Sunflower (Helianthus annuus) oil ranks fourth in world vegetable oil production, after palm oil, soybean oil and canola oil. Sunflower oil (i.e., sunflower seed oil) is an abundant dietary source of unsaturated fat, primarily the polyunsaturated omega-6 fatty acid, linoleic acid (59% to 71% of total fat). It is also a good source of vitamin E.
Sunflower seeds have been shown to have antioxidant activities and are a very good source of selenium, vitamin E and several B vitamins. However, the seeds are also a dietary source of exposure to heavy metals such as the breast carcinogen cadmium.
Breast cancer-related effects of consuming sunflower oil
Complex relationship between fats and breast cancer
The relationships between oil and fat consumption and breast cancer are complex and appear to depend on the specific attributes of the oil or fat in question. It was originally thought that consumption of fat promoted breast cancer, regardless of the source of fat. The focus then shifted to saturated versus unsaturated fat, with further refinements concerning monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs).
More recently, the emphasis has shifted to the balance between omega-6 and omega-3 fatty acids in the diet. The reason for these changes in emphasis is that none of the theories were found to hold consistently in population studies. While the theory that cancer is caused in part by an excess of omega-6 fatty acids in the Western diet appears to be valid, it is not a global explanation for the relationship between oils and fats and breast cancer. For example, it does not explain the fact that olive oil, which does not have a high omega-3 content, is protective against breast cancer.
In the case of sunflower oil, both the oil and its primary omega-3 fatty acid, linoleic acid, have been linked to increased breast cancer risk in human, animal and cell studies.
Human studies
Women with breast cancer have been found to have higher levels of omega-6 fats in their breast tissue than similar women without breast cancer. Several studies have found that lower dietary omega-6/omega-3 ratios are associated with reduced risk of breast cancer. Consuming sunflower oil would tend to increase the ratio for most women because of its high omega-6 content.
One study reported that women with a specific genotype (ALOX5AP −4900 A > G polymorphism) who consumed a significant amount of linoleic acid in their diets had an increased risk of breast cancer. Another study found increased breast cancer risk among women cooking primarily with high linoleic acid vegetable oils compared to women using olive oil or canola oil.
Animal studies
While animal studies regarding sunflower oil are uncommon, numerous studies have been performed with diets high in corn oil (another high-linoleic acid oil) or arachidonic acid in mice or rats bearing either carcinogen-induced tumors or transplanted mammary tumors. Such diets were found to stimulate the formation and growth of breast tumors in the animals.
Daughter mice of female mice fed a high linoleic acid diet were also more prone to develop mammary tumors in one experiment.
Cell studies
Linoleic acid has been reported to promote migration, invasion and angiogenesis of triple negative (ER-/PR-/HER2-) breast cancer cells in several studies.
Insulin is a hormone well known to be involved in the metabolism of carbohydrates. However, insulin is also a growth factor that can stimulate cell proliferation and migration. High circulating insulin levels such as those typical of type 2 diabetes have been shown to increase the risk of breast cancer and its recurrence. Linoleic acid has been shown to amplify the deleterious responses to insulin in both ER+/PR+ and triple negative breast cancer cells.
Sunflower seeds are a dietary source of cadmium and copper
Sunflower seeds grown for consumption as seeds are known as confectionary sunflower seeds. Of the products typically consumed as snack foods, pistachio and sunflower kernels are the richest in phytosterols, which can help lower cholesterol. Sunflower seeds are also a good dietary source of selenium and the lignan enterolactone, both of which are associated with reduced risk of breast cancer. However, as noted above, sunflower plants have a tendency to accumulate heavy metals, and the seeds and kernels can contain significant levels of iron, cadmium and copper.
Cadmium
U.S. confectionary sunflower seeds are grown primarily in North and South Dakota, a region with relatively high cadmium levels in the soil. Stricter European rules on cadmium in sunflower imports from the U.S. have caused confectionary sunflower seeds grown in U.S. soils with lower levels of cadmium to be diverted to the European market. Efforts have been under way for several years to breed sunflower hybrids that will take up less cadmium, however it is not clear to what extent U.S. consumers are benefiting from such efforts. For more information regarding cadmium and breast cancer, please see cadmium increases breast cancer risk.
Copper
Sunflower seeds contain approximately 0.51 mg copper per ounce. Copper has been shown to promote angiogenesis and metastasis, especially in aggressive forms of breast cancer such as inflammatory (IBC), triple negative, and HER2 overexpressing (HER2+) breast cancer.
Although copper is a vital nutrient, women with breast cancer probably should not exceed the RDA (recommended dietary allowance) of approximately 0.9 mg. High copper foods such as calf's liver and beef liver should be avoided. Foods with moderate copper content, such as shellfish, textured soy protein, chocolate, most tree nuts, and sunflower seeds also should be limited or avoided. Copper consumption should be reserved for foods such as walnuts, which contain approximately 0.45 mg copper per ounce, but have exceptional anti-breast cancer properties.
Additional comments
As noted above, the breast cancer-linoleic acid connection is not straightforward. Omega-6 fats are essential to health and the ratio of omega-6 to omega-3 fats (such as the docosahexaenoic acid (DHA) found in fatty fish) appears to be more important than the absolute amounts of these fatty acids in the diet.
Dietary sources of linoleic acid
Below are common cooking oils with high levels of linoleic acid as a percentage of total fat content:
| Cooking oil | Linoleic acid |
|---|---|
| Safflower oil | 75% to 82% |
| Sunflower oil | 59% to 71% |
| Corn oil | 52% to 62% |
| Soybean oil | 51% to 56% |
Better choices are olive oil (7% to 15% linoleic acid) or canola oil (19% to 26%).
Sources of information provided in this webpage
The information above, which is updated continually as new research becomes available, has been developed based solely on the results of academic studies. Clicking on any of the underlined terms will take you to its tag or webpage, which contain more extensive information.
Below are links to 20 recent studies concerning this food and its components. For a more complete list, including less recent studies, please click on sunflower oil.