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 flaxseed. Bacteria in our intestines convert them into two other lignans, enterolactone and enterodiol, which also have estrogen-like effects. In this article, the term "lignans" refers 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, they hook onto the same spots on cells where estrogen attaches. If there is little estrogen in the body (after menopause, for example), lignans may act like weak estrogen; but when natural estrogen is abundant in the body, lignans may instead reduce estrogen's effects by displacing it from cells. This displacement of the hormone may help prevent those cancers, such as breast cancer, that depend on estrogen to start and develop. In addition, at least one test tube study suggests that lignans may help prevent cancer in ways that are unrelated to estrogen.1
Very early evidence suggests that lignans may also be antioxidants, although the strength of their antioxidant activity is not yet clear.2,3
Besides their potential use in cancer, preliminary research suggests that lignans may have a role lowering cholesterol.4,5 In addition, weak evidence suggests a possible role for lignans in preventing atherosclerosis,6,7 treating menopausal symptoms,8 and treating chronic kidney disease.9,10
Requirements/Sources
The richest source of lignans is flaxseed (sometimes called linseed), containing more than 100 times the amount found in other foods!11Flaxseed oil, however, does not contain appreciable amounts of lignans.12 Other food sources are pumpkin seeds, whole grains, cranberries, and black or green tea.13
Therapeutic Dosages
Effective dosages of purified lignans have not been determined. In studies of flaxseed as a source of lignans, flaxseed has been taken at a dose of 5 to 38 g daily.
Cooking flaxseed apparently does not decrease the amount of lignans absorbed by the body.
Therapeutic Uses
A number of preliminary human and animal studies suggest that lignans may be helpful in cancer treatment and prevention, particularly breast and colon cancer, as well reduction of cholesterol. In addition, highly preliminary research suggests that flaxseeds or lignans may help prevent atherosclerosis,14,15 decrease menopausal symptoms16 and improve kidney function in certain types of kidney disease.17,18
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.
What Is the Scientific Evidence for Lignans?
Cancer Prevention/Treatment
The most promising use for lignans is in cancer prevention. Observational studies suggest that people who eat more lignan-containing foods have a lower incidence of breast and perhaps colon cancer;19 however, other factors may have been responsible.
Animal studies offer support for a potential cancer-preventive or even cancer-treatment effect. Several studies showed that lignan-rich foods or lignans found in flax inhibited breast and colon cancer in animals20,21,22 and reduced metastases from melanoma (a type of skin cancer) in mice.23 Test tube studies found that flaxseed or one of its lignans inhibited the growth of human breast cancer cells24 and that the lignans enterolactone and enterodiol inhibited the growth of human colon tumor cells.25
Although this preliminary research is promising, much more is needed before we can draw any conclusions. In many of these studies it isn't clear whether lignans are responsible for the benefit seen, as flaxseeds contain many other substances. Animal and human studies have begun to examine specific lignans, and results seem to confirm that at least some of the positive effects probably come from the lignans themselves;26,27,28 still, until more and better designed trials are done, we will not know lignans' precise effects on the human body, or the precise dose needed to prevent cancer.
Cholesterol and Atherosclerosis
Preliminary research in rabbits and humans suggests that lignans may help protect against atherosclerosis, a condition in which fatty deposits line arteries. Lignans may directly provide such protection, or possibly indirectly by reducing the high cholesterol that is a risk factor for atherosclerosis.
Studies in rabbits found that both flaxseed and one of its lignans, secoisolariciresinol diglucoside, were able to decrease atherosclerosis;29,30 the lignan also lowered the rabbits' cholesterol, but flaxseed by itself did not. In contrast, several human studies, two of them double-blind, found that flaxseed lowered cholesterol -- both total cholesterol and low-density lipoproteins (LDL, or"bad") cholesterol.31,32,33 However, it is entirely possible that other flaxseed components such as its fiber, oil, or proteins, rather than the lignans alone, contributed to the drop in cholesterol.34,35 Again, more research is needed to determine whether lignans themselves play a role in reducing cholesterol and atherosclerosis.
Safety Issues
Use of flaxseed as a lignan source has not been associated with any significant adverse effects other than occasional allergic reactions. However, there are some safety concerns.
Women who are pregnant or breast-feeding 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.36 In humans, eating 25 g of flaxseed per day amounts to about 5% of the diet.37
Additionally, a study of postmenopausal women found that use of flaxseed reduced estrogen levels and increased levels of prolactin.43 This suggests hormonal effects that could be problematic in pregnancy.
If you have diabetes, flaxseed (like other high-fiber foods) may delay glucose absorption.42 This may lead to better blood sugar control, but also may increase the risk of hypoglycemic reactions. Talk with your doctor about appropriate use.
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.38 Other studies found that lignans inhibit cancer cell growth.39 As with estrogen, lignans' positive or negative effects on cancer cells may depend on dose, type of cancer cell, and levels of hormones in the body. If you have a history of cancer, particularly breast cancer, talk with your doctor before consuming large amounts of flaxseeds.
Finally, flaxseeds contain tiny amounts of cyanide-containing compounds, which can be a problem for livestock eating large amounts of flax.40 Although normal cooking and baking of whole flaxseeds or flour eliminates any detectable amounts of cyanide,41 it is at least theoretically possible that eating huge amounts of raw or unprocessed flaxseeds or flaxseed meal could pose a problem. However, most authorities do not think this presents much of a risk in real life.42
As with many substances, there have been reports of life-threatening allergic reactions to flaxseed.
References
1. Sung MK, Lautens M, Thompson LU. Mammalian lignans inhibit the growth of estrogen-independent human colon tumor cells. Anticancer Res. 1998;18:1405-1408.
2. Prasad K. Hydroxyl radical-scavenging property of secoisolariciresinol diglucoside (SDG) isolated from flax-seed. Mol Cell Biochem. 1997;168:117-123.
3. Yuan YV, et al. Short-term feeding of flaxseed or its lignan has minor influence on in vivo hepatic antioxidant status in young rats. Nutr Res. 1999;19:1233-1243.
4. Jenkins DJ, Kendall CW, Vidgen E, et al. Health aspects of partially defatted flaxseed, including effects on serum lipids, oxidative measures, and ex vivo androgen and progestin activity: a controlled crossover trial. Am J Clin Nutr. 1999;69:395-402.
5. Arjmandi BH, Khan DA, Juma S, et al. Whole flaxseed consumption lowers serum LDL-cholesterol and lipoprotein(a) concentrations in postmenopausal women. Nutr Res. 1998;18:1203-1214.
6. Prasad K. Dietary flax seed in prevention of hypercholesterolemic atherosclerosis. Atherosclerosis. 1997;132:69-76.
7. Prasad K. Reduction of serum cholesterol and hypercholesterolemic atherosclerosis in rabbits by secoisolariciresinol diglucoside isolated from flaxseed. Circulation. 1999;99:1355-1362.
8. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95-120.
9. Clark WF, Parbtani A, Huff MW, et al. Flaxseed: a potential treatment for lupus nephritis. Kidney Int. 1995;48:475-480.
10. Ogborn MR, Nitschmann E, Bankovic-Calic N, et al. The effect of dietary flaxseed supplementation on organic anion and osmolyte content and excretion in rat polycystic kidney disease. Biochem Cell Biol. 1998;76;553-559.
11. Thompson LU. Experimental studies on lignans and cancer. Baillieres Clin Endocrinol Metab. 1998;12:691-705.
12. Thompson LU. Experimental studies on lignans and cancer. Baillieres Clin Endocrinol Metab. 1998;12:691-705.
13. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95-120.
14. Prasad K. Dietary flax seed in prevention of hypercholesterolemic atherosclerosis. Atherosclerosis. 1997;132:69-76.
15. Prasad K. Reduction of serum cholesterol and hypercholesterolemic atherosclerosis in rabbits by secoisolariciresinol diglucoside isolated from flaxseed. Circulation. 1999;99:1355-1362.
16. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95-120.
17. Clark WF, Parbtani A, Huff MW, et al. Flaxseed: a potential treatment for lupus nephritis. Kidney Int. 1995;48:475-480.
18. Ogborn MR, Nitschmann E, Bankovic-Calic N, et al. The effect of dietary flaxseed supplementation on organic anion and osmolyte content and excretion in rat polycystic kidney disease. Biochem Cell Biol. 1998;76;553-559.
19. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95-120.
20. Thompson LU. Experimental studies on lignans and cancer. Baillieres Clin Endocrinol Metab. 1998;12:691-705.
21. Thompson LU, Rickard SE, Orcheson LJ, et al. Flaxseed and its lignan and oil components reduce mammary tumor growth at a late stage of carcinogenesis. Carcinogenesis. 1996;17:1373-1376.
22. Serraino M, Thompson LU. The effect of flaxseed supplementation on the initiation and promotional stages of mammary tumorigenesis. Nutr Cancer. 1992;17:153-159.
23. Yan L, Yee JA, Li D, et al. Dietary flaxseed supplementation and experimental metastasis of melanoma cells in mice. Cancer Lett. 1998;124:181-186.
24. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95-120.
25. Sung MK, Lautens M, Thompson LU. Mammalian lignans inhibit the growth of estrogen-independent human colon tumor cells. Anticancer Res. 1998;18:1405-1408.
26. Sung MK, Lautens M, Thompson LU. Mammalian lignans inhibit the growth of estrogen-independent human colon tumor cells. Anticancer Res. 1998;18:1405-1408.
27. Thompson LU. Experimental studies on lignans and cancer. Baillieres Clin Endocrinol Metab. 1998;12:691-705.
28. Thompson LU, Rickard SE, Orcheson LJ, et al. Flaxseed and its lignan and oil components reduce mammary tumor growth at a late stage of carcinogenesis. Carcinogenesis. 1996;17:1373-1376.
29. Prasad K. Dietary flax seed in prevention of hypercholesterolemic atherosclerosis. Atherosclerosis. 1997;132:69-76.
30. Prasad K. Reduction of serum cholesterol and hypercholesterolemic atherosclerosis in rabbits by secoisolariciresinol diglucoside isolated from flaxseed. Circulation. 1999;99:1355-1362.
31. Arjmandi BH, Khan DA, Juma S, et al. Whole flaxseed consumption lowers serum LDL-cholesterol and lipoprotein(a) concentrations in postmenopausal women. Nutr Res. 1998;18:1203-1214.
32. Jenkins DJ, Kendall CW, Vidgen E, et al. Health aspects of partially defatted flaxseed, including effects on serum lipids, oxidative measures, and ex vivo androgen and progestin activity: a controlled crossover trial. Am J Clin Nutr. 1999;69:395-402.
33. Tarpila S, Kivinen A. Ground flaxseed is an effective hypolipidemic bulk laxative [abstract]. Gastroenterology. 1997;112:A836.
34. Jenkins DJ, Kendall CW, Vidgen E, et al. Health aspects of partially defatted flaxseed, including effects on serum lipids, oxidative measures, and ex vivo androgen and progestin activity: a controlled crossover trial. Am J Clin Nutr. 1999;69:395-402.
35. Arjmandi BH, Khan DA, Juma S, et al. Whole flaxseed consumption lowers serum LDL-cholesterol and lipoprotein(a) concentrations in postmenopausal women. Nutr Res. 1998;18:1203-1214.
36. Tou JC, Chen J, Thompson LU. Flaxseed and its lignan precursor, secoisolariciresinol diglycoside, affect pregnancy outcome and reproductive development in rats. J Nutr. 1998;128:1861-1868.
37. Thompson LU. Experimental studies on lignans and cancer. Baillieres Clin Endocrinol Metab. 1998;12:691-705.
38. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95-120.
39. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95-120.
40. Wanasundara PK, Shahidi F. Process-induced compositional changes of flaxseed. Adv Exp Med Biol. 1998;434:307-325.
41. Wanasundara PK, Shahidi F. Process-induced compositional changes of flaxseed. Adv Exp Med Biol. 1998;434:307-325.
42. Facsicule 1. Lini semen, linseed. In: European Scientific Cooperative on Phytotherapy. Monographs on the medicinal uses of plant drugs. Dusseldorf, Germany:IDW-Verlag. 1997:1-5.
43. Hutchins AM, Martini MC, Olson BA, et al. Flaxseed consumption influences endogenous hormone concentrations in postmenopausal women. Nutr Cancer. 2001;39:58-65
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Interesting read.
...which is true....but the butt kicking is more accurate a summary