What is a Lignan
Lignans are organic compounds found in the cell walls of plants. They are part of a family of compounds with estrogenic, anti-estrogenic and antioxidant activity. These phytoestrogens (estrogen like chemicals found in plants) can have a balancing effect on hormones. There are other classes of phytoestrogens. These other phytoestrogens are isoflavones, flavones, stilbenes and coumestans. The most extensively studied of these phytoestrogens are the soy isoflavones and the flaxseed lignans.
The health benefits of lignans highlighted in these studies include:
- breast cancer
- endometrial cancer
- prostate cancer
- cardiovascular disease
- brain function
- immune function
More than 24 different plant lignans
There are 24 different lignan precursors that have been identified so far. They are found in different concentrations in different plants. Their concentrations are highest in flax and sesame seeds as well as several types of bran. Below are a few lignans and which seeds and brans have the highest concentration of each.
- Pinoresin is concentrated in sesame seeds and rye bran
- Syringaresinol is concentrated in both rye and wheat bran
- Sesamin, is concentrated in sesame seeds
- Lariciresinol is concentrated in flaxseed, sesame seeds and rye bran
- Secoisolariciresinol is concentrated in flaxseed.
- Matairesinol is concentrated in sesame seeds
- Hydroxymatairesinol is concentrated in wheat bran
Converting Plant Lignans to Mammalian Lignans
The human body alone cannot process or use plant lignans. It is only when plant lignans are converted to mammalian lignans that they become bio-available. The two bio-available lignans are enterolactone and enterodial. Converting plant lignans to the mammalian lignans the human body can use is the job of the friendly bacteria that inhabit the intestinal tract. Once this conversion takes place, these mammalian lignans are shuttled to the liver. It is this final processing that allows the body to use the lignans in disease prevention and health maintenance.
The amount, of biologically active lignans, is directly related to the amount of plant lignans consumed and the bacteria responsible for the conversion and the general health of the digestive tract. Anything that influences the health of the intestines, even the use of antibiotics, effects the conversion of plant lignans to mammalian lignans. Studies have shown that antibiotic use within a year of testing for circulating levels of lignans, was associated with reduced serum enterolactone and enterodial
Links between plant and mammalian lignans
Secoisolariciresinol and hydroxymatairesinol are the only two plant lignans that have been scientific studies have directly linked to the mammalian lignan enterodiol and enterolactone. Flaxseed has been found to be the highest source of secoisolariceresinol while hydroxymatairesinol is found in abundance in the wheat bran.
Other foods sources high in these two important lignans are:
- sesame seeds
- sunflower seeds
- pumpkin seeds
- Brussels sprouts
- green and black tea
LIGNANS IN HEALTH AND DISEASE PREVENTION
Estrogenic and Anti-estrogenic Activities of lignans
Hormones are signaling molecules that influence cell function. They do this by binding to special receptors within a cell. Each hormone has a receptor that is specific to that hormone. Once bound to its receptor the hormone interacts with the cell's DNA to change how the genes that are sensitive to that hormone function.
Estrogen is a female hormone that it is found in both men and women. When estrogen binds to it's receptor, it interacts with DNA to change the expression of estrogen-responsive genes. Not only are estrogen receptors found in the tissues associated with reproduction, but many others as well. Many tissues contain estrogen receptors. These tissues include: male and female reproductive tissue, bone, liver, heart and surprisingly the brain. Although, like the estrogen made by the body, lignans bind to the estrogen receptors withing the cells, their effects are much weaker.
In the body, plant lignans are converted to the mammalian lignans, enterodiol and enterolactone. Research has shown that these mammalian lignans have the same mild estrogenic activity as the plant lignans from which they come. The estrogenic activity of lignans is proving to have far reaching effects on human health.
It has been found that these lignans in low doses mimic the effect of estrogen (estrogenic activity). This is what makes lignans so helpful with menopausal symptoms, osteoporosis and BPH. In high doses, however, lignans exhibits just the opposite. In high doses, lignans exhibit anti-estrogenic properties. Emerging research is showing that lignans can actually block or antagonize the effects of estrogen in some tissues. Scientists are eagerly pursuing this avenue of research. It is thought that these phytoestrogens work not only by mimicking estrogen (this helps in menopausal symptoms) but by preventing the formation of blood vessels to tumors thus restricting their growth and by disrupting the DNA inside tumor cells thus disrupting cell multiplication. By learning more about the estrogenic and anti-estrogenic effects of these compounds, scientists are hoping to unlock a key to why phytoestrogens show such promise in reducing the risks of hormone related cancers like breast, uterine, ovarian and prostate.
Lignans are proving themselves in other areas as well. Research is showing that lignans may help in areas like cardiovascular disease, elevated cholesterol and kidney disease. Preliminary studies in animals and humans suggest that lignans may be helpful in not only hormone sensitive cancers such as breast and prostate cancers but other cancers like colon cancer as well. Lignans are also showing themselves to be a new weapon in the arsenal against elevated cholesterol and as an antioxidant in the battle against cardiovascular disease. The use of lignan supplements are also proving useful in improving kidney function in various types of kidney diseases, especially lupus nephritis and polycystic kidney disease
WHAT THE STUDIES SAY
Lignans the link to preventing cancer?
There are two different types of breast cancer. They are called “estrogen receptor alpha-positive” or ERRa -positive breast cancer and “estrogen receptor alpha-negative” or ERa - negative breast cancer.
Era-negtive tumors are more aggressive and less responsive to treatment than Era-positive tumors.
In a study published the Journal of the National Cancer Institute in 2007, it was found that a diet rich in the lignans found in flaxseed, tea and other plants rich in lignans, may help curb breast cancer in post menopausal women. This study followed 58,000 post menopausal women from 1993 to 1997. These women were all in their early 50's and did not have breast cancer. The study followed their diet and lifestyle. It also tracked how often they consumed 208 foods and beverages. The researchers, including Francoise Clavel-Chapelon PhD, are from Frances Institut National de le Sante et de la Recherche.
Dr. Chavel-Chapelon and his collegues calculated the women's dialy dietary intake of lignans. On the average these women consumed between 0-5mgs of lignans per day with the average being 1mg per day. The women got their lignans from a variety of sources including fruits, vegetables, tea, coffee and grain products.
Of the 58,000 women followed, 1,469 developed breast cancer. Women with the highest intake of lignans were found to be 17% less likely to develop breast cancer than those with the lowest intake.
A recent prospective study from Denmark showed that Era-negative breast cancers but not Era-postive cancers were significantly lower in women with higher serum enterolactone concentrations (remember enterolactone is a mammalian lignan derived from plant lignans). The Era-negative cancers are much more aggressive and less responsive to treatment than Era-positive ones.
A study conducted in vitro or in the test tube, showed that lignans inhibit the growth of estrogen sensitive tumors.
Although these studies seem contradictory, it is believed by researchers that lignans have a balancing effect on hormones.
Endometrial and Ovarian Cancer
In a case-control study of lignans and endometrial cancer, women in the United States with the highest intake of plant lignans had the lowest risk of endometrial cancer. This risk however was only statistically significant in post menopausal women.
In a similar case-control study of lignangs and ovarian cancer, U.S. Women with the highest rate of lignan intake had the lowest rate of ovarian cancer.
BPH and Prostate Cancer
BPH is a non-cancerous condition where the prostate becomes greatly enlarged. This enlargement causes the urethra (the tube that carries urine from the kidneys to the bladder and runs through the prostate gland) to become compressed. This compression causes a number of problems. These problems include:
- frequent and overwhelming urge to urinate
- painful urination
- weak stream
- poor ejaculation
BPH affects an increasing number of older Americans, In fact, The American Urological Association estimates that BPH effects 50% of the men aged 50-60 and up to 90% of those over 80. Prostate cancer is an even greater concern. It is the second leading cause of cancer death among men in the United States.
The exact cause of BPH remains a mystery. It is believed that BPH like prostate cancer is caused by an overabundance of DHT. DHT or dihydrotestosterone, a derivative of testosterone and much more potent ,is involved in both BPH and prostate cancer. Too much of this hormone caused increased growth in the number of cells in the prostate gland. This increased growth results in BPH and prostate cancer. Scientific research has proven that by interfering with the conversion of testosterone of DHT the incidences of both BPH and prostate cancers decrease.
Here is what researchers are finding out about high lignan intake and both BPH and prostate cancer.
In the average man, only a small fraction of testosterone is available for the body to use. The rest of the testosterone is bound to a protein called SHBG or sex hormone binding globulin. Studies show a direct correlation between the amount of lignans in the diet and the amount of SHBG circulating in the body. The more testosterone bound up in the SHBG the less there is to convert into DHT. This means there is less DHT to cause uncontrolled growth of the prostate gland.
Some studies have also shown that lignans block the enzymes that convert testosterone to DHT.
While still others have linked high lignan concentrations is seminal fluid with a decreased incidence of prostate cancer. A recent study of 25 patients with cancer where given a low fat diet plus flaxseed. At the end of the study, these men showed a reduction in the levels of testosterone, a reduction in the reate of cancer cell growth that was measured by a reduced PSA (prostate specific antigen, a marker for prostate cancer progression).
This study was followed with one that used lignans alone. Lignans were combined in a test tube with human prostate cancer cells. The lignans alone were responsible for a reduction in the growth of these tumor cells. These studies support the theory that lignans are protective against BPH and prostate cancer.
Colorectal cancer is the third most common cancer and the third leading cause of cancer deaths. According to the National Cancer Institute, 112,300 new cases of colon cancer were diagnosed along with 41,420 new cases of rectal cancer The number of deaths from these cancers topped 52,000 and cost more that 8.4 billion dollars to treat..
A Canadian research team investigated the link between the intake of dietary phytoestrogens, including lignans, and colorectal cancers among cases and controls. The cases of colorectal cancers ranged in age from 20-74 years of age and the control group where age and sex matched to the cases. This is a population based study by the Ontario Familial Colorectal Cancer Registry. The OFCCR is one of six international sites participating in a study by the U.S. National Cancer Institute.
The study consisted of 1095 cases of colorectal cancer balanced with 1890 controls. These participants completed epidemiological questionnaires. These questionnaires covered the following areas:
- colorectal screening results
- medical condition
- reproductive factors
- physical activity
- and anthropometric measures
- food frequency diary
These Canadian researchers found that those with the highest dietary lignan intake had a considerable reduction in colorectal cancer risk. This link was also seen with an increased intake of isoflavones and
and increase intake of phytoestrogens, isoflavones and lignans.
A study of human colorectal cancer cells (SW480) showed that lignans actually prevented the growth of these cancer cells. By stopping their growth, the lignans caused what is known as apoptosis or cell suicide.
Preliminary research is showing that lignans may improve kidney function in various types of kidney disease. The research is especially promising in cases of lupus nephritis and polycystic kidney disease. However, if you are being treated for kidney disease, check with your health care practitioner before starting lignan supplements.
When taking lignan supplements, the recommended amount is between 30-50mg per day.
Studies with rats have shown that when pregnant rats were fed diets with over 10% flaxseed or purified lignan extracts gave birth to offspring with altered reproduction organs and functions. Because of this women who are pregnant or breastfeeding showed avoid supplementing with lignans and keep consumption of flaxseed or other high lignan foods to less that 25 grams per day.
Although studies the studies of lignans and breast cancer are positive, because lignans are phytoestrogens, women with previously diagnosed breast cancer should consult their health care practitioner before consuming large amounts of lignan rich foods or taking a lignan supplement.
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*Brassaci vegetables include all of the following:
broccoli, Brussels sprouts,
cabbage, cauliflower, swedes, and turnips as well as broccoli raab, collards, cress, kale, kohlrabi, mustard, and
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