Four researchers kicked off the first in our Pathways Breast Cancer Study webinar series, Thriving and Breast Cancer: What we’ve learned from the Pathways Study, in February 2023. They gave an overview of the study and the findings so far about the relationship between diet patterns, Vitamin D, and length of survival and the risk of breast cancer recurrence.
After they presented, members of the Pathways Community Advisory Board asked some questions posed by webinar participants and the speakers answered more questions from the audience. You can find some general resources from the American Institute for Cancer Research on a healthy diet for cancer prevention and for healthy eating after a cancer diagnosis. For general guidance on Vitamin D, go to this NIH factsheet.
Following are questions and answers about general diet guidelines, specific foods and drinks, Vitamin D and supplements, and a few about the study and methods that the panelists answered after the webinar.
General Diet Guidelines
Q. I was surprised that diet isn't necessarily linked to breast cancer 5 year survival rates–did I understand this correctly?
What we presented is that diet is related to survival, but we did not report specifically on 5-year survival rates. We found that more healthy dietary patterns were associated with better survival. What we also noted was that there was no evidence of association with breast cancer-specific outcomes, either recurrence or breast-cancer-specific death. Thus, better survival is probably driven by non-breast cancer causes. We know that in the long run, women with breast cancer are at greater risk for heart and other cardiovascular diseases compared to the general population, and diet is an important factor influencing survival. The Pathways Study specifically showed that eating patterns that fit with the DASH diet, the healthy plant-based diet, and especially the American Cancer Society nutrition guidelines were strongly associated with better survival outcomes for women with breast cancer.
Q. Would you say that the recommendations that are coming out of your research are generally advisable for the rest of the population as well? I may be missing the subtle differences, but I feel like I'm not hearing recommendations that are terribly different from good diet guidelines for the general population.
Yes, on one level all of the healthy eating patterns that we examined in Pathways lead to better outcomes. However, the Healthy Eating Index (which measures how similar one’s diet is to the Healthy Eating Guidelines from the USDA/HHS) was only weakly associated with better outcomes among Pathways participants. On the other hand, the American Cancer Society (ACS) nutrition guidelines, the DASH (Dietary Approaches to Stop Hypertension) diet, and the healthy plant-based diet all are better options for women with breast cancer in our models, especially if they are concerned about heart and other cardiovascular diseases. These diets encourage fruits and vegetables, whole grains (not refined grains) and discourage red and processed meats.
Q. Do diet and exercise play the same role in those with BRCA mutations and those without? Do we know?
This is a great question, and something that we don't know. I'm not certain we can address this in the Pathways Study, but we may be able to. We have not looked specifically for BRCA mutations in the Study genotyping assays, although some participants may be tested in the clinic, especially when breast cancer occurs at younger ages or with a family history. While there is little information on this topic, our best estimate is that lifestyle factors are likely to play an important role in people with and without known cancer-related genetic mutations.
Q. Fasting seems to be in vogue. Is it safe? Does it decrease risk of breast cancer recurrence or increase length of life?
Preliminary studies, not from the Pathways Study, suggest that fasting in some patients who have cancer is safe, unless they have other conditions, such as hypoglycemia (low glucose levels). Emerging data showing intermittent fasting may decrease chemotherapy-related toxicity and tumor growth and cancer recurrence, but this is still preliminary and thus it is not currently recommended for patients undergoing active cancer treatment to partake in fasting. In addition, some people may need to ensure adequate food intake during active treatment, suggesting any role of fasting is complex. Unfortunately, the Pathways Study did not collect data that would allow us to examine this.
Specific Foods and Drinks
Q. Do processed meats to avoid include even those that are "Uncured" (those that don’t have nitrates and nitrites)? What in processed meats is associated with cancer?
In general, red meat (unprocessed) contains a high amount of heme iron that can be toxic if over absorbed by the body, although this impact is unlikely for the amounts of red meat consumed by most people. Red meat, including processed or cured meats and unprocessed meats, are all linked to an increased risk of cancer, although the risk is higher for processed meats. When red meat is processed into foods such as sausages, hot dogs, or bacon, there can be the production of N-nitroso compounds and carcinogens (substances known to cause cancer) such as polycyclic aromatic hydrocarbons (PAHs) and heterocyclic aromatic amines. These types of compounds are also found in air pollution. A review on this topic by the International Agency for Research on Cancer (IARC), a part of the World Health Organization, is available on the IARC Publications Website - Red Meat and Processed Meat.
Q. What about dairy products?
The current evidence regarding dairy products and breast cancer is mixed, whether for cancer prevention or improving outcomes in women with breast cancer. There are good reasons to suggest that dairy products may affect estrogen-sensitive breast cancer due to the possible high estrogen content of dairy foods. However, this has not yet been examined in the Pathways Study.
Q. What about soy milk and soy foods, cancer centers say they can be beneficial (rather than harmful or non-impactful) to breast cancer. What does your research say?
The primary concern that has been raised is related to phytoestrogens – plant compounds that have estrogenic activity (act like the hormone estrogen) such as genistein and daidzein – for which soy foods are among the richest sources. However, the best evidence suggests that traditional soy foods such as soy milk, tofu, and tempeh are likely to be beneficial – or at least not harmful – for women with breast cancer, including women with estrogen-receptor-positive (ER+) breast cancers. We plan to examine this question in the Pathways Study.
Q. What do we know about diet drinks and sugar substitutes in relation to breast cancers?
According to the National Institutes of Health, there is no solid evidence yet linking artificial sweeteners to cancer (Artificial Sweeteners and Cancer - NCI). However, similar to regular sugar and sugar sweetened beverages, the concern is more around its association with obesity, which may increase one’s cancer risk. The Pathways Study has not specifically looked at this yet.
Q. Is drinking alcohol okay?
In the context of cancer prevention, the American Cancer Society suggests not drinking any alcohol at all, however, if you choose to drink, that it be no more than 1 drink a day. (Past guidelines suggesting no more than 2 drinks a day for men are now changing to 1 drink a day.) A previously reported benefit of reduced heart disease with low to moderate alcohol intake has been called into question in recent years. The Pathways Study is currently in the middle of an alcohol analysis and will probably have results in the next year or so.
Q. What do we know about diet drinks and sugar substitutes in relation to breast cancers?
According to the National Institutes of Health, there is no solid evidence yet linking artificial sweeteners to cancer (Artificial Sweeteners and Cancer - NCI). However, similar to regular sugar and sugar sweetened beverages, the concern is more around its association with obesity, which may increase one’s cancer risk. The Pathways Study has not specifically looked at this yet.
Q. What about the difference in eating organic versus conventional foods, or GMO foods; many questions were asked in earlier surveys. Was any correlation found?
We did look at differences between people who prefer organic foods and the rest of the population, and they tend to have higher income and formal education levels. But we have not yet looked at how they relate to the outcomes.
Vitamin D & Supplements
Q. Can you clarify the Vitamin D recommendations?
Vitamin D supplements are a safe and effective way to increase vitamin D levels. Vitamin D3 is more easily absorbed (bioavailable) than vitamin D2. The National Academies of Sciences, Engineering, and Medicine recommend 600 IU of vitamin D daily for ages 1-70 years and 800 IU for ages 71 and above, with an upper limit of 4,000 IU daily. This recommendation is primarily for bone health benefits, not for cancer protection, and some cancer researchers have voiced concerns of the recommended dose being too low. Data show that people with higher body mass index (BMI) may need a higher dose. Vitamin D supplements are generally well absorbed, there is no strong evidence to support the need to take zinc to help vitamin D absorption.
Q. What do you make of other studies such as the Vital study which seemed to show that high-dose vitamin D does not lower the risk of developing cancer?
Yes, vitamin D supplementation appears to have no effect on reducing the risk of breast cancer. But in our study higher vitamin D levels are associated with better survival for patients diagnosed with breast cancer and for prevention of recurrence.
Q. What about supplements other than Vitamin D? Has the Pathways Study found that other vitamins or minerals make a difference in length of life or chances of getting another cancer?
So far, we haven’t completed analyses of other vitamins or minerals in the Pathways Study in relation to the outcomes of length of life or chances of getting another cancer. We are currently looking at how some vitamins and minerals may interact with chemotherapy use in influencing these outcomes.
Study and Methods
Q. The study asked questions about experiences with structural racism but did not explore experiences with workplace sexism. I was wondering if that is a topic that bears investigation in future questionnaires.
Thanks for the suggestion. There are definitely some areas that we did not think to address back when we first started the study but are recognized as important areas.
Q. What is known about bone density and risk of breast cancer metastasis or recurrence in bone?
Some studies have shown that higher bone density is associated with an increased risk of breast cancer, possibly because of higher estrogen levels. The literature on bone density and cancer metastasis or recurrence to the bone is very limited and there has been no clear conclusion.
Q. Why is Vitamin D going down with time in participants, is it diet or cancer biology or treatment induced?
I would like to clarify that we did not show that vitamin D goes down with time in Pathways Study participants. The Kaplan-Meier survival curves that were shown are the survival probabilities, which goes down in any population as we age. The key point of the KM curves is that there is separation of the curves in different colors, indicating different levels of survival probably. Our data showed patients with higher vitamin D levels have a higher survival probability than those with lower vitamin D levels.
Links Shared During Webinar
Catherine Thomsen
For slides and bios visit the Pathways Breast Cancer Study Webinar page
Sign up for Zero Breast Cancer emails
Check out Zero Breast Cancer Survivorship Factsheets
Learn more about the Pathways study
Links from Dr. Larry Kushi
American Cancer Society nutrition and physical activity guideline for cancer survivors
Postdiagnosis body fatness, recreational physical activity, dietary factors and breast cancer prognosis: Global Cancer Update Programme (CUP Global) summary of evidence grading
Links from Dr. Isaac Ergas
Elizabeth M Cespedes and Frank B Hu. Dietary patterns: from nutritional epidemiologic analysis to national guidelines
American Cancer Society. Guideline for Diet and Physical Activity
American Institute for Cancer Research. New Dietary Guidelines Committee Report Aligns with AICR Recommendations
USDA/HHS Guidelines for Americans 2020-2025 Report
American Cancer Society Guideline for Diet and Physical Activity
Harvard Health Mediterranean Diet
DASH (Dietary Approaches to Stop Hypertension) Diet
Ergas IJ, Cespedes Feliciano EM, Bradshaw PT, Roh JM, Kwan ML, Cadenhead J, et al. Diet Quality and Breast Cancer Recurrence and Survival: The Pathways Study. JNCI Cancer Spectr. 2021; 5:pkab019:
Satija A, Bhupathiraju SN, Spiegelman D, Chiuve SE, Manson JE, Willett W, et al. Healthful and Unhealthful Plant-Based Diets and the Risk of Coronary Heart Disease in U.S. Adults. J Am Coll Cardiol. 2017; 70:411-22:
INTERESTED IN METHODOLOGY (G-Computation)? Taubman SL, Robins JM, Mittleman MA, Hernan MA. Intervening on risk factors for coronary heart disease: an application of the parametric g-formula. Int J Epidemiol. 2009; 38:1599-611
Hippocrates on Wikipedia
Links from Dr. Song Yao
Dietary Reference Intakes for Calcium and Vitamin D from National Academies
Comment on the IOM Vitamin D and Calcium Recommendations from Harvard T.H. Chan School of Public Health
Vitamin D Fact Sheet for Health Professionals from National Institutes of Health Office of Dietary Supplements
The 2017 JAMA Oncology paper on Vitamin D and breast cancer outcomes from Pathways Study
Association of Body Weight with Response to Vitamin D Supplementation and Metabolism
