Nutraceuticals and the Risk of Breast Cancer
Apoptosis remains the most vital part of normal and abnormal cells. A defect in apoptosis is considered to be the main cause of cancer. The literature is full of studies investigating the reason for defective apoptosis that can be due to defect in the apoptotic pathway, such as enhanced mutation of genes, inactivation of death receptors etc. Nutraceuticals of plant origin that are mostly a part of our diet and nutrition have shown to have tremendous anti-cancer properties as studied in many in vitro experiments. Foods such as soy, ginger, garlic, green tea, and spices curcumin, cinnamon etc have shown encouraging results due to their effect on prompting apoptotic activity for cancerous cells as well.
Antioxidants such as Vit A, alpha and beta carotene, Lycopene Vit c, and Vit E have shown their neutralizing effect by trapping the free radicals or Oxygen reactive species and preventing the cellular damage. When the concentration of free radicals increases within the cell and is not neutralized by antioxidants and enzymes present in our body or as exogenous dietary antioxidants, this situation can lead to the damage of DNA and cell membranes. Damaged cells then can proliferate and initiate carcinogenesis. In case of breast cancer, it is proposed that damage to the DNA and cell membrane is the main cause of proliferation of cancer cells. A large number of studies have looked into the benefits and harms of using antioxidants post diagnosis for progression, survival and recurrence; however, the results have been inconsistent. This is most likely due to the heterogeneity of the population, age, exposure to toxins, types, combinations and doses of the supplements, and duration of treatment before and after diagnosis. For example, improved breast cancer survival was observed in a meta-analysis of cohort studies where patients used Vit C supplementation after diagnosis. [13-15] A large cohort study data analysis by Greenlee. H et al, showed that although Vit C was associated with decreased mortality and recurrence, post diagnosis cancer patients who used combination carotenoids had an increased risk of death but there was no increase in the risk of recurrence.
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The use of supplements, specially antioxidants such as Vit A, C, and E, have been criticized for causing interference in the effect of chemotherapy or radiation therapy and has always posed a question for the treating physicians and people practicing Alternative therapies. It is not clear if antioxidants actually protect only normal tissue and therefore decrease the toxicity of the cancer therapies or if conversely also protect the cancer cell or if antioxidants can indeed protect normal tissues from chemotherapy induced damage but does so without decreasing the efficacy of the chemotherapy. One study using the data from a large cohort study (Mamma Carcinoma Risk Factor Investigation) concluded that postmenopausal women with breast cancer have poor prognosis with concurrent use of antioxidants and suggested to avoid the use of antioxidants during their treatment phase with chemotherapy.
Vitamin C is the most commonly used dietary supplement known to influence cancer cell through its antioxidant properties and neutralization of free radicals in breast cancer patients. Several studies including in vitro, observational and clinical trials suggest that vitamin C during chemotherapy and radiation therapy may protect cancer cells as well along with protecting the normal cells. On the other hand, results from some observational studies suggest that Vit C intake and survival post diagnosis can reduce the risk of mortality and improve survival [13, 16, 17] H R Harris et al studied the association between vitamin C and mortality in breast cancer patients based on the factors related to reactive oxygen species such as obesity, age and history of smoking. The group observed that Vitamin C had a stronger inverse relationship with mortality in breast cancer patients who were 65 years and older- Table 1 . Vit C has been shown to demonstrate cytotoxicity at higher doses without exerting its negative effect on normal cells. A recent study published in 2019, concluded that higher doses of Vit C combined with chemotherapeutic agents, can be harmful to cancer cells and can have therapeutic advantages. According to the study, high-dose of vitamin C >10 mM significantly reduced the cell viability of specifically MCF-7 cells (human breast adenocarcinoma cell lines) and almost in all other breast cancer cell lines and also the same effect was seen when high-dose vitamin C was combined with tamoxifen.
For centuries soy products have been used for potential health benefits. Although most of the soy products have been used by people with chronic diseases such as diabetes, hypertension and heart diseases, however, its benefit are also linked with breast cancer survival. The evidence for its true benefit on breast cancer is still conflicting.  Soy products are popular and considered a healthier option than meats. People have shown some concerns due to its hormonal mimetic estrogenic properties. Natural soy foods which are plant derivatives are full of fibers and essential minerals and nutrients.
Soy contains isoflavinoids, which are similar to estrogen. Several epidemiological studies have shown an association between soy and risk of developing hormone sensitive breast cancer. On the contrary, some argue its anti-estrogenic properties as well. Current research although not consistent, doesn’t support avoiding soy foods as it has other benefits that can lower the cancer risk and recurrence. There are a few studies that have examined the relationship of isoflavinoids on the outcomes of soy before and after the diagnosis of cancer. [20-22] The question is then: if women who are diagnosed with BC should take soy or isoflavinoids or more specifically only women who receive hormonal therapy such a tamoxifen. Several studies conducted in Asian countries provide evidence on the benefit of using isoflavinoids in lowering the mortality and recurrence. [23, 24] The evidence provided by studies conducted in the western countries involving population such as Caucasians, Latinos, and African Americans are still unclear. Zang et al observed that high intake of isoflavones is associated with decrease in all cause mortality in women who didn’t receive hormonal therapy for the estrogen receptor negative tumors.  According to the study, only post diagnosis time period showed inverse relationship with soy intake.
In a study conducted on folic acid intake and breast cancer risk in BRCA mutation carrier suggested a protective role of moderate intake of folic acid and vitamin B12 in BRCA associated breast cancer. Women with daily dietary folate intake between 153 and 400 ?g showed a significant reduction in breast cancer risk compared with those showing daily intake of
Vit D can be taken in many forms including natural foods such as dairy and supplements or through sunlight exposure where 7-deoxycholcalciferol is converted to Vit D. Vit D is then converted to 25 (OH) cholecalciferol that is found in the circulation and the best indicator for vit D status. The inactive form 25(OH) cholecalciferol is converted to an active form as 1-25 di (OH) Vit D. This active form binds to the Vit D receptors of several tissues including breast tissue. In vitro and animal studies have shown its anti-cancer properties through its effects on regulation of cell differentiation, proliferation, and apoptosis.  Vitamin D exists in circulation as 25 (OH) D form and to convert it to its active form 1-25 (OH) D, 1 ?hydroxylase enzyme is needed. Like many other tissues, breast tissues also have 1-?-hydroxylase and converts inactive form of Vit D to active form. Since Calcium and Vit D both have been studied for their regulatory role in estrogen related cell proliferation, it is observed that intake of both nutrients might have different effect on pre and post-menopausal women diagnosed with breast cancer. In a prospective cohort study conducted by Lin et al, it was shown that in pre-menopausal women high intake of vitamin D and calcium was associated with a lower risk of breast cancer more so in more aggressive breast tumors. Additionally, there was no association of Vit D and calcium observed with postmenopausal breast cancer. [27, 28] In a more recent randomized controlled trial, it was shown that another endogenous estrogen receptor modulator, 27 hydroxy cholesterol (HC) has agonistic properties on ER +breast cancer. It was suggested that Vit D supplementation can reduce 27 HC as its inhibition is regulated by Vit D.  So in a nutshell, it can be concluded that Vit D supplements and Vit D can be used to suppress 27 HC mediated ER + breast cancer in high risk patients and have preventive effect on ER+ breast cancer.
Vit D has also been studied for its effect on breast density of premenopausal women. Breast density being the strongest indicator for cancer risk because it masks mammography findings and is estimated to be 4-6 times higher in women with high density. [30, 31] In a double blinded randomized controlled trial, Brisson et al studied the effect of vit D? in the doses of 1000, 2,000, and 3000 IU/day for one year and no reduction was found in breast density in pre-menopausal women.
Carotenoids are considered as micronutrients in our food. The bright orange pigments of carrots, lutein, lycopene, and some others all belong to the carotenoid family. Most of the carotenoids are present in fruits and vegetables readily available as part of our diet. Carotenoids act mostly due to their important antioxidants properties. By neutralizing oxidative processes that can damage DNA and proteins and interfere with the normal functioning of cells, carotenoids have been found to prevent cancer and its progression. Several experimental studies have shown that carotenoids block cancer progression and reduce proliferation of estrogen receptor positive ER+ and ER- breast cancers.  One study conducted at Harvard University (Nurses Health Study), has pooled data from 8 prospective cohort studies including 3055 breast cancer cases with matched controls and concluded that higher total carotenoids, and high concentration of some specific carotenoids such as alpha and beta carotene and lycopene had statistically lower risk of breast cancer and more so in ER negative breast cancer. The study also looked into breast cancer recurrence and mortality and found inverse association with carotenoid concentrations in the blood. In this large study, the Relative Risk for Beta carotene from very highest to lowest concentrations was found to be 0.32 (CI 95% P
High intake of fruits and vegetables combined have shown a possible benefit in the reduction of breast cancer risk. Cruciferous vegetables such a broccoli, cabbage cauliflower and Brussel sprouts contain high content of glucosinolates, and when eaten as raw vegetables, or chewed or in a cut form, an enzyme called myrosinase is released that converts glucosinolates into isothiocyanates. This compound is known for its chemo-protective activity in cancer including breast cancer. The isothiocyantes has differ types that act in different ways. Benzyl isothiocyante induced inhibition is associated with apoptotic cell death. When breast cancer cells were treated with Benzyl Isothyacynate there was an upregulation of proteins ( Bax and Bak) in proapoptotic phase and antiapoptotic protiens (BCL2 ) were down regulated.  The underlying mechanism of isothyacynates seems to be mainly through down regulation of ER and their signaling along with apoptosis and cell cycle arrest thus preventing the metastasis.
Organosulphur compounds such as Indole 3 carbinol, found in many plants derived foods including cruciferous vegetables are also considered beneficial as protect important biomolecules from oxidative damage. In vitro studies have also shown their anti-proliferative activitiy on various cancer cell lines including breast cancer cell lines.
Garlic belongs to the Allium class of plants with bulbs and includes other vegetables as well such as onions, scallions, chives. Garlic is very commonly used in mediterean and asian diets mostly for flavoring. Garlic is considered beneficial due to its high Sulphur content however it has other beneficial contents such as flavonoids, selenium, arginine. Garlic has antibacterial properties and has shown to inhibit the activation of cancer forming substances and enhance DNA repair, reduce cell proliferation, or induce cell death. 
The National Cancer Institute suggests garlic as one of several vegetables with potential anticancer properties and does not recommend the use of other supplements for cancer treatment. The exact amount of garlic that can have protective effect is hard to determine. The active compound present in garlic may lose their effectiveness with time, handling, and processing. The World Health Organization’s guidelines for general health promotion for adults are “a daily dose of 2 to 5 g of fresh garlic (approximately one clove), 0.4 to 1.2 g of dried garlic powder, 2 to 5 mg of garlic oil, 300 to 1,000 mg of garlic extract, or other formulations that are equal to 2 to 5 mg of allicin”.
Curcumin is one of the extensively studied natural products that has been in use for numerous health benefits and many pharmacological effects including anti-proliferation, apoptosis induction, anti-angiogenesis, anti-inflammatory, and as an antioxidant. Its low cost and ability to attack multiple targets in cancer makes it a suitable agent to be explored for cancer management. Curcumin extracted from a plant curcumin longa, has shown inhibitory effect on the proliferation of tumor cells in culture, growth of human tumor cells in xeno-transplant animal models and the same effect was observed when used in combination with chemotherapeutic agents or radiation in animal and rodent models.
The p53 is a tumor suppressor gene involved in many metabolic processes including apoptosis induction, repairing DNA damage, and inducing arrest in cell cycle. Curcumin upregulates p53 expression followed by an increase in p21, that causes arrest at G0, G1 and G2/M phases of the cell cycle and upregulation of Bax expression eventually inducing apoptosis.  More recently, another mechanism known as oncogene induces senescence (OIS) has been gaining attention. The OIS is another tumor suppressing defense mechanism that may be compromised during cancer cell proliferation. The molecular mechanisms and signal transduction pathways for OIS and its role in the p38 mitogen-activated protein kinase (MAPK), the phosphoinositide 3-kinase (PI3K) and Akt8 oncoprotein (AKT) pathways.  The process of OIS was also observed in a breast cancer cell line, where curcumin was shown to inhibit phosphorylation of Akt within the MAPK/PI3K pathway.
Capsaicin found in red chili pepper is also a well-known spice that has shown anti-inflammatory and anti-proliferative activity in breast cancer cells. The suppressive activity of capsaicin was has been observed in several in vivo and in vitro studies. One study conducted on rats showed the suppressive activity of capsaicin against mammary carcinoma that was induced by N-nitrosomethylurea (NMU). Rats treated with NMU and protected with capsaicin improved the histopathological changes in mammary tissues.
Some nutraceuticals have shown their synergistic effect by reducing the side effects and enhancing therapeutic effects by acting on different cell signaling pathways, chemo sensitization, enhancing apoptosis, and inhibition of cell proliferation. For example, a combination of a bioactive compound in soy called genistein and doxorubicin has shown synergistic effects on breast cancer cells by increasing the accumulation of doxorubicin to exert its anticancer effect along with suppressing the expression of HER2. 
Conclusions and Future Perspectives:
Chemoprevention and management through nutraceuticals has become an acceptable strategy. The intake of certain foods and supplements has shown inverse correlation with the risk of breast cancer in several observational and experimental studies. Additionally, several nutraceuticals have shown synergistic activity with chemo and radiotherapy. Some of the most well-known and studied nutraceuticals are carotenoids, citrus fruits, soy foods, vegetables, certain b herbs and spices. Their role in chemoprevention and treatment has been studied extensively while understanding their mechanism of action through different pathways and their role in the inhibition of proliferation, metastasis and angiogenesis in inducing apoptosis and cell cycle arrest. It should be noted that pharmacokinetics, bioavailability and efficacy studies are not that simple to conduct. In order to completely understand their role despite valid data from in vivo and in vitro, more clinical studies are needed to further elucidate their role with established optimal conditions, personalized treatment regimens, stratification based on genotyping and phenotyping, and cost-effectiveness. Also, if more bioactive compounds can be isolated from dietary and natural products to study and understand their mechanism of action, efficacy, toxicity, and adverse effects; these compounds could become the next established potential sources for the prevention and treatment of not just breast cancer but all other cancers and more comprehensive and organized approach is needed for future studies.