Lignans as a dietary supplement
Lignans are natural compounds found predominantly in plants, particularly in flaxseed and sesame seeds, and are often promoted as dietary supplements for their potential health benefits. These compounds are classified as phytoestrogens, which means they can mimic estrogen in the body, possibly offering therapeutic effects related to hormone-sensitive conditions. Research suggests lignans may play a role in cancer prevention, particularly for breast and colorectal cancers, by interacting with estrogen receptors, although definitive proof of their efficacy is still needed through extensive clinical trials.
In addition to cancer prevention, lignans are associated with various other health benefits, such as improving cardiovascular health by lowering cholesterol and blood pressure, alleviating menopausal symptoms, and enhancing gut health. They may also have protective effects on brain function and offer antioxidant properties that combat oxidative stress. Flaxseed, the richest dietary source of lignans, can be consumed whole or ground, while its oil does not contain significant amounts of these compounds.
However, there are safety considerations; individuals, particularly women who are pregnant, breastfeeding, or have a history of estrogen-sensitive cancers, should approach lignan supplementation with caution and consult healthcare professionals for guidance. Overall, while lignans show promise as a dietary supplement, ongoing research is necessary to fully understand their benefits and appropriate usage.
Lignans as a dietary supplement
- DEFINITION: Natural substance promoted as a dietary supplement for specific health benefits.
- PRINCIPAL PROPOSED USES: None
- OTHER PROPOSED USES: Cancer prevention, elevated cholesterol, kidney disease, menopausal symptoms, hormone-related conditions, cardiovascular health, anti-inflammatory, antioxidant, gut health, cognitive function
Overview
Lignans are naturally occurring chemicals widespread within the plant and animal kingdoms. Several lignans, with intimidating names such as secoisolariciresinol, are considered phytoestrogens, plant chemicals that mimic the hormone estrogen. Phytoestrogens are especially abundant in flaxseed and sesame seeds. Bacteria in the intestines convert the naturally occurring phytoestrogens from flaxseed into two other lignans, enterolactone and enterodiol, which also have estrogen-like effects. “Lignans” here refers to these two specific lignans and 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), 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. Several other therapeutic uses for lignans have been proposed.
Sources
The richest source of lignans is flaxseed (sometimes called linseed), containing more than one hundred times the amount found in other foods. Flaxseed oil, however, does not contain appreciable amounts of lignans. Sesame seed is an equally rich source. Other food sources are pumpkin seeds, whole grains, cranberries, and black and green tea.
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 grams (g) daily. Cooking flaxseed apparently does not decrease the amount of lignans absorbed by the body.
Therapeutic Uses
Studies suggest that lignans may provide benefits for hormone-related issues, such as hormone-sensitive cancers and osteoporosis. They may also help alleviate some symptoms of menopause, such as hot flashes. Research indicates lignans can offer cardiovascular benefits by reducing cholesterol and blood pressure. Their antioxidant properties can protect against oxidative stress that may lead to cardiovascular issues, and they can also protect against other chronic health conditions. Other preliminary research suggests that flaxseed or lignans may improve kidney function in various types of kidney disease (specifically, lupus nephritis and polycystic kidney disease). Lignans have been suggested for their prebiotic properties to improve gut function and boost immune function. Finally, one study found that lignans may hold protective attributes for brain function and cognitive health.
Flaxseed or other treatments for kidney disease should be taken only under a doctor’s supervision because of the serious nature of these disorders.
Scientific Evidence
The most promising use for lignans is in cancer prevention. According to observational studies, people who eat more lignan-containing foods have a lower incidence of breast and perhaps colon cancer. This, however, does not prove that lignans are the cause of the benefit, for other factors in these foods, or in the characteristics of the people who consume these foods, may have been responsible. Double-blind, placebo-controlled studies are necessary to prove that a medical treatment provides benefits, and though few had yet been reported for lignans, in the twenty-first century, research expanded. Animal and test-tube studies offered additional 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 animals and reduced metastases from melanoma (a type of skin cancer) in mice. Test-tube studies have found that flaxseed or one of its lignans inhibited the growth of human breast cancer cells. The lignans enterolactone and enterodiol inhibited the growth of human colon tumor cells. Small studies in humans conducted in the 2010s showed the potential of lignans to lower the risk of breast cancer in postmenopausal women and prevent colorectal, blood, and lung cancers. While ongoing observational, laboratory, and animal studies appeared to support the claim that lignans could be a powerful cancer therapy, additional study in humans remained necessary.
In many of these studies, it is not clear whether lignans are responsible for the benefit seen because flaxseed contains many other substances. Animal and human studies have begun to examine specific lignans, and results seem to confirm that some of the positive effects probably come from the lignans themselves. Still, until more and better-designed trials are done, the precise effects of lignans on the human body or the precise dose needed to prevent cancer are not known.
As research expanded into lignans, more health benefits were discovered. Lignans are high in protein, fiber, omega-3 fatty acids, vitamins, and minerals, making them effective at treating chronic conditions. Small studies found lignans effective in lowering cholesterol and blood pressure and stabilizing blood sugar, suggesting they may help treat diabetes. A 2019 study revealed that lignan-rich foods were useful in preventing chronic diseases such as cancer and heart disease.
Safety Issues
Women who are pregnant or breastfeeding should avoid consuming large amounts of flaxseed or purified lignans. One study found that pregnant rats who ate large amounts of flaxseed (5 or 10 percent of their diet) or a purified lignan present in flaxseed gave birth to offspring with altered reproductive organs and functions, and lignans were also transferred to the baby rats during nursing. In humans, eating 25 g of flaxseed daily amounts to about 5 percent of the diet.
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 lignans, such as those in flaxseed, can stimulate specific cancer cells. Other studies found that lignans inhibit cancer cell growth. As with estrogen, lignan's positive or negative effects on cancer cells may depend on the dose, type of cancer cell, and levels of hormones in the body. Persons with a history of cancer, particularly breast cancer, should consult a doctor before consuming large amounts of flaxseed.
Bibliography
Coulman, K. D., et al. "Whole Sesame Seed Is as Rich a Source of Mammalian Lignan Precursors as Whole Flaxseed." Nutrition and Cancer, vol. 52, 2005, pp. 156-165.
Franco, Oscar H., et al. "Higher Dietary Intake of Lignans Is Associated with Better Cognitive Performance in Postmenopausal Women." The Journal of Nutrition, vol. 135, no. 5, 2005, pp. 1190-1195, doi.org/10.1093/jn/135.5.1190. Accessed 8 Oct. 2024.
Hallund, J., et al. "A Lignan Complex Isolated from Flaxseed Does Not Affect Plasma Lipid Concentrations or Antioxidant Capacity in Healthy Postmenopausal Women." Journal of Nutrition, vol. 136, 2005, pp. 112-116.
Hassanein, E. H. M., et al. "The Promising Antioxidant Effects of Lignans: Nrf2 Activation Comes into View." Naunyn-Schmiedeberg's Archives of Pharmacology, vol. 397, no. 6, 2024, pp. 6439-6458, doi.org/10.1007/s00210-024-03102-x. Accessed 8 Oct. 2024.
Hutchins, A. M., et al. "Flaxseed Consumption Influences Endogenous Hormone Concentrations in Postmenopausal Women." Nutrition and Cancer, vol. 39, 2001, pp. 58-65.
Meacham, Jared, et al. "The Top 9 Health Benefits of Flaxseed." Healthline, 26 Jan. 2024, www.healthline.com/nutrition/benefits-of-flaxseeds. Accessed 8 Oct. 2024.
Radcliffe, Shawn, and Jill Seladi-Schulman. "Flaxseeds Influence Gut Microbiome and May Reduce Breast Cancer Risk." Healthline, 8 Dec. 2023, www.healthline.com/health-news/flaxseeds-influence-gut-microbiome-and-may-reduce-breast-cancer-risk. Accessed 8 Oct. 2024.
Rodríguez-García, Carmen, et al. "Naturally Lignan-Rich Foods: A Dietary Tool for Health Promotion?" Molecules, vol. 24, no. 5, 2019, doi.org/10.3390/molecules24050917. Accessed 28 Aug. 2023.
Xiao, Hui, et al. "A Metabolomics Study on the Bone Protective Effects of a Lignan-Rich Fraction From Sambucus Williamsii Ramulus in Aged Rats." Frontiers in Pharmacology, vol. 9, 2018, p. 403133, doi.org/10.3389/fphar.2018.00932. Accessed 8 Oct. 2024.
Zhang, W., et al. "Dietary Flaxseed Lignan Extract Lowers Plasma Cholesterol and Glucose Concentrations in Hypercholesterolaemic Subjects." British Journal of Nutrition, vol. 99, 2008, pp. 1301-1309.