Chocolate is a rich source of calories and saturated fat, but also has some health-promoting properties. Components of the cacao tree (Theobroma cacao) bean have been shown to have antioxidant, anti-inflammatory, neuroprotective and antimutagenic actions in the laboratory. Generally speaking, dark chocolate, on which we focus in this webpage, has a far higher beneficial micronutrient content than milk chocolate.

Chocolate micronutrients

Dark chocolate (which we define as containing 70-85% cacao solids) is an excellent source of the flavanols catechin and epicatechin, as well as theobromine (which is chemically similar to caffeine) and stearic acid (a saturated fat). Dark chocolate is also a very good source of caffeine and ferulic acid, a good source of fiber, and contains some procyanidins. In addition, dark chocolate has relatively high levels of chromium, copper and iron, and significant levels of magnesium, manganese and zinc.
Like the coffee bean, the cacao bean has a complex and varied chemical makeup. However, chocolate consumption has not been as well studied as coffee consumption and the information concerning its health effects are limited and confounded by the fact that chocolate normally contains sugar and other additives.

Chocolate cardiovascular effects

Unlike other saturated fats, stearic acid does not appear to increase cardiovascular risks. Dark chocolate has been found to significantly improve coronary circulation in healthy adults (it improves endothelial function, decreasing both platelet aggregation and blood pressure). In fact, moderate consumption of dark chocolate appears to exert protective effects against the development of cardiovascular disease. Both milk chocolate and dark chocolate are calorie-dense foods, however consumption of both has been linked to lower risk of stroke and heart attack.

Cacao extracts and cancer

Cacao extracts have been shown to have anticancer activity against human prostate, colon and adrenal cancer cells. A cacao polyphenolic extract has also been found to reduce the incidence of carcinogen-induced prostate tumors in laboratory rats. Stearic acid has been demonstrated to inhibit tumor growth and reduce proliferation of cancer cells in the laboratory. However, consumption of chocolate itself has been found in population studies to be associated with increased risk of stomach, pancreatic and colorectal cancer.

Breast cancer-related effects of eating chocolate

Epidemiological studies

The beneficial effects of individual anticancer compounds in the cacao bean might be difficult to capture by consuming chocolate since it normally is high in sugar and is incorporated into a wide variety of high glycemic index foods. These are not favorable characteristics for breast cancer risk. One Italian study found that consumption of sweet desserts and sugar (including chocolate) was positively associated with the risk of breast cancer, even after adjusting for body mass index.
However, a 2020 prospective study using data from the Women’s Health Initiative Study (with 15-year average follow-up) reported that there was no significant association between chocolate candy intake and risk of invasive breast cancer.
Note that chocolate consumption has been linked to reduced bone density and strength in older women, suggesting that intake should be limited by those under going treatment with aromatase inhibitors, which also tend to reduce bone density.

Cell studies of cacao extracts

Several studies have reported that cacao extracts reduced breast cancer cell proliferation and growth. For example, one study reported that cocoa crude extract induced cell death in two hormone receptor positive (ER+/PR+) breast cancer cell lines without harming normal cells.

Chocolate components with anti-breast cancer effects

Catechins

The most abundant phenolic compounds in cacao extracts are the flavonoids epicatechin and catechin. While green tea's epigallocatechin gallate (EGCG) is the most well-known catechin, chocolate also contains a large fraction of catechins.
Epicatechin and catechin have been shown to induce apoptosis (programmed cell death) in triple negative (ER-/PR-/HER2-) breast cancer cells. One 2021 study reported that epicatechin inhibited triple negative tumor growth as efficiently as Adriamycin (doxorubicin) in an animal model of triple negative breast cancer.
Epicatechin and catechin can be used to build more complex molecules such as proanthocyanidins (which are chains of flavonoids such as flavanols). One study reported that a cocoa-derived procyanidin selectively inhibited the proliferation of ER+/PR+ and triple negative breast cancer cells while sparing normal breast cells.

Ferulic acid

Ferulic acid has been reported to induce programmed cell death in triple negative breast cancer cells. Ferulic acid has also been shown to synergistically enhance the treatment effects of both Taxol (paclitaxel) and epirubicin chemotherapy. In addition, ferulic acid has been found to reduce heart damage caused by Adriamycin in an animal study of Adriamycin-induced cardiomyopathy.

Stearic acid

Stearic acid is a long-chain saturated fatty acid abundant in chocolate. Stearic acid has been shown to inhibit breast cancer cell proliferation, invasion, and migration, and to induce apoptosis in the laboratory. Animal experiments have demonstrated that stearic acid and stearates (salts and esters of stearic acid) can decrease mammary tumor incidence and size.
One study reported that women with high circulating levels of stearic acid had a significantly lower risk of breast cancer than those with lower levels.

Chocolate components that could promote breast cancer

Caffeine

Coffee incorporates more caffeine than chocolate (eight ounces of black coffee contains approximately double the caffeine of two ounces of dark chocolate). However, clearly chocolate's caffeine content can add up, depending on intake. Note that while the theobromine found in chocolate is chemically similar to caffeine, it does not appear to stimulate the central nervous system or share it's potentially harmful effects.
An inverse relationship between caffeine intake and breast cancer has been reported. However, caffeine may have adverse effects for those (1) prone to benign breast disease, particularly atypical hyperplasia, which is associated with increased breast cancer risk; or (2) undergoing treatment with anthracycline chemotherapy.
Relatively high caffeine intake has been found to be associated with hormone receptor negative (ER-/PR-) breast cancer, as well as with breast tumors greater than 2 cm in size, among women with benign breast disease.
Significant chocolate intake might reduce the effectiveness of Adriamycin (doxorubicin) and other anthracycline chemotherapy as a result of its caffeine content.

Copper

While copper does not appear to increase breast cancer risk, it may increase the risk of recurrence. Chocolate, including hot chocolate and chocolate bars, can contain relatively high levels of copper, which could contribute to angiogenesis (the growth of new blood vessels) and metastasis of breast cancer, especially in women with inflammatory breast cancer (IBC) or triple negative (ER-/PR-/HER2-) disease. Dark chocolate contains approximately 0.5 mg per ounce, whereas milk chocolate contains approximately 0.14 mg per ounce. Although copper is a vital nutrient, women with breast cancer probably should not exceed the RDA (recommended daily allowance) of approximately 0.9 mg.

Iron

While it is important to avoid iron deficiency anemia, the contribution of excess iron in the diet as a result of regularly consuming chocolate could be detrimental for some women. Dark chocolate contains approximately 3.37 mg iron per ounce, or 42% of the 8 mg Recommended Dietary Allowance (RDA) for postmenopausal women.
Tumors are iron consumers. Breast cancer cells have abnormal pathways of iron acquisition, storage and regulation, suggesting that reprogramming of iron metabolism is an important aspect of cancer cell survival. Iron has been shown to facilitate cancer cell proliferation, growth, and angiogenesis.
The addition of iron to breast cancer cells and their microenvironment has been demonstrated to protect them from being killed by natural killer cells. At the same time, iron depletion has been shown to lead to significant inhibition of breast cancer cell growth in the laboratory. Relatively high levels of iron in benign breast tissue was found in one prospective study to be associated with increased risk of subsequent breast cancer.
In addition, excess iron has been shown to have the potential to interfere with the treatment effects of the chemotherapy drugs Adriamycin and cisplatin.

The bottom line

Although dark chocolate has a nutrient profile that is in many respects potentially beneficial (assuming it has a low level of sugar), it also has unfavorable properties that should limit intake for those with breast cancer. Based on the available evidence, modest dark chocolate consumption (up to two ounces per day) appears to be safe for most breast cancer patients and survivors. Those with the following circumstances should more sharply limit their chocolate intake:
  • Undergoing treatment with anthracycline (e.g., Adriamycin, Ellence (epirubicin)) or platinum-based (e.g., cisplatin) chemotherapy.
  • With benign breast disease or breast cancer preceded by benign breast disease.
  • Diagnosed with osteopenia or osteoporosis, a family history of osteoporosis, or undergoing aromatase inhibitor treatment.

Additional comments

The highest levels of bioactive cacao compounds are found in products with the highest content of cocoa solids (i.e., cocoa liquor, cocoa powder and dark chocolate), while the lowest levels are found in milk chocolate, white chocolate and chocolate bars. In fact, the milk proteins in milk chocolate may inhibit the absorption of cacao flavonoids. Hot chocolate, with its relatively low cacao content and high milk and sugar content, is not likely to be beneficial with respect to breast cancer risk.
Note that while we are continually searching for new evidence specifically concerning this food, there is not much interest in it among breast cancer researchers, so few studies are available.