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Certain dietary supplements may help reduce the risk of cancer or support the body during cancer therapy. Supplements can contain herbal extracts or vitamins and minerals. There is a large number available, so some people may find it challenging to know where to begin.

However, the term anti-cancer supplements can be a little misleading. Some supplements may help reduce a person's risk of developing cancer or support the body during cancer treatment, but no supplement can replace standard cancer therapies.

Anyone considering taking vitamins and supplements during cancer treatment should seek advice from their doctor first, particularly as some can interact with other medications or cause side effects.

In this article, we discuss some of the dietary supplements that may help prevent cancer or assist in recovery during cancer treatment. We also cover risks and considerations.

a woman taking an omega-3 capsule as an anti-cancer supplement. Share on Pinterest
Research suggests that omega-3 fatty acids might lower a person's risk of developing some types of cancer.

Omega-3s are polyunsaturated fatty acids that are naturally present in a variety of foods, including:

  • fish, including salmon, mackerel, and tuna
  • plants oils, such as those from flaxseed, soybean, and canola
  • nuts and seeds

Some research suggests that omega-3 fatty acids may help prevent some types of cancer.

For example, a 2015 review found some evidence that the anti-inflammatory properties of omega-3s may lower a person's risk of developing breast cancer.

However, a 2019 clinical trial investigated the health benefits of omega-3 fatty acids in 25,871 people.

The researchers found that participants who took omega-3 supplements did not have an overall reduced risk of cancer compared to those who took a placebo. There was also no association between taking omega-3 supplements and a lower risk of breast, colorectal, or prostate cancers.

Dietary supplements that contain omega-3 fatty acids are widely available in health stores and pharmacies in a variety of different forms, including:

  • cod liver oil
  • fish oil
  • krill oil
  • algal oil, which comes from algae and is suitable for vegetarians and vegans

A person can also purchase omega-3 supplements online.

The Office of Dietary Supplements (ODS) recommend a daily intake of 1.1–1.6 grams (g) of omega-3 fatty acids for people aged 14 years and upwards. A person should talk to their doctor before taking omega-3 supplements, as they can interact with some medications.

Green tea is a popular drink that is rich in compounds called polyphenols, which have anti-inflammatory and antioxidant properties. Supplements containing extracts from green tea and its main active component, epigallocatechin-3-gallate (EGCG), may help in the fight against cancer.

According to a 2018 review, EGCG and green tea extracts may help prevent or delay cancer onset, cancer recurrence, and secondary growths from cancer.

However, the National Center for Complementary and Integrative Health (NCCIH) state that studies of green tea and cancer in humans have so far produced inconsistent results.

Drinking one or more cups of green tea each day is a simple way to enjoy its potential health benefits. A person can buy a variety of different green teas online.

Green tea extracts are also readily available as dietary supplements, and people can purchase many of these online as well. However, some may find these extracts to be too concentrated.

According to the NCCIH, green tea can interact with nadolol, which is a medication for treating high blood pressure and heart problems. People currently taking this medication should speak to their doctor before using green tea products.

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Research suggests that garlic and onion may help lower the risk of certain cancers.

Garlic and onions belong to the Allium genus of plants.

According to a 2015 review, eating more of these plants may help lower the risk of certain cancers, particularly in the digestive tract. However, the effect is difficult for researchers to quantify, and it is not clear how much of these vegetables a person needs to eat.

A 2018 study found that garlic extract blocks the growth of some types of cancer cell in test tube experiments and mice models.

However, the researchers also noted that some studies suggest that garlic extract may increase the activity of some chemotherapy drugs. As such, anyone undergoing cancer treatment should talk to their doctor before using garlic extract.

Garlic extract supplements are available to purchase online.

Ginger is a traditional remedy for digestive issues and may also help to relieve the side effects of nausea and vomiting that chemotherapy and radiation therapy can often cause.

Making tea from boiled ginger root or eating natural candied ginger throughout the day may help relieve these side effects. People can also buy a variety of ginger tea online.

Herbal supplements containing ginger extract are also available to purchase online. However, these extracts may be too concentrated for some people.

There is some concern that ginger may interact with blood thinners, so people taking these medications should consult a doctor before adding ginger to their diet.

Turmeric is an orange spice that is a common ingredient in Asian foods, such as curry. Turmeric contains a compound called curcumin, which has both anti-inflammatory and antioxidant properties.

According to a 2016 review, studies suggest that curcumin can slow tumor growth and cause cancer cells to die. However, much of the research is from test tube studies and animal models, and scientists need to carry out more research in humans to confirm the findings.

Both the whole root and the ground spice form of turmeric are widely available in grocery stores. A person can try adding turmeric to curries, rice dishes, soups, and other meals. Turmeric is also available as a tea and a dietary supplement.

A person can buy a range of different turmeric and curcumin products online, including:

Vitamin D is essential for healthy bones, teeth, and muscles and also plays a vital role in the function of nerves and the immune system.

According to the National Cancer Institute (NCI), research in mice indicates that vitamin D may slow or prevent the growth or development of cancer. The NCI also note that some studies in humans suggest that higher intakes of vitamin D may lower the risk of certain types of cancer. However, the results so far have been inconsistent, and scientists need to carry out more research.

The ODS recommend a daily intake of 600 international units (IU) or 15 micrograms (mcg) of vitamin D for most people.

Many people can get enough vitamin D from sun exposure. The body naturally produces vitamin D when the skin becomes directly exposed to sunlight.

Vitamin D is also present in a limited number of foods, including:

  • oily fish, such as salmon, mackerel, sardines, and tuna
  • red meat and liver
  • mushrooms
  • cheese and egg yolks
  • fortified foods, such as certain breakfast cereals, orange juices, and milk

Vitamin D supplements are available in two forms:

  • vitamin D2, or ergocalciferol
  • vitamin D3, or cholecalciferol

Both of these forms increase vitamin D levels in the body in a similar manner. A person can buy vitamin D supplements online.

Antioxidants counteract free radicals in the body, which may help protect against oxidative stress and cellular damage. Oxidative stress may play a role in the development of cancer and some other diseases.

However, the NCI report that clinical trials to date have not provided evidence that taking antioxidant supplements can lower a person's risk of developing cancer. They also point out that some studies suggest that antioxidant supplements may worsen outcomes during cancer treatment, particularly in people who smoke.

Other studies in mice with tumors also found that antioxidants can promote tumor growth and metastasis, which is when cancer spreads to other parts of the body.

The NCI recommend that people undergoing cancer treatment speak to the doctor before taking antioxidant supplements.

A range of antioxidant supplements are widely available in health stores and pharmacies, and people can also buy them online. Examples include:

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A person should speak to their doctor about any interactions that a supplement might have with their other medications.

While doctors consider dietary supplements to be generally safe, some may cause side effects or interact with medications. People who are considering taking a dietary supplement should speak to their doctor first, particularly if they are currently taking any medications.

The Food and Drugs Administration (FDA) do not regulate dietary supplements as strictly as they regulate medications and do not routinely monitor them for quality, consistency, or safety. This means that it is essential that people purchase dietary supplements from reputable manufacturers.

Some herbal extract and vitamin supplements may help lower the risk of cancer or support the body during cancer therapy.

However, it is important to note that the scientific evidence for many of these supplements is limited or inconsistent. Also, dietary supplements cannot replace standard cancer therapies.

While dietary supplements are generally safe, some can cause side effects or interact with certain medications, including cancer drugs. It is, therefore, advisable to speak to a doctor before taking a dietary supplement, particularly people who are undergoing cancer treatment.

The FDA do not regulate dietary supplements in the same way that they regulate foods and drugs, so the quality and consistency of supplements can vary. People should only buy dietary supplements from reputable manufacturers.