoms of breast pain. However, further research is needed before a conclusion may be drawn.
C

Clogged arteries

Flaxseed may improve clogged arteries or cardiovascular outcomes, based on antioxidant and lipid-lowering properties. n-3 polyunsaturated fatty acids and ALA may benefit individuals with heart disease. Diets rich in ALA, such as the Mediterranean diet, have improved outcomes in people with a previous heart attack. Additional research is needed in this area.
C

Diabetes

Flax has been studied for its effects on blood sugar, but reports are inconclusive. Further research is needed in this area.
C

Dry eye syndrome

Limited research suggests that flaxseed oil capsules daily may be useful in the treatment of dry eye syndrome. Additional research is needed in this area.
C

Enlarged prostate

A flaxseed lignan extract has been reported to improve urinary tract symptoms in people with benign prostatic hyperplasia (enlarged prostate). Additional well-designed trials are needed before a conclusion may be drawn.
C

Heart disease

Flaxseed may improve clogged arteries or cardiovascular outcomes, based on antioxidant and lipid-lowering properties. In humans, increased consumption of ALA may protect against stroke. However, evidence is mixed. Additional research is needed in this area.
C

High blood pressure

Early evidence suggests that higher levels of ALA in fat tissues may be associated with lower blood pressure. Flaxseed-supplemented diets have lowered blood pressure in human studies. However, future research is needed in this area.
C

High cholesterol

Flaxseed and flaxseed oil have been reported to have lipid-lowering properties. Multiple human studies on flax had mixed results on cholesterol. Additional research is needed in this area.
C

HIV/AIDS (weight gain)

Limited research suggests that ALA (derived from flax) with arginine and yeast RNA aided weight gain in people with HIV. Further research is needed before a conclusion may be drawn.
C

Irritable bowel

It has been suggested that flaxseed (not flaxseed oil) produces laxative effects. Loose stools have been observed in people taking flaxseed. Further research is needed to establish efficacy and dosing. In large doses, or when taken without enough water, flaxseed may cause bowel obstruction.
C

Lupus nephritis

Limited research suggests flaxseed may improve kidney function in people with lupus nephritis (inflamed kidney). Further research is needed before a conclusion may be drawn.
C

Menopausal symptoms

Early research suggests that flaxseed may improve menopausal symptoms, such as bone mineral density and cholesterol. However, the effects of flaxseed on menopausal symptoms are mixed. Additional research is needed.
C

Metabolic syndrome

Flaxseed has been studied for disorders of metabolic syndrome (high blood pressure, cholesterol, and diabetes) with mixed results. Trials on people with metabolic syndrome are also inconclusive. Further research is needed.
C

Obesity

Limited research exists on the effects of flaxseed in obese patients. Early research has lacked evidence of benefit in weight loss. Flaxseed has caused a reduction in hunger and an increase in fullness. Further research is needed.
C

Pneumonia (community acquired)

Limited data exists on flaxseed use for community-acquired pneumonia. Seeds from the plant have historically been used for upper respiratory infections. Further well-controlled trials are needed to confirm this conclusion.
C

Polycystic ovarian syndrome (hormonal disorder)

Flaxseed has been studied for several aspects of polycystic ovarian syndrome, including insulin resistance, obesity, and hormone changes, with mixed results. Further research is needed in this area.
C

Premature infants

It has been proposed that ALA may delay the timing of spontaneous delivery, but the available evidence lacks support for this use. The use of a flaxseed pillow in premature infants has also been studied.
C

Pressure ulcers

Flaxseed dressings on pressure ulcers have been studied. Future well-controlled trials are needed in this area.
C

Prostate cancer

There are conflicting reports on ALA and prostate cancer. Several studies suggest benefit while other studies have associated ALA with an increased risk of prostate cancer. Additional high quality studies are needed.
C

Skin conditions (sensitivity)

Seeds from the flax plant have historically been used for skin inflammation. Flaxseed oil has been applied to the skin as a salve or used for sore throat. Flaxseed oral supplementation has been studied in women with skin sensitivities. Further research is needed in this area.
D

Antioxidant

Flaxseed oil and its lignin have been found to possess antioxidant properties. Diets supplemented with flaxseed (not flaxseed oil) have been associated with an increase in cell damage. Additional research is needed.
D

Exercise performance enhancement

Limited research exists on the effects of flaxseed for improving resistance training. Taking flax oil lacked an effect on resistance training. Further research is needed.
D

Osteoporosis

Phytoestrogens, like flaxseed, have been studied for their effects on the prevention and treatment of osteoporosis. Several studies have lacked a significant effect of flaxseed on osteoporosis risk or bone mineral density. Further study is needed in this area.

Uses based on tradition or theory

The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Acne, acute respiratory distress syndrome (ARDS), allergic reactions, bladder inflammation, blood thinner, boils, bronchial irritation, burns (poultice), catarrh (inflammation of mucous membranes), colon cancer, common cold / upper respiratory tract infection, cough suppressant, diabetic nephropathy (kidney disease), diarrhea, diverticulitis (growths in colon), dysentery (severe diarrhea), enteritis (small intestine inflammation), expectorant, gastritis (stomach inflammation), gonorrhea, headache, infections, inflammation, inflammatory bowel disease (ulcerative colitis), kidney disorders, laxative-induced colon damage, liver protection, malaria, menstrual luteal phase disorders, multiple sclerosis, ovarian disorders, psoriasis (skin disorder), rheumatoid arthritis, skin cancer, skin infections, skin inflammation, sore throat, stomach pain, stomach upset, stroke, urinary tract infection, vaginitis (vaginal inflammation), vision improvement.

This evidence-based monograph was prepared by The Natural Standard Research Collaboration

www.naturalstandard.com