By pumpkin (Cucurbita pepo), we mean common pumpkins, as well as smaller members of the pumpkin family with orange or deep yellow flesh. This includes butternut squash, acorn squash, winter squash, spaghetti squash, harlequin squash, Hokkaido pumpkins, red kuri squash, and other orange- or yellow-fleshed winter squashes.
Pumpkins are an excellent source of the carotenoids alpha-carotene, beta-carotene and beta-cryptoxanthin (all of which are converted in the body to vitamin A), as well as some lutein. Butternut squash has particularly high carotenoid content (higher than common pumpkin). In addition to carotenoids, pumpkins are a relatively good source of a variety of cucurbitacins (most importantly, cucurbitacin B and cucurbitacin E).
Pumpkin seeds also contain significant levels of copper, iron, magnesium, manganese, and zinc, and some vitamin E and enterolactone. The major fatty acids in pumpkin seeds are oleic acid, linoleic acid and palmitic acid.
Pumpkin consumption is associated with reduced breast cancer risk. Pumpkins are a source of a variety of compounds with anti-cancer activities.
Most of the population-based breast cancer studies performed to date that specifically include pumpkins have been conducted in Japan (where pumpkin consumption is relatively high). One Japanese study found that consuming vegetables (specifically including pumpkins) reduced the risk of breast, lung, gastric and colorectal cancer, regardless of the family history of cancer. Another Japanese study found reductions in breast cancer risk associated with high intakes of green-yellow vegetables (including green leafy vegetables, carrots and pumpkins) among both premenopausal and postmenopausal women.
Overall impact on breast cancer
Women with substantial intake of carotenoids, such as the alpha-carotene, beta-carotene, beta-cryptoxanthin and lutein found in pumpkins, have been reported to have lower overall risks of breast cancer and its recurrence in numerous studies. However, not every study concerning carotenoids and breast cancer has reported such links.
Specific chemopreventive actions of carotenoids
Consuming foods high in carotenoids has been shown to reduce the risk of breast cancer among women with high breast density (itself a strong risk factor for breast cancer). A Scandinavian study found that dietary (but not supplemental) beta-carotene had a protective effect against lobular breast cancer in postmenopausal women. Another European study reported that high intake of beta-carotene was protective against breast cancer in postmenopausal women using hormone replacement therapy (HRT). The same study also found that dietary beta-carotene was associated with lowered risk of breast cancer in postmenopausal women with relatively high alcohol consumption.
High circulating beta-cryptoxanthin has been shown to be associated with lower risk of benign breast disease or breast carcinoma in situ (DCIS or LCIS) in premenopausal women.
In addition, higher levels of carotenoids and vitamin A (retinol) in the blood of breast cancer survivors have both been found to be associated with greater likelihood of breast cancer-free survival.
Breast cancer treatment
Beta-carotene has been reported to enhance the cytotoxicity of Adriamycin (doxorubicin) in both hormone receptor positive (ER+/PR+) and triple negative (ER-/PR-/HER2-) breast cancer cells. Beta-carotene has also been demonstrated to reduce multidrug resistance in cancer cells.
Carotenoid supplements are not recommended
Carotenoid supplements are not recommended. Frequent use of combination multiple carotenoids has been found to be associated with increased risk of breast cancer-specific mortality.
Cucurbitacin B and cucurbitacin E are bitter compounds found in modest amounts in pumpkins, zucchini and some other foods. These foods have been cultivated to minimize their cucurbitacin content and the associated bitterness and toxicity. Cucurbitacins are not destroyed by cooking.
Cucurbitacin B
Cucurbitacin B has been shown to inhibit the growth and proliferation of ER+/PR+, HER2+ and triple negative cells, as well as cells with BRCA1 mutations. A tiny amount of cucurbitacin B was found to halve tumor volume without harming the animals in an experiment using a mouse model of triple negative breast cancer.
A low dose of cucurbitacin B was also shown to enhance the treatment effects of Taxotere (docetaxel) in another mouse model of triple negative breast cancer, without toxicity to the animals.
Cucurbitacin E
Cucurbitacin E has been shown to induce cell cycle arrest and apoptosis in ER+/PR+ and triple negative breast cancer cells. In addition, cucurbitacin E has been demonstrated to reduce metastasis by inhibiting cell migration and invasion in a mouse model of triple negative breast cancer.
There is some evidence that cucurbitacin E can improve treatment of multidrug-resistant breast cancer cells by targeting EGFR and silencing its downstream signaling paths. In fact, cucurbitacin E has been reported to increase the treatment effects of Adriamycin in ovarian cancer cells.
Bitter Cucurbitaceae
Colocynth (Citrullus colocynthis), also known as bitter apple or bitter cucumber, and bitter Hawkesbury watermelon (Citrullus lanatus), which are both related to watermelon, have a much higher fraction of cucurbitacins than pumpkins or any other food. High-cucurbitacin extracts of these inedible fruits are sometimes sold as herbal remedies, including for cancer. However, while chemotherapy based on cucurbitacins may eventually be developed, these are toxic chemicals whose safety profiles and appropriate dosages have not been determined. Cucurbitacin supplements are not recommended.
Pumpkin seeds have both favorable and unfavorable breast cancer-related characteristics, suggesting that their consumption should be limited. As noted above, pumpkin seeds are a source of the phytoestrogen enterolactone, which has been reported to reduce the risk of breast cancer recurrence and death among postmenopausal women, especially those with ER- breast cancer. Enterolactone has also been found to increase the sensitivity of breast cancer cells to radiation, thereby potentially enhancing the treatment effects of radiotherapy.
One German study reported that relatively high consumption of pumpkin seeds was associated with reduced breast cancer risk compared to no consumption. However, pumpkin seeds can also be a concentrated source of harmful heavy metals such as lead, depending on where the pumpkins are grown. German regulations are much stricter in this respect than U.S. regulations. Most pumpkin seeds sold in the U.S. are imported from China, which is known for heavy metal pollution in some regions. Therefore, consumers of pumpkin seeds should make sure that the seeds are of high quality.
Even assuming U.S. grown, organic pumpkin seeds, their consumption should be limited. Pumpkin seeds are a source of copper (approximately 0.4 mg per ounce), although its potential effects are offset to some extent by the zinc content of the seeds (since zinc competes with copper for absorption into the body). Copper can promote angiogenesis and metastasis of breast cancer. While copper is a vital nutrient, women with breast cancer should not exceed the RDA (recommended daily allowance) of approximately 0.9 mg. In addition, while low circulating zinc levels are associated with increased breast cancer risk, it has not been established whether high levels of zinc promotes or prevents breast cancer.
Consumption of pumpkin seed oil should also be limited. Unrefined and cold pressed pumpkin seed oils contain more beneficial micronutrients (including cucurbitacins, which are present in the seeds) than highly refined oil, but are also more likely to be contaminated.
The phytoestrogen content of pumpkin seed oil appears to confer estrogenic activities that have the potential to promote ER+ breast cancer. One study found that pumpkin seed oil supplementation prevented changes in plasma lipids and blood pressure associated with inadequate estrogen availability in experimental rats that had their ovaries removed. Another study reported that women who received pumpkin seed oil experienced significant improvements in menopausal symptoms compared to a control group who received wheat germ oil, which is suggestive of pumpkin seed oil's estrogenic properties.
Pumpkins (whether store bought or home grown) with an unusually bitter taste, which indicates that they may have an abnormally high level of cucurbitacins, should be avoided.
Pumpkin flesh and seeds should be eaten cooked or roasted, not raw. One study found that raw pumpkin juice increased chromosomal damage in bone marrow cells of experimental rats treated with a carcinogen whereas boiled pumpkin juice significantly suppressed it. Pumpkin seed oil spoils easily and must be refrigerated or stored in a cool, dark place.
Below are links to recent studies concerning this food and its components. For a more complete list of studies, please click on pumpkin.