The Biomechanics of Bras and Lymphatics and the Link to Breast Cancer

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Sydney Ross Singer, Medical Anthropologist

2/17/2024

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All biological systems operate in the same physical universe as all other matter, and the same principles of physics that apply to the stars, planets, moons, mountains, missiles, also apply to eyes, brains, muscles, nerves, and cells. This means you can apply physics to the human body to understand how it works, and what we do to our bodies that stop them from working properly.

Mechanics is a branch of physics that deals with the physics of bodies, including our bodies, and the forces that work on them, such as pressure, torque, tension, adhesion, compression, constriction, and other physical impacts on the body. Biomechanics is the field that examines these physical forces in the context of biological systems. 

Biomechanic research into the structure and function of the tissues of the body and how they physically work have led to some important discoveries regarding the lymphatic system. The mechanical forces involved in the operation of the lymphatic system have been poorly understood, and new research has shown that how wearing tight bras can cause breast cancer by compressing the lymphatic system in the breasts.

The link between breast cancer and bras was first publicized in 1995, when my wife and I performed the world’s first study specifically examining the bra-cancer link. We interviewed over 4700 women, half of whom had breast cancer, about their past attitudes and behaviors regarding bra usage, including tightness and time worn daily, and found a significant link with breast cancer incidence. 

The theory for this link was that tight bras interfere with the lymphatic drainage in the breasts. The lymphatics are easily compressed and are responsible for lymph fluid drainage from the tissues, removing toxins, tissue debris, and waste products from cellular metabolism. The lymphatics also serve as the circulatory pathway of the immune system. Tiny lymphatic capillaries transport lymph from the tissues through lymph nodes, which serve as immune sentinels looking for infections and developing cancer cells. Ultimately, the lymph fluid returns to the bloodstream. 

The circulation of the body depends on blood and lymph being free to flow unobstructed. When the lymphatics are not able to flow properly, the lymph fluid backs up, causing lymphedema. This results in tissue congestion with lymph fluid, which can lead to swelling, pain, and more.

The lymphatic system does not have the same type of internal pressure as the bloodstream, which has a heart. The lymphatics originate in the tissue spaces, and has been thought to passively drain, usually against gravity, to the lymph nodes. For example, the breasts mostly drain their lymph up to the armpit, or axillary, lymph nodes. 

How does lymph go against gravity with no pressure?

The secret is that the lymphatics have one-way valves to keep fluid going in the right direction. When force is applied to the lymphatics by nearby muscles and from body movement, fluid is compressed inside the tiny lymphatic vessels, and the one-way valves propel the lymph to the next section. 

Recently, however, it has been discovered that the sections between the valves have thin muscle cells surrounding them that contract, making it a lymphatic pump. This has been called the intrinsic mechanism for lymphatic pumping, while external forces are called extrinsic mechanisms. Most research today is focused on this intrinsic pump, since it can potentially be affected by drugs.

As explained in an article in the journal Biology, Lymphatic Vessels and Their Surroundings: How Local Physical Factors Affect Lymph Flow

Lymphatic vessels drain and propel lymph by exploiting external forces that surrounding tissues exert upon vessel walls (extrinsic mechanism) and by using active, rhythmic contractions of lymphatic muscle cells embedded in the vessel wall of collecting lymphatics (intrinsic mechanism). Future research could take advantage of the recent discoveries on the molecular mechanisms and stimuli that can increase the lymphatic intrinsic pumping and use them to develop new drugs or aimed physical stimuli that could increase in the long term, the lymph drainage from areas of the body subjected to lymphedema.”

In the journal Lymphedema, the article, Biomechanics of the Lymphatic Circulation, states, 

The biomechanical nature of the lymphatic system plays a central role in all of its functions. Its ability to generate active pumping is key in fluid balance, as demonstrated by disruptions of the various pumping components that result in primary and acquired lymphedema. There are also serious implications for immune function if lymphatic transport is disabled. In this chapter, we present the basic biomechanical concepts necessary to understand lymphatic pumping function and discuss recent research on some of its specific components.” (Emphasis added.)

From these and other reviews and studies, it is clear that lymphatic impairment is immune impairment. This means increased incidence of cancer, since the immune system cannot properly fight developing cancer cells when the lymphatics are not properly moving lymph. Lymphedema, therefore, increases cancer incidence, along with the incidence of infections and other problems that cannot be adequately addressed by the immune system.

This was emphasized in the article, Lymph stasis promotes tumor growth, in the Journal of Dermatological Science.  Lymph stasis is related to lymphedema, and is stagnant lymph resulting from impaired lymph flow. 

(T)hese findings come as no surprise to us who for a long time have been aware that alterations in regional lymphatic flow may produce dysregulation in skin immune function and consequent oncogenesis. In fact, since 2002, our team has held the view that lymphedematous areas are immunologically vulnerable sites for the development of neoplasms as well as infections and immune-mediated diseases. In recent years, increasing evidence has confirmed this assumption.”

The journal Nature has an article, Biomechanical control of lymphatic vessel physiology and functions, which says, 

Until recently, the traditional pathology associated with malfunctions in lymphatics was lymphedema. However, with increasing research on lymphatics, novel functional roles of the lymphatic vasculature in diseases have been discovered. As such, the number of human diseases or disorders associated with lymphatic defects has increased, and inflammatory bowel diseases, eye diseases, neurological disorders, obesity, and cardiovascular diseases are now included. These new findings imply that restoring optimal lymphatic function may be a promising nonconventional strategy to managing these diseases. Thus, a deeper understanding of the mechanisms regulating lymphatic physiology and functions will be useful for the design of such an approach.” (Emphasis added.)

This means that it is important to make sure your lymphatics are functioning properly. And when it comes to the breasts, we must ask whether wearing bras interferes with lymphatic flow. 

Biomechanics have studied the bra and its impact on the breasts, especially for sports bras.  Their goal is to provide external support for the breasts to minimize movement without compression. As explained in the article, Mechanical analysis of breast–bra interaction for sports bra design, in the journal Materials Today Communication, 

Sports bras which are usually tight-fit and made of elastic materials are used to provide firm support to the breast and reduce the displacement. It is classified into two main types. Compression bras flatten the two breasts together against the chest wall to reduce the force momentum of the breast mass to the thorax. Encapsulation bras have two full-coverage cups to encircle the breast boundaries with individual support for the two separated breasts. The tension caused by stretched bra fabrics provides the breast support through compression, the cup pad even strengthen (sic) the support through interaction with the breast. However, if such interaction is too strong, it causes another problem, pressure discomfort. Comfortable brassieres should suppress movements of the breast as far as possible with minimum clothing pressure. Even if the brassiere fits the breast perfectly, however, the clothing pressure differs among subjects because of individual differences in the breast shape.” (Emphasis added.)

The article, A study to evaluate pressure distribution of different sports bras, in the Journal of Engineered Fibers and Fabrics, states, 

The pressure from the bra is among the most critical factors that affect the wearer’s health and comfort. The pressure of a sports bra on the wearer can irritate the skin and decrease blood flow when the pressure value of the bra is greater than the human’s tolerance limit. For this reason, the device used to measure the pressure of the bra on the human body should be very accurate and human­ friendly.

Many bra designers focus on biomechanical issues, as shown in this 2021 article in the International Journal of Environmental Research and Public Health, entitled, A Digital-Based Healthy Bra Top Design That Promotes the Physical Activity of New Senior Women by Applying an Optimal Pressure. It explains the problem they are trying to solve with a new bra for older women. 

Bra use can reduce physiological and physical functions because of clothing pressure, which can be a problem for new senior women starting to lose physical function. The present study presents a bra top design development method for promoting new senior women’s physical activity by identifying problems related to bras’ effects on women’s health and minimizing clothing pressure.”

The article continues, 

According to previous studies that examined the effects of bra use-related clothing pressure on the physiological response of the human body, bra straps and wires were the biggest contributors to clothing pressure; furthermore, wearing a bra that compresses the breast area for a long period of time puts placed pressure on the heart and affected blood circulation and lymph flow, as the bra surrounds the breast horizontally, it interferes with breathing and the circulation of lymph and blood flow. Furthermore, studies have found that it stiffens surrounding muscles and causes neck and back pain. Previous studies have suggested that the clothing pressure was relatively high in compression-style sports bra tops with reinforced motion function, thus involving a high risk of causing physiological disorders when worn for long periods.”

The bra industry clearly knows about these hazards of bras, which may explain the recent trend towards looser models, and women opting to be bra-free. 

This makes sense of the numerous studies that show the tighter and longer the bra is worn the higher the risk of breast cancer rises. My research, the 1991-93 US Bra and Breast Cancer Study, published in the book, Dressed to Kill, found that bra-free women have about the same risk of breast cancer as men, while the tighter and longer the bra is worn the higher the risk rises, to over 100 times higher for a 24/7 bra user compared to a bra-free woman. 

The 2015 study, Comparative study of breast cancer risk factors at Kenyatta National Hospital and the Nairobi Hospital, in the Journal of African Cancer, found that, 

Women who wore brassieres all the time, even when in bed were significantly associated with breast cancer occurrence as compared with those who never wore brassieres, or those whom only did so on important occasions (p<0.001). The wearing of brassieres, particularly underwire types or those that fit tightly, has been proposed to increase the risk of breast cancer. Singer and Grismaijer published their report in the book called ‘Dressed to Kill’, which describes a study they conducted. They reasoned that brassieres cause physical constriction that reduce lymphatic circulation, resulting in the retention of carcinogenic toxins. Unfortunately their work was never accepted for publication, and to date, there have been no scientifically valid studies that support the claim that brassieres may be associated with breast cancer occurrence. Ours does. To add to their theory, carcinogens released from blocked lymphatics may cause epigenetic changes impacting on cellular downstream signaling that may culminate in cancer.”

A 2016 study in the Journal of Oncology Research and Treatment, entitled, Wearing a Tight Bra for Many Hours a Day is Associated with Increased Risk of Breast Cancer, found that, 

This study demonstrated a correlation between wearing a tight bra for several hours per day and an increased risk of developing breast cancer….The bra is the only article of clothing that tightens the whole organ that it covers, and the repetitive and chronic direct trauma of this garment pressing all quadrants of the breast could lead to disease through the radial scars…The system of lymphatic vessels has been called an “information superhighway” because lymph contains a wealth of information about local inflammatory conditions in upstream drainage fields. Bras and other external tight clothing can impede flow, cutting off lymphatic drainage so that toxic chemicals are trapped in the breast.”

In 2016, the World Journal of Meta-Analysis, the article, Brassiere wearing and breast cancer risk: A systematic review and meta-analysis, found 12 case controlled studies on bras and breast cancer and concluded, “the meta-analysis shows statistically significant findings to support the association between brassiere wearing during sleep and breast cancer risk.”

Clearly, tight clothing that interferes with the lymphatics can cause disease, including cancer. Bra bioengineers know this. But what about the lymphatics bioengineers? They are more focused on finding ways to impact the intrinsic pumping of the lymphatics, and don’t really focus on the extrinsic factors. 

As quoted above in the Biology article, “Future research could take advantage of the recent discoveries on the molecular mechanisms and stimuli that can increase the lymphatic intrinsic pumping and use them to develop new drugs or aimed physical stimuli that could increase in the long term, the lymph drainage from areas of the body subjected to lymphedema.” That’s where the money is. Come up with some drug or machine that can treat lymphedema by altering the lymphatic muscles that pump lymph. 

The problem is that you cannot ignore extrinsic factors, like tight bras, when studying lymphatic flow. Intrinsic lymphatic pumping muscles will have a hard time pumping against compression from bras. These scientists studying lymphatics often cut a lymph vessel out of the body and test it in some apparatus; or they study lymphatics of non-human animals who don’t wear clothing. They seem oblivious to the factor of tight clothing, which is especially bad when considering breast lymphatics. You cannot study women’s breasts without knowing how long and how tightly they have been compressed into the chest by a bra.

Bra manufacturers know this. That’s why there are now several bra patents discussing the impact of bras on the lymphatics. For example, a 2012 patent for a Breast Saver: And ergonomic dynamic bra with combo cups, claims,

“Tight fitting bras restrict and compress the lymphatic system in the breast.The Lymphatic system is responsible for  flushing out bodily wastes and toxins and this could become impeded with compression.  Thus the lymph nodes, acupressure points, and the circulatory pathways in the breast and armpit areas, may be restricted and prevented from doing their job by tight fitting bras, and may result in toxins to accumulate in the breast tissue.”

It’s time for the bioengineers to get together with the doctors and cancer experts and discuss how bras impair the lymphatic system and increase cancer incidence. Currently, the cancer industry is stonewalling this issue. For example, the American Cancer Society claims the link between breast cancer and bras is unfounded

Online and social media rumors and at least one book have suggested that bras cause breast cancer by obstructing lymph flow. There is no scientific or clinical basis for this claim, and a 2014 study of more than 1,500 women found no association between wearing a bra and breast cancer risk.”

Apparently, the ACS has not seen any of the research mentioned in this article. 

And the study they suggest does not support the bra-cancer link was done deliberately biased and flawed. The study was published in the journal Cancer Epidemiology, Biomarkers, and Prevention, and was entitled, Bra Wearing Not Associated with Breast Cancer Risk: A Population-Based Case–Control Study. It states, 

There has been some suggestion in the lay media that bra wearing may be a risk factor for breast cancer based on the potential for bras to impede lymph circulation and drainage and thus interfere with the process of waste and toxin removal. However, there is a scarcity of credible scientific studies addressing this issue. To our knowledge, the only epidemiologic (sic) evidence on bra wearing and breast cancer risk comes from a case–control study published in 1991, which reported a nonstatistically significant two-fold higher risk among premenopausal women who wore a bra versus those who did not, but no elevation in risk was observed for postmenopausal women. Given that questions in the lay media have been raised about breast cancer risk and bra wearing, we evaluated relationships between various aspects of bra wearing and breast cancer risk among postmenopausal women enrolled in a population-based case–control study.” (Emphasis added.)

This study is interesting because it reveals a bias. The quote above from this study referenced another study, from 1991, which found decreased breast cancer risk in bra-free women. That study, in the European Journal of Cancer, was entitled, Breast size, handedness and breast cancer risk. It found that breast size did not affect cancer incidence in premenopausal women, but did in postmenopausal women. However, lower cancer rates for bra-free women only seemed to show in the premenopausal group, not the postmenopausal group. The researchers were not looking for a bra-cancer link, and only used bra size as an estimate of breast size. They could not explain their finding of 100% higher risk for breast cancer in bra users compared to bra-free women. And their proposed explanation was illogical. 

Premenopausal women who do not wear bras had half the risk of breast cancer compared with bra users (P about 0.09), possibly because they are thinner and likely to have smaller breasts. Among bra users, larger cup size was associated with an increased risk of breast cancer (P about 0.026), although the association was found only among postmenopausal women and was accounted for, in part, by obesity.” (Emphasis added.)

Note that breast size is only a slight risk factor for older women, not for younger women. But their proposed guess for their findings in young women who were bra-free and had lower breast cancer rates was that they were likely to have smaller breasts. But breast size did not affect cancer rates for younger women, so this cannot be the answer. 

Interestingly, the study above that referenced this study and did not find a bra-cancer link decided in their study design to only look at postmenopausal women, for whom the 1991 study found no bra effect. Why test the negative result seen in postmenopausal women and not the positive result seen in younger women? If you want to study a bra-cancer link, why not use the group for which this link was positive? 

Making matters worse, this 2014 study of postmenopausal bra users excluded any bra-free women, so there was no control group for comparison. 

Because bra wearing was ubiquitous among our participants, we were unable to compare risks among women who never wore a bra to those who regularly wore a bra, and instead, our primary comparison was based on average number of hours per day women wore a bra.”

One can only speculate as to why the American Cancer Society would discourage research into the bra-cancer link, and only cite biased research without giving its limitations while ignoring other studies which show a link. They certainly seem invested in the status quo, and in biochemical and not biomechanical solutions. 

Women have a right to know that the bra they are dutifully wearing has the potential to harm their breasts and overall health, so they can make informed choices regarding bra usage. Society has become more accepting of women choosing comfort over fashion, and being comfortably bra-free is now popular, especially among younger women. It is hoped that this trend continues, and that the medical industry examine the evidence presented in this paper that shows the vital need of addressing the biomechanical impact of tight clothing on breasts and the rest of the body, on cancer development, and on overall health. 

Any tight clothing, including Ace bandages and other compression devices, any garment sold for “support”, will be tight by design, and interfere with the lymphatics. The body cannot fight infection or heal when the lymphatics are impaired. It’s time to stop creating that impairment with tight clothing, and let the lymph circulate.

References:

Underlines above are all hyperlinks to articles. In addition to the above, here are some resources. 

Breast Biomechanics: What Do We Really Know?

Biomechanics of Breast Support for Active Women

Sports Bra Pressure: Effect on Body Skin Temperature and Wear Comfort

Mechanical analysis of breast–bra interaction for sports bra design

Biomechanical control of lymphatic vessel physiology and functions

Lymphatic anatomy and biomechanics

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