5 supplements you shouldn't take to prevent cancer, according to a dietitian

Taking excessively high doses of some vitamins and minerals can backfire—or be a complete waste of your time (and money).

Key Points

• Dietary supplements shouldn't be taken to reduce your cancer risk.
• Experts encourage getting nutrients from foods like fruit, veggies and whole grains instead.
• Consider lifestyle changes like limiting alcohol and getting regular exercise to lower risk.

If there's one thing to know about supplements and cancer prevention, it's this: There's no evidence that taking a supplement can prevent cancer. In fact, the World Cancer Research Fund (WCRF) recommends meeting nutrient needs through food rather than relying on supplements for cancer prevention. "Overwhelmingly, studies on supplements rarely pan out," says Hillary Wright, M.Ed., RD, a senior oncology dietitian. While supplements can play an important role in certain situations—such as correcting a nutrient deficiency—they haven't been shown to reduce cancer risk in otherwise healthy people, explains Wright. 

Still, it's easy to see the appeal. "It can be easier to take a pill than think about how to incorporate more fruits and vegetables into your diet," says Wright. Ahead, we take a closer look at five supplements that have been touted for cancer prevention—and what the research actually says.

1. Beta Carotene

Beta carotene is an antioxidant plant pigment that belongs to the carotenoid family. Your body converts beta carotene into vitamin A, and it's found in foods like carrots, dark leafy greens, sweet potatoes and cantaloupe.

"The interest in beta carotene came from the observation that people who eat more fruits and vegetables seem to get less lung cancer. However, beta carotene is one singular component of countless compounds that someone's body is exposed to if they eat more fruits and vegetables," Wright explains. 

In previous research on beta carotene supplements, researchers found that people who smoke and take beta carotene supplements have a higher risk of lung cancer, and some of the research was stopped early because of the findings, she says. Wright adds, "From a nutritionist standpoint, it's not surprising that when we cherry-pick a particular nutrient and take it in high doses that don't occur in nature, there may be unintended consequences."

2. Vitamin C

Vitamin C is another antioxidant vitamin that has long been associated with immune system support. "There's been an interest in vitamin C 'boosting' the immune system for decades. I haven't read any science that backs that up across the board," says Wright. "There is a lack of evidence suggesting that we should take daily supplemental vitamin C."

Unlike beta carotene, which is converted into the fat-soluble vitamin A and can accumulate in the body, vitamin C is a water-soluble vitamin. That means your body doesn't store large amounts of it, and any excess is typically excreted in urine. As a result, it generally poses less of a safety concern than supplements such as beta carotene.

That said, eating foods rich in vitamin C is still a smart choice. In fact, diets high in vitamin C-rich foods have been associated with a lower incidence of several cancers, including breast, cervical, endometrial, esophageal, lung, pancreatic and prostate cancer.

3. Vitamin E

Like beta carotene, vitamin E supplements may cause more problems than they solve. Because vitamin E is an antioxidant, researchers have long been interested in whether it might help prevent cancer. However, studies examining vitamin E supplements and cancer risk have produced mixed results.

Unfortunately, there is not enough evidence to support taking vitamin E supplements for cancer prevention. In fact, some research suggests that high-dose vitamin E supplements may increase the risk of certain cancers, particularly prostate cancer.

4. Vitamin D

Vitamin D acts like a hormone in the body, helping to improve calcium absorption and support bone health. We get vitamin D from certain foods, such as fortified dairy products, and our skin produces vitamin D in response to sunlight exposure. There's no doubt that getting enough vitamin D is incredibly important for overall health. "We have vitamin D receptors in almost every cell in our body—but this doesn't mean that people need to be super vitamin D'd," says Wright. 

When it comes to cancer, some studies suggest that vitamin D may help inhibit the growth of cancer cells. However, there is not enough evidence to show that taking vitamin D supplements reduces cancer risk in humans.

If you suspect your vitamin D levels are low—a common occurrence during the winter months, especially in northern climates—talk with your health care provider about getting tested and whether a supplement may be appropriate for you.

5. Calcium

Calcium is a key nutrient for bone health, muscle and nerve function, and blood clotting. In some cases, your health care provider may recommend a calcium supplement if you're at risk for deficiency due to your health status or dietary intake.

However, research suggests that consuming more than 1,000 milligrams of calcium from supplements per day is associated with a 53% higher risk of cancer mortality. (Calcium from food was not associated with this increased risk.) Researchers don't yet know exactly why excess supplemental calcium may have this effect, but it's possible that calcium from supplements is absorbed and processed differently than calcium naturally found in foods.

Other Strategies to Reduce Cancer Risk

Overall, cancer prevention isn't found in a pill. "Overwhelmingly, diet and lifestyle strategies show the most promise for reducing cancer risk and supporting survivorship," says Wright. According to the WCRF, about 40% of cancer cases may be preventable. Here are five evidence-based strategies the organization recommends to lower your risk:

• Maintain a healthy weight. Excess body weight is associated with chronic inflammation and hormonal changes that can increase cancer risk.
• Engage in physical activity. Regular exercise helps support overall health and weight management. Adults should aim for at least 150 minutes of moderate-intensity activity each week.
• Eat a balanced diet. A diet that consists of whole grains, fruits, vegetables and beans is ideal. These foods provide fiber, vitamins, minerals and beneficial plant compounds that may help protect against cancer.
• Limit red and processed meats, fast foods and sugary drinks. Diets high in these foods have been linked to an increased risk of certain cancers, particularly colorectal cancer.
• Limit alcohol and avoid smoking. Alcohol increases the risk of several cancers, while smoking remains the leading cause of lung cancer and contributes to many other types of cancer.

One more recommendation from the WCRF? Don't rely on supplements to prevent cancer. Instead, focus on the lifestyle habits that have consistently been shown to support long-term health.

Our Expert Take

Dietary supplements should not be relied upon to reduce cancer risk. While many supplements have not been shown to prevent cancer, some may even increase the risk of certain cancers when taken in high doses—particularly antioxidant supplements such as beta carotene. Instead of looking to supplements for protection, focus on the lifestyle habits that have consistently been linked with lower cancer risk, including maintaining a healthy weight, staying physically active and eating a balanced diet rich in whole grains, fruits, vegetables and legumes. If you need a supplement because of a health condition, nutrient deficiency or dietary restriction, follow your health care provider's recommendations.

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