Do Antioxidants Lower the Risk of Cancer?

July 12, 2020

by Cathe Friedrich

One reason dietitians recommend eating fruits and vegetables is that they’re high in compounds and chemicals with antioxidant activity. Antioxidants are substances that reduce oxidative stress and the cell and tissue damage it can cause.

Experts believe oxidative stress plays a role in aging and in other diseases, including cancer. Based on this, they believe that consuming more antioxidants is healthy and that doing so could lower the risk of health problems such as cancer. When you read nutritional articles online, they urge you to eat more antioxidant-rich foods for health.

Since antioxidants reduce oxidative stress, the type that damages DNA, you might wonder whether adding more antioxidants to your diet or taking them in supplement form could lower your risk of cancer. What does science say about antioxidants and the risk of cancer?

Evidence for Antioxidants Lowering the Risk of Cancer

In support of the benefits of antioxidants for cancer prevention, researchers at Kimmel Cancer Center made an interesting discovery. In women with breast cancer the researchers found that when they knocked out a gene called Cav-1, the women had a worse prognosis with their cancer.

Cav-1 acts as a tumor suppressor, meaning it suppresses or slows the growth of cancer cells. In fact, when they inactivated this gene, the volume of tumor cells increased by four-fold. Since Cav-1 helps keep tumor growth in check, it’s not surprising that knocking out its activity, worsens breast cancer prognosis.

But what does the Cav-1 gene do? Research shows it reduces oxidative stress and behaves like an internal antioxidant. When you knock it out, tumor cells grow faster, and the tumor becomes larger. So, in the study, antioxidant activity suppressed tumor growth. Not surprising since oxidative stress boosts cancer growth by altering growth pathways and by creating genetic mutations that impact tumor growth.

However, it’s a leap of faith to say that taking antioxidants in supplement form lowers the risk of cancer. In fact, one study found that high doses of antioxidant vitamins, including vitamins C, E, and beta-carotene was linked to a higher incidence of lung cancer growth in smokers. So, it’s not so straightforward.

The Cons of Taking Supplemental Antioxidants

How about other studies? Most observational studies looking at the role of supplemental antioxidants for preventing cancer show mixed results. In fact, nine randomized-controlled trials sponsored by the National Cancer Institute found no benefit of taking antioxidants in supplement form for reducing the risk of cancer.

Even more disturbing, a few studies showed an increase in lung cancer cases and a higher incidence of prostate cancer in people who took antioxidant supplements. A 2011 study of over 35,000 men found that men who took high supplemental doses of vitamin E increased their risk of prostate cancer by 17%.

Food versus Supplements

Most of the studies looking at how antioxidants affect cancer risk were in people who took supplements. Yet research shows eating a diet rich in fruits and vegetables, rich in antioxidants, may modestly lower the risk of some types of cancer. However, we don’t know whether the antioxidants explain the risk reduction or whether it’s other components in fruits and veggies that explain the benefits. Fruits and vegetables are a rich source of a variety of phytochemicals and the benefits may come from the synergy between phytochemicals rather than an isolated antioxidant.

There’s also the concept of the “antioxidant cascade.” Fruits and vegetables contain a variety of antioxidants that work together to reduce oxidative damage. These antioxidants work together in an elaborate cascade whereby one antioxidant donates its electrons to another to preserve the stability of all the antioxidant players. This “teamwork” may explain why antioxidants in food protect while isolated antioxidants in supplement form may not.

It’s More Complicated Than It Seems

Timing may be another factor in how antioxidants impact cancer growth. If you take antioxidants before your cells are damaged, the antioxidants may reduce injury to cellular DNA that could lead to cancer development. However, if you take them after you already have mutations inside cells or when cells are in the early phase of forming a malignancy, antioxidant supplements could spur its growth.

One study also found that when you consume antioxidants in relation to a meal matters. The most beneficial time is after eating a high-fat meal since oxidative stress increases in response to a meal high in fat. Still, your best bet is to choose antioxidant-rich foods over supplements.

The Bottom Line

There’s a lack of evidence that antioxidants in isolated form lower the risk of cancer and some evidence of harm. More compelling is the idea that getting a diverse array of antioxidants in whole food form offers some protection against certain types of cancer. If you’re tempted to buy an antioxidant supplement at the health food store, think twice. A better approach is to stock up on natural sources of antioxidants, like fruits, vegetables, nuts, and spices, and add them to your diet.

Choose lots of green, leafy vegetables and non-starchy veggies in shades of red, yellow, orange, and purple. Color is a marker of antioxidant and anti-inflammatory activity, both of which are important for breast cancer prevention. Season them with flavorful spices, like turmeric, garlic, ginger, and rosemary, to boost their antioxidant and anti-inflammatory benefits even more.

The best way to get antioxidants is the way nature intended, from the foods you eat rather than a bottle of pills. Food packages its antioxidants in the way dictated by nature, the master healer. Plus, you get the added health and nutritional benefits that whole fruits and vegetables offer. Building a diet out of whole, nutrient-dense foods can lower your risk of a number of diseases and health problems. Write a healthy prescription with what you put on your plate!

The take-home message is to consume more antioxidant-rich fruits and vegetables. Changing your diet won’t drop the odds of developing breast cancer to zero but, in combination with other healthy lifestyle habits, it may modestly lower your risk.

References:

Oxid Med Cell Longev. 2017; 2017: 7454031.Published online 2017 May 4. doi: 10.1155/2017/7454031
Eurekalert.org. “Jefferson researchers provide genetic evidence that antioxidants can help treat cancer”
Br J Nutr. 1998 Aug;80 Suppl 1:S77-112. doi: 10.1079/bjn19980106.
CareOncology.com. “Antioxidants and Cancer – Should I take them?”
Integr Cancer Ther. 2004 Dec;3(4):333-41. doi: 10.1177/1534735404270578.
J Breast Cancer. 2013 Jun;16(2):133-137. English. Published online June 28, 2013. https://doi.org/10.4048/jbc.2013.16.2.133.
ScienceDaily.com. “High fruit and vegetable consumption may reduce risk of breast cancer”