Lignans

What are lignans?

Lignans, such as enterodiol and enterolactone, are nonessential nutrients, which are chemically polyphenols formed during the fermentation–by normal large intestinal bacteria–of certain plant foods, such as flax seeds ^[1]. Lignans are phytoestrogens – plant derived substances that have mild estrogen-like activity ^[1]. Lignans are absorbed and appear in the blood and urine.

Foods High i Lignans

Flaxseed, sesame and sunflower seeds (but not their oils), whole grains (wheat, rye, oats, barley) and tea are high in lignans ^[1,8].

Flaxseed Lignans Supplements

Nonprescription (over-the-counter) flaxseed-derived supplements, such as ones containing secoisolariciresinol diglycoside, are available ^[1].

Lignans Health Benefits

Flaxseed is POSSIBLY EFFECTIVE in lowering blood cholesterol levels ^{[8,9,11,12,13,14]}.

Flaxseed is POSSIBLY INEFFECTIVE in the prevention or treatment of osteoporosis ^[3].

There is INSUFFICIENT EVIDENCE ^[1,2,3] about the effectiveness of lignan supplements or flaxseed in the prevention or treatment of atherosclerosis (artery hardening) ^[9], attention deficit-hyperactivity disorder (ADHD)  bladder inflammation (interstitial cystitis), breast pain (mastalgia), cancer (breast ^[6], colorectal, endometrial, lung, ovarian, prostate) ^[9], constipation, coronary heart disease, diabetes mellitus ^[5,10], diverticulitis, enlarged prostate (benign prostatic hyperplasia), high blood pressure ^[4,7], hot flashes in menopausal women ^[9], irritable bowel syndrome, kidney inflammation caused by systemic lupus erythematosus (SLE), metabolic syndrome and stroke, skin irritation and stomach upset, or in promoting weight loss or as antioxidant.

Lignans Safety: Toxicity, Side Effects

Supplements with flaxseed extracts are POSSIBLY SAFE ^[3]. Raw or unripe flaxseed is POSSIBLY UNSAFE.

Side effects of flaxseed, which is high in fiber, may cause abdominal bloating or loose stools ^[1,2]. Flaxseed needs to be taken with sufficient amount of water otherwise it may cause constipation or even an intestinal blockage ^[9].

Pregnancy and Breastfeeding

Taking flaxseed during pregnancy is POSSIBLY UNSAFE, because lignans in flaxseed may act as estrogens ^[3]. Not enough is known about the safety of  flaxseed during breastfeeding, so breastfeeding women should avoid it ^[3].

Flaxseed may stimulate menstruation ^[2].

Who may need to avoid flaxseed? (Flaxseed-Drug Interactions)

Individuals with the following conditions may need to avoid flaxseed ^[3]:
1. Bleeding disorders. Flaxseed might slow blood clotting and may therefore increase the risk of bleeding in people with bleeding disorders or those taking anticoagulant medications, such as aspirin, clopidogrel, dalteparin, diclofenac, heparin, ibuprofen, naproxen or warfarin.

2. Diabetes. Flaxseed may lower blood glucose levels and may therefore increase the risk of hypoglycemia in diabetic patients who take hypoglycemic drugs.3. Bowel obstruction. Flaxseed, especially when taken with insufficient amount of water, may cause or worsen the obstruction of the esophagus or bowel, for example, in Crohn’s disease.

4. Hormone-sensitive cancers or conditions. Flaxseed might worsen breast, uterine and ovarian cancer, endometriosis and uterine fibroids.

5. High triglyceride levels (hypertriglyceridemia). Partially defatted flaxseed might increase triglyceride levels.

6. Low blood pressure (hypotension): Flaxseed might lower diastolic blood pressure, especially in those who take blood pressure-lowering medications.