What is it? Overview Usage Side Effects and Warnings

What are Lignans?

Lignans are naturally occurring chemicals widespread within the plant and animal kingdoms. Several lignans—with intimidating names such as secoisolariciresinol—are considered to be phytoestrogens, plant chemicals that mimic the hormone estrogen. These are especially abundant in flaxseeds and sesame seeds. Bacteria in our intestines convert the naturally occurring phytoestrogens from flaxseed into two other lignans, enterolactone and enterodiol, which also have estrogen-like effects. In this article, the term lignansrefers to these two specific lignans as well as the phytoestrogen kind, but not to the wide variety of other lignans.

Lignans are being studied for possible use in cancer prevention, particularly breast cancer. Like other phytoestrogens (such as soy isoflavones ),...

A number of preliminary human and animal studies suggest that lignans may be helpful for cancer prevention , particularly of breast and colon cancer, as well reduction of cholesterol. Other highly preliminary research suggests that flaxseeds or lignans may decrease menopausal symptoms 1 and improve kidney function in various types of kidney disease (specifically, lupus nephritis and polycystic kidney disease). 2

Warning: Flaxseed or other treatments for kidney disease should be taken only under a doctor's supervision, due to the serious nature of these disorders.

Despite positive preliminary results in animal studies, 3 studies in humans have yielded mixed results for improving cholesterol levels . 4

Safety Issues

Women who are pregnant or breastfeeding should avoid high intake of flaxseed or purified lignans. One study found that pregnant rats who ate large amounts of flaxseed (5% or 10% of their diet), or a purified lignan present in flaxseed, gave birth to offspring with altered reproductive organs and functions, and that lignans were also transferred to the baby rats during nursing. 5 In humans, eating 25 g of flaxseed per day amounts to about 5% of the diet. 6 High intake of lignans may not be safe for women with a history of estrogen-sensitive cancer, such as breast cancer or uterine cancer. A few test tube studies suggest that certain cancer cells can be stimulated by lignans such as those present in flaxseed. 7 Other studies found that lignans inhibit cancer cell...