Ideally, your body should get all the nutrients it needs from a healthy diet. But sometimes, dietary supplements are necessary.
AICR advises against taking any vitamin, mineral or herbal supplement that isn’t proven to help treat cancer or prevent it from coming back. Here are six supplements you may want to avoid.
Vitamin D
Vitamin D is an important nutrient for many body functions, including bone health and the immune system. It can be found naturally in food and also available as a supplement. A recent study has linked low levels of vitamin D with an increased risk of breast cancer.
The researchers used blood tests to measure serum 25-hydroxyvitamin D, or 25(OH)D. They found that women with high levels of the vitamin had a one-fifth lower risk than those with low 25(OH)D levels. In addition, they found that a deficiency of the vitamin was associated with poorer outcomes in people who had already been diagnosed with the disease. The findings, published March 2 in Endocrinology, suggest that vitamin D may prevent cancer cells from growing and spreading.
However, it’s too soon to tell whether vitamin D supplements can help to prevent or treat breast cancer. Most current research on the topic is based on observations and potential associations, rather than on proven causes and effects.
People who have been diagnosed with breast cancer should speak to their health care team before taking any dietary supplements. They can help people choose a safe and effective supplement that doesn’t interfere with cancer treatments or other health conditions.
Some people are at a higher risk of having low levels of vitamin D due to genetics or lifestyle factors. They can ask their doctor for a simple blood test to determine their level of the vitamin. The recommended level of vitamin D for most adults is 60-70 mg/mL. People who have cancer should talk to their health care provider about having their 25(OH)D levels checked on a regular basis during treatment.
Vitamin C
Vitamin C (ascorbic acid) is an antioxidant that can help lower the levels of free radicals in your body. This can help prevent some cancers, including breast cancer.
Epidemiological studies have shown that women who eat lots of fruits and vegetables that are rich in vitamin C have a lower risk of getting breast cancer. However, these studies are difficult to control for other factors that can affect the results. In addition, taking vitamin C supplements has not been shown to reduce the risk of breast cancer in women who already have the disease.
Animal experiments have found that high doses of vitamin C can cause the death of breast cancer cells. This is thought to be because vitamin C can increase the levels of a protein called TRAIL, which activates apoptosis and decreases the availability of Bcl-xL, which is another protein that blocks apoptosis.
However, vitamin C can interfere with some chemotherapy drugs, so it’s important to talk to your doctor before you take any supplements, especially vitamin C, if you’re being treated for breast cancer or have any other medical condition. High doses of vitamin C can also make certain medications less effective, such as oral contraceptives and hormone replacement therapy.
You should also be careful about using herbal remedies containing vitamin C, because some of them can be harmful. For example, wild ginger (Asarum canadense) contains a substance known as aristolochic acid, which can be toxic to the kidneys. It can also interact with some anticancer medications.
Vitamin E
Vitamin E is a group of fat-soluble antioxidant nutrients with eight natural isoforms. It scavenges reactive oxygen species, prevents lipid peroxidation and protects biological membranes. It also has anticancer effects, including inducing apoptosis in cancer cells and inhibiting carcinogenesis and tumor growth.
Observational studies and animal models have shown that high intakes of vitamins C and E may reduce the risk of cancer. However, when these nutrients were put to the test in placebo-controlled clinical trials, they showed no protective effect. This may be because these supplements are affecting genes in the body that affect how we metabolize these nutrients.
One study found that women who ate more fruits, vegetables and nuts and took multivitamins were at lower risk for breast cancer. While this is interesting, the study was small and only followed a few thousand women over a long period of time. It is not the first study to link multivitamin use with a lower breast cancer risk, and it is important to note that these women are still at risk for other health problems.
If you are taking a supplement, it is important to tell your doctor what you are taking, especially if you need surgery. Some supplements might interact with the medicines used during and after surgery and increase your risk of complications. In addition, some supplements can interfere with how well chemotherapy works by slowing the way your body breaks down these drugs.
Beware of herbal teams such as essiac and laetrile, which is not a vitamin but an herb from the apricot plant that contains a chemical, amygdalin, that turns into cyanide in the stomach. Taking these herbs can make your blood thinner, increasing the risk of bleeding.
Thyroid Supplements
A small number of people with thyroid disorders, such as hyperthyroidism (too much thyroid hormone) or hypothyroidism (too little thyroid hormone), have been linked to a higher breast cancer risk. This risk may be influenced by the severity of the thyroid disorder and the treatments used, such as surgery, antithyroid medications, radioactive iodine treatment or medication to suppress thyroid hormone production.
In a large, population based study, women with a history of thyroid disorders had a slightly elevated risk of breast cancer compared to those without a history of these conditions, regardless of the type of thyroid disorder, age at diagnosis and duration of treatment. The researchers speculate that the increased risk was related to the hormones produced by the thyroid, especially triiodothyronine and thyroxine, which have been shown in in vitro experiments to promote breast cancer growth and angiogenesis in certain cell types.
Folic acid, a form of vitamin B9 found in foods and supplements, has been linked to lower breast cancer risks in postmenopausal women. Folic acid is also a common supplement in many chemotherapy regimens, since it has been found to protect normal cells from damage caused by the chemotherapy drugs and enhance their effect on tumor cells. But it is important to take only the amount prescribed by your doctor, since high doses of folic acid can interfere with your body’s ability to absorb some other vitamins and minerals.
If you are undergoing chemotherapy, it is also important to tell your doctor about any nutritional or herbal supplements that you are taking or plan to use. Some supplements can interfere with the way that chemotherapy works or increase your risk of side effects, including nausea and vomiting. For example, green tea extract can interfere with the drug bortezomid (Velcade), which is used to treat multiple myeloma and some other types of cancers.
Red Clover
Red clover is a common flowering plant that contains phytoestrogens, which are weak plant estrogens. They can interact with estrogen in the body to produce effects similar to those of the stronger endogenous estrogens produced by women. Because of this interaction, there is concern that regular use of red clover may increase breast cancer risk.
However, one study found that regular consumption of red clover isoflavones (Promensil(r) and Rimostil(r)) did not significantly affect the risk of ER positive breast cancer in surgically treated premenopausal patients with oestrogen receptor-positive disease taking tamoxifen. Participants in the study were randomized to take either 40 mg daily of red clover isoflavones or placebo for one year. The researchers analyzed the MRS, BMI and waist and hip circumference of women in the intervention groups, as well as circulating oestrogen levels, insulin resistance, endometrial thickness, mammographic density and bone mineral density. They also analyzed the proliferation of oestrogen-regulated genes in breast cancer cells from women in the treatment group compared to those of the control group.
The results of this study show that a diet high in fruit and vegetables, whole grains, legumes and nuts can help reduce your risk for oestrogen-sensitive tumours and that regular exercise is important. Red clover is not a good alternative to soy-based isoflavone supplements as it can have varying effects on the body because of its interaction with endogenous estrogens.
Taking dietary supplements should only be done under the supervision of your health care provider. Be sure to talk to your doctor about the risks and benefits of any herbal supplements you’re considering, especially those marketed for menopausal symptoms. Supplements like pennyroyal (Mentha pulegium) are known to have hormonal effects and can be harmful to the liver at high doses.
