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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Sunshine, Tea and Tomatoes: Can They Prevent Cancer?

December 19, 2010

Reviewed by the Faculty of Harvard Medical School
Food For Thought Food for Thought

Sunshine, Tea and Tomatoes: Can They Prevent Cancer?

Last reviewed and revised by Faculty of Harvard Medical School on December 19, 2010

By Stacy Kennedy, M.P.H., R.D., L.D.N.
Brigham and Women's Hospital

News media often report on research studies about aspects of foods that may help keep cancer at bay. The dietary supplement industry is also quick to promote new products with promising research in the fight against cancer. With so much information available, it's important to find reliable recommendations and sources you can trust.

This article will discuss practical tips for improving your diet to help ward off cancer or strengthen your resilience against its effects based on the latest research. We'll also provide you with guidance on where you can find trustworthy information about nutrition and cancer.

Vitamin D

Vitamin D has received a lot of press for its potential cancer-fighting capabilities. Many studies have shown that adequate vitamin D intake has been associated with a reduced risk of colon, breast, prostate and ovarian cancers. Yet many Americans are vitamin D deficient.

Our primary source of vitamin D is our daily exposure to UVB sunlight. We get only small amounts of vitamin D from foods such as fortified dairy products. For those living above the 37th latitude, such as in the northeastern United States, sun exposure is inadequate during the late fall and winter to convert vitamin D in the skin to its active form. This is especially true for people with darker skin.

The Recommended Dietary Allowance (RDA) for vitamin D is 600 International Units (IU) for adults under 70 years old and 800 IU for people over 70. Some experts recommend a higher dose of 1,000 IU daily. This level is safe, but may be hard to obtain from diet alone. A person would need three cups of fortified milk as well as one serving of fatty fish each day.

Vitamin D supplements are inexpensive and safe in doses of less than 2,000 IU. The cost of taking 1,000 IU of Vitamin D3, the more desirable form, is less than five cents per day. Always speak with your doctor before beginning a new vitamin regimen.

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Lycopene is one of the more popular carotenoids, second only to beta-carotene. Lycopene is the phytonutrient found in deep red or orange plant foods, such as tomato products. Phytonutrients are naturally occurring plant compounds that are known to benefit human health in a variety of ways, such as supporting the immune system or acting as antioxidants.

Consumption of lycopene, especially in cooked tomato products, has been associated with a reduced risk of prostate cancer. Research has shown that men who consume cooked tomatoes two to four times a week had a 33% lower risk of prostate cancer than those who ate no cooked tomatoes. Recent studies, however, show conflicting results regarding the effectiveness of this nutrient in preventing prostate cancer.

Lycopene works by acting as an antioxidant, a substance that can destroy toxic molecules called free radicals that cause cell damage. Lycopene also enhances cell-to-cell communication. In order for lycopene to be adequately absorbed, the tomato should be cooked and consumed with some healthy fat, since lycopene is a fat-soluble nutrient. Possible combinations include tomato sauce containing olive oil on whole-wheat pasta, tomato soup made with low-fat milk, or a stir-fry in extra virgin olive oil with diced tomatoes.

Tomatoes have other ingredients that also may help prevent cancer and boost the immune system. They are good sources of folate, vitamin C, vitamin A and vitamin E, as well as other carotenoids and phytonutrients such as polyphenols.

It's possible that lycopene acts in concert with the other phytonutrients found in tomatoes to provide its anti-cancer benefits. Our tendency to combine tomatoes with additional fruits and vegetables may be an important reason for the positive health effects.

Lycopene taken in pill form does not appear to reduce prostate cancer risk. The lycopene needs to be from food. Research suggests that the right amount of lycopene in the diet is at least 30 milligrams daily, which is approximately:

  • ½ T. tomato paste
  • ¾ C. tomato sauce
  • 1½ C. (12 fluid ounces) tomato juice

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Green Tea

Green tea is very popular as a drink or supplement and is touted as a potent anti-cancer elixir from Asia. Some studies from China indicate that regular green tea drinkers have a lower risk of prostate cancer as well as lower risk of death from ovarian cancer. However, other studies have been inconclusive about the effects of green tea on cancer prevention or survival.

In laboratory studies and some animal studies, green tea appears to help prevent cell mutations and tumor growth. It also appears to enhance the action of chemotherapy to kill some types of cancer cells. However, studies of green tea supplements in humans with cancer have had disappointing results. The patients have not shown any significant cancer regression and the side effects can be significant. Side effects of the supplements include nausea, vomiting, insomnia, fatigue, diarrhea, abdominal pain and confusion.

Drinking green tea and taking supplements of green tea or tea extracts are very different. Drinking a few cups of green tea each day is not harmful. However, green tea supplements are not recommended.

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Reliable Sources of Information

The research on nutrition and dietary supplements is growing rapidly. It's important to find reliable information to help you make decisions. In addition to this website, here are some good online resources available to the public:

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Stacy Kennedy, M.P.H., R.D., L.D.N., C.N.S.D., is senior clinical dietician at Dana-Farber Cancer Care/Brigham and Women's Hospital. She completed her dietetic internship at Massachusetts General Hospital and received her Master of Public Health in Nutrition from the University of North Carolina.

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