September 2015 Issue
The Link Between Diet and Breast Density
By Kathy Hardy
Vol. 17 No. 9 P. 42
Studies suggest dietary patterns may lead to an increased risk of dense breast tissue, a possible risk factor for breast cancer.
Research into potential causes of dense breast tissue is beginning to emerge from the shadows of the better-known work in the area of breast cancer. One of the potential causes of dense breast tissue under investigation is diet and nutrition. In fact, the possible association between dietary choices and breast density has become an emerging area of discussion among epidemiologists, RDs, and other respected researchers in the cancer field.
This article discusses what breast density is, as well as its association with dietary factors and breast cancer risk.
A Cancer Risk Factor
Dense breast tissue is composed of less fat and more connective tissue, which appears white on X-ray images created with mammography—the frontline tool of breast cancer screening. Cancer also appears white on a mammogram, and if cancer is present, the tumors often are hidden behind the dense tissue. Women with dense breast tissue are considered to be at greater risk of having undiagnosed breast cancer due to this masking effect. If a tumor is hidden by dense breast tissue, it may go undetected. Early detection is vital in diagnosing breast cancer.
According to the American Cancer Society (ACS), breast cancer is the most common cancer among women in the United States, other than skin cancer. Breast cancer also is the second leading cause of cancer death in women, after lung cancer. When considering risk factors for breast cancer outside a woman's control, the ACS lists, among other things, genetics, family history, personal history, and dense breast tissue. Current guidelines from the American College of Radiology, the Society for Breast Imaging, and the ACS recommend that women receive annual mammograms beginning at age 40, even if they don't show symptoms or have a family history of breast cancer.
As a result of growing concerns regarding the effect of breast density on breast cancer occurrence, states are adopting mandatory notification legislation. In the five years since Connecticut enacted the first law mandating dense breast notification, 23 more state legislatures signed similar laws and more are pending. In addition, a proposed national breast density and mammography reporting act has been reintroduced in Congress, potentially increasing the number of women in the United States who will be learning the status of their breast tissue.
With the proliferation of news regarding dense breast notification, there's considerable interest in any associations between certain lifestyle factors, such as diet, and how women may develop dense breast tissue in the first place, beginning with their dietary patterns in childhood.
The ACS's website references certain dietary choices among its list of risk factors for breast cancer—alcohol consumption and a diet that results in women becoming overweight or obese—labeling this behavior "lifestyle-related risk factors for breast cancer." However, the topic of a potential link between diet and breast density is relatively new.
As the ACS states, breast density is linked to an increased risk for women to develop breast cancer, as compared with women with less dense breasts. While this is just one factor to consider in the overall picture of breast cancer prevention, researchers are now considering possible lifestyle influences that could cause women to develop dense breast tissue, even going back to when they were young children.
Dietary Energy Density
Researcher Linda G. Snetselaar, PhD, RD, LD, FAND, an epidemiology professor in the College of Public Health at the University of Iowa in Iowa City, approaches her work from the perspective of young women, particularly those who haven't yet reached puberty. She was recently involved in a study that, for the first time, suggests a potential positive association between dietary energy density and breast density among young women, particularly those who were overweight as children. She says that this study, which appeared in the March 2015 issue of the Journal of the Academy of Nutrition and Dietetics, is significant not only for the age group being examined but also for the overreaching perspective of the potential effects of fats, particularly saturated fats, on the development of dense breast tissue.
As stated in the study findings: "Breast density is modifiable and diet may be a contributing factor. Most research to date regarding dietary influences on breast density has focused on single foods or nutrients. Few studies have addressed the effects of overall diet on breast density, despite the fact that it may more aptly account for the complex interactions among foods consumed as components of diets."
"The idea is to try and see if there's any effect or a direct or established risk of breast density," Snetselaar says. "Body fat could impact breast cancer through breast density. The breast density aspect of our research is new to the equation."
She explains that in this study, researchers observed a "significant positive association" between food-only energy density (vs energy density from caloric beverages) and a woman's percentage of dense breast volume. According to the study, each 1 kcal/g unit increase of food-only energy density resulted in a 25.9% increase in quantity of dense breast volume.
Snetselaar says the dietary energy density study was a secondary analysis stemming from the Dietary Interventional Study in Children (DISC), the results of which were published in December 1993 in the Journal of the American Dietetic Association. She says that study data from this multicenter, randomized, controlled clinical trial that focused on reducing low-blood cholesterol in children showed safety in reducing saturated fat intake in children.
"You need to be careful when reducing fat intake in children," Snetselaar says. "You could end up with more eating disorders or iron deficiency, which is a particular concern in girls. In the DISC study, a low-fat diet was found to be as safe as a regular American diet. Taking information from the DISC study, we proceeded with the dietary energy density study, looking at the idea that there could be some association between BMI and breast density."
The ability to gather and review longitudinal data from girls aged 8 to 10 and then review data from those same subjects once they reach the ages of 25 to 29 is important in looking for dietary patterns and their health effects, as they pertain to breast density, Snetselaar says.
"Using data gathered from the DISC study, we have some indications of what was going on with these women when they were younger," she says. "Mammary cells grow and change rapidly during puberty. Diet history is important when considering fat consumption as a point of modification of cancer risk."
Down the line, Snetselaar says more studies involving larger numbers of participants over a longer period of time could provide an even clearer picture of the potential relationship between fat intake and dense breast tissue. "Finding a strong correlation between fat intake and its effect on youth can make it difficult to disentangle over time, when other risk factors could arise in a woman's life," she says.
Alcohol and Multiethnicity
With regard to other risk factors, the ACS also addresses alcohol consumption as a factor that's "clearly linked to an increased risk of developing breast cancer" and the risk increases with the amount of alcohol consumed. Taking that association one step further, Jasmine A. McDonald, PhD, an associate research scientist in the Columbia University Mailman School of Public Health's department of epidemiology, is involved in research that looks at a possible association between alcohol consumption and breast density as well.
"Researchers have been looking at alcohol as a possible risk factor for breast density," she says. "Many researchers think that if we could find markers that modify density, they could better identify breast cancer risks."
In a multiethnic study published in BMC Cancer in March, McDonald and other researchers reported, "Women who consumed more than seven servings of alcohol per week, especially women with a BMI greater than 25 kg/m2, had a higher percent of mammographic density."
In addition, "Alcohol consumption is associated with higher breast cancer risk," according to the study. "While studies suggest a modest association between alcohol intake and mammographic density, few studies have examined the association in racial/ethnic minority populations."
McDonald notes that this study is unique in that the population is multiethnic, where previous studies comprised "mainly white populations." Results show alcohol consumption is an equal risk factor across all ethnicities, she says.
"In this study, we looked at minority populations as well, to see if maybe there were different results across minority populations when it comes to breast density," she says. "We didn't see any difference. With that, the message regarding alcohol consumption as a risk factor in breast cancer and breast density would be the same across ethnicities."
Studies looking at an association between alcohol consumption and dense breast tissue would benefit from more long-term data, McDonald says. Longitudinal data would allow researchers to examine the effects of behavior changes over time.
"Studies now looking at current consumption rates give us the association between alcohol and breast density," she says. "A study over a longer period of time would show if you can alter the effect of alcohol on breast density over time. We could answer the question of whether or not people could decrease breast density."
McDonald says that prospective studies would enable researchers to gather information from earlier points in patients' lives, and then follow them until they start to get regular mammograms.
Also in agreement regarding breast cancer and potential density risks associated with alcohol consumption is Giske Ursin, MD, PhD, director of the Cancer Registry of Norway. Established in 1951, the Cancer Registry of Norway is, Ursin says, one of the oldest national cancer registries in the world. All physicians in the country are legally required to notify the registry of new cancer cases; even instances of suspected cancer must be reported. The registry receives approximately 140,000 notifications of cancer each year; of those, almost 30,000 are newly diagnosed.
The registry is responsible for all national cancer screening programs and operates with a goal of preventing cancer deaths by discovering cancer or precancerous lesions as early as possible.
Regardless of causation, Ursin stresses the importance of early detection and the role that dense breast tissue can play as a risk factor for breast cancer. She's examined density in women both in the United States and in Norway, along with the effects of both genetic variants and various reproductive and lifestyle factors on density, such as alcohol consumption.
In a recent Norwegian study, Ursin and other researchers examined the role of vitamin D in breast cancer development, finding "inconsistent evidence" of an association between vitamin D and both breast cancer and dense breast tissue. The study, which appeared in the May issue of PLOS ONE, included data from women aged 50 to 69 who ingested vitamin D in the same month they underwent a mammogram. According to the study, vitamin D intake is a significant overall health factor in Norway, a country with limited sunlight exposure for a large part of the year.
"We don't yet have clear evidence of any foods or nutrients that could potentially prevent someone from developing dense breast tissue," she says. "However, we do know that when it comes to foods women should avoid, alcohol is a risk factor for breast cancer, and it may also increase density."
Recommendations for Dietitians
With evidence regarding dietary associations and breast density continuing to evolve, nutrition professionals recommend following existing guidelines regarding risk factors.
"The research in this area is new," says nutrition consultant Karen Collins, MS, RDN, CDN, FAND. "As we continue to develop more advanced types of mammography, we can continue to study this. But what we know now will reduce the risk for cancer."
Collins refers to the American Institute for Cancer Research, which dedicates an area of its website (www.aicr.org) to tips for preventing cancer risk. They include subjects such as indulging in a more plant-based diet, keeping physically active, maintaining a healthful weight, and eliminating alcohol.
"While there may not be specific steps at this time for patients to follow regarding the prevention of dense breasts, these steps are already established good practices in the prevention of cancer," Collins says. "If they're found to also help prevent breast density, a breast cancer risk factor, that's an added benefit."
Researchers also stress the importance of starting early when it comes to making dietary choices that could help prevent breast cancer. Ursin says that starting young is a good preventive method parents can introduce to their children.
"The most important thing parents can do is ensure that their kids maintain a healthy diet and stay physically active," Ursin says. "Good habits learned early are more likely to stay with girls as they grow older."
Snetselaar agrees, adding that parents should consider their children's "first foods" as a way of helping to prevent future disease as their children grow to adulthood. "Children who learn to eat good foods early in life will accept those foods as comfort food later in life," she says. "They learn to love them early and will continue to love them throughout their lives."
— Kathy Hardy is a freelance writer and editor based in Phoenixville, Pennsylvania.