Healthy Eating Guidelines For Cancer Prevention: Dietary Supplements


You may be wondering if taking dietary supplements will provide extra protection against cancer. Dietary supplements include vitamin and mineral supplements and other natural health products (such as herbal remedies) taken in addition to the foods you eat.

Steps You Can Take

Choose food as your main source of vitamins, minerals and other cancer fighting compounds, rather than taking dietary supplements for cancer prevention.

Follow the suggestions from "Healthy Eating Guidelines for Cancer Prevention Series: Diet and Cancer Prevention Basics". The benefit of eating a balanced diet with a variety of plant foods for cancer protection is clear. Dietary supplements on the other hand do not protect for certain against cancer for all people nor are they always safe. For a number of reasons, dietary supplements are not routinely recommended for cancer prevention:

  • Disease fighting compounds found in plant foods likely have greater protective health benefits when eaten as whole foods rather than when taken as dietary supplements.
  • Each food is a unique "package" of nutrients. When you take a supplement you are getting only one component of the hundreds of naturally occurring substances that are in whole foods. It is likely that many of the disease fighting compounds in plant foods are not yet identified. We also don't know exactly which components in foods have the most cancer protection.
  • Dietary supplements provide cancer protection for some people but only under specific conditions. For example, in some studies, it is only people who are not getting enough of a nutrient who benefit. If you are eating a well-balanced varied diet then adding more of the nutrient does not necessarily give extra protection.
  • A nutrient may protect against some types of cancer, but may increase risk for other types of cancer. For example, selenium supplements may protect against prostate cancer for people with low selenium levels, but may increase risk for non-melanoma skin cancer.
  • Nutrients may protect at one dosage, but may have unwanted health effects at a slightly higher dose. For example, vitamin E from foods may protect against developing prostate cancer, but vitamin E supplements may increase the risk of developing prostate cancer.
  • Some nutrients may increase cancer risk for specific subsets of the population. For example, high doses of beta-carotene increase risk of lung cancer in smokers.

Take supplements when recommended.

At different life stages, if you have certain medical conditions, or if your food choices are limited, you may need to take specific vitamin and/or mineral supplements or fortified foods for general health. (Fortified foods have vitamins and/or minerals added to them.) For example:

  • Adults over the age of 50 need additional vitamin B12 and vitamin D.
  • Women who may become or are pregnant need folic acid supplements.
  • People who follow a vegan diet or who do not eat foods from all four food groups may need specific vitamin or mineral supplements.
  • Those with food allergies, osteoporosis or other medical conditions may need supplements to fill in gaps in their diets or to provide additional nutrients.

Take supplements cautiously.

  • Unless recommended by your doctor or health professional, do not take individual vitamins and minerals or take big doses of supplements. There is a risk of taking too many vitamins and minerals this way.
  • Although many dietary supplements are believed to be harmless because they are "natural", they may contain vitamins, minerals or other substances in amounts that can cause undesirable and sometimes harmful health effects.
  • When you buy a supplement, always look for a Drug Identification Number (DIN) or Natural Product Number (NPN). These numbers tell you that the supplement meets Health Canada's standards.
  • Be a savvy consumer. Companies who sell supplements may report testimonials or falsely promote products as cancerfighters. "Consumers should be skeptical of health-related products or services that look too good to be true, and should always speak to a health care professional before trying any new treatment" advises the Competition Bureau of Canada.

The bottom line

  • Eat a balanced plant based diet that includes a variety of foods rather than taking dietary supplements to reduce your risk of cancer.
  • Certain people benefit from specific dietary supplements but some dietary supplements may increase cancer risk.
  • For more information about which dietary supplements would be beneficial for you speak with your doctor or a dietitian.

Additional Resources

HealthLinkBC File #68k Vitamin and Mineral Supplements for Adults

Dietitian Services Fact Sheets available by mail (call 8-1-1) or at

American Institute of Cancer Research

Canadian Cancer Society

Information about the Selenium and Vitamin E Cancer Prevention Trial (SELECT)

Last updated: September 2008

These resources are provided as sources of additional information believed to be reliable and accurate at the time of publication and should not be considered an endorsement of any information, service, product or company.

Distributed by:

Dietitian Services at HealthLinkBC (formerly Dial-A-Dietitian), providing free nutrition information and resources for BC residents and health professionals. Go to Healthy Eating or call 8-1-1 (anywhere in BC). Interpreters are available in over 130 languages.

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