Dietary Antioxidants and Lung Cancer Risk

Dietary Antioxidants and Lung Cancer Risk

Review of Am J Epidemiol. 2004;160(1):68-76.

The most important risk factor for lung cancer is cigarette (tobacco) smoking. However, even for individuals who currently smoke or have a history of smoking, certain types of diet may increase or decrease lung cancer risk. A study in the American Journal of Epidemiology looked at the connection between dietary antioxidants (antioxidants from food) and risk of lung cancer in smokers. This study found that people who ate a diet highest in a combination of antioxidants that included carotenes, flavonoids, vitamin E, selenium and vitamin C had the lowest risk of lung cancer. We provide PRACTICAL information on what these findings mean. We discuss which foods are the best sources of these nutrients and how you can get more of these foods into your diet. Factors such as past history of smoking, age, and gender cannot be changed, but diet and nutrition can. Along with quitting smoking, this type of information will allow people to take concrete and practical steps that may decrease their risk of lung cancer.

Note: Numbers appearing at the end of sentences indicate research references. References are listed at the end of each article.

Background

The most important risk factor for lung cancer is cigarette (tobacco) smoking (1). However, even for individuals who currently smoke or have a history of smoking, diet and nutrition may increase or decrease lung cancer risk (2-36). Now researchers are interested in determining which specific foods and nutrients might best protect against lung cancer. A study published in the American Journal of Epidemiology looked at dietary antioxidants (antioxidants from food) and risk of lung cancer in smokers (37). It is hoped this type of research will identify specific dietary factors that increase or decrease lung cancer risk. Factors such as past use of cigarettes, age, and genetics cannot be changed, but diet and nutrition can! Along with quitting smoking, this type of information will allow people to take concrete and practical steps that may decrease their risk of lung cancer.

What The Researchers Studied

For this study (37), the researchers used diet and nutrition information that was collected previously as part of a large clinical trial on possible cancer-preventive benefits of beta-carotene and vitamin E supplements in smokers (36). This original clinical trial did not show benefit to male smokers who used beta-carotene and/or vitamin E supplements. It even suggested that in smokers, taking these supplements may cause more harm than good (36). 

For the current study (37), the researchers used the diet information from the original 27,111 men who participated in the clinical trial. They created a "dietary antioxidant index" by adding together the different antioxidants that these men were eating from food sources (not pills). The dietary antioxidant index included food sources of carotenes, flavonoids, vitamin E, selenium and vitamin C. Carotenes and flavonoids, which are sometimes referred to as phytochemicals, are found in many different types of fruits and vegetables. Information on other important lifestyle factors including age, height and weight, number of cigarettes smoked per day, alcohol use, and whether or not the men received dietary supplements as part of the original clinical trial was collected and accounted for in the study.

The researchers looked at all of the lung cancer cases that had occurred in this group of men since the original clinical trial, approximately fifteen years earlier. They wanted to determine if diet and nutrition, specifically the dietary antioxidant index, was related to which of these men later developed lung cancer.

What The Study Found

First, the researchers found that men who had the highest score on a dietary antioxidant index that included food sources of carotenes, flavonoids, vitamin E, selenium and vitamin C had a significantly lower risk of lung cancer when compared to men who scored lowest on the dietary antioxidant index. In other words, the men who ate the most antioxidants from food were less likely to be diagnosed with lung cancer than men who ate the least of these food nutrients.

Second, the researchers found similar results when they looked at the overall amounts of fruit and vegetables that the men in this study were eating. In other words, the men eating the most fruit and vegetables had significantly lower risk of lung cancer when compared to men eating the least of these foods. In this study, men eating the most fruit and vegetables ate about 2 to 3 servings of these foods per day, while men eating the least fruit and vegetables ate less than one serving per day.

For reference, a serving of fruit is:

• 1 medium apple, banana, or orange
• 1 melon wedge
• 1/4 to 1/2 cup berries or chopped fruit
• 1 to 2 oz dried fruit (a small handful)

A serving of vegetables is:

• 1 cup, loosely packed raw green leafy vegetables or 1/2 cup cooked greens
• 1/2 cup chopped any other vegetable, cooked
• A handful of baby carrots (5-7)
• 6 oz vegetable juice

What do these results mean?

If the men in this study are similar to most people who regularly smoke, then this study suggests that eating more antioxidants from foods may significantly decrease risk of lung cancer. It is important to note that the researchers were studying antioxidants from FOOD sources, not dietary supplement pills.

However, before we decide what these results mean, it is important to consider some of the limitations and weaknesses of this type of study.

This study was conducted in Finland and the results of this study may or may not apply to people living in countries other than Finland. There may be differences in other health factors between Finnish and non-Finnish people. We don't know if researchers would find the same results if they were studying other groups of people.

Also, the researchers used diet and nutrition information that the men reported at the beginning of the study, 15 years earlier. This does not account for the fact that a person's diet can change quite a bit over the years.

This type of research cannot prove cause and effect. The study only tells us that there is an association between eating more antioxidant-rich foods and later being diagnosed with lung cancer. It is important to remember that an association is not causation (cause and effect). There are other factors that could account for or explain the results of the study.

On a positive note, the results of this study agree with other research telling us that vegetables, fruit, and the nutrients that are found in these foods may reduce risk of lung cancer (9,20,31).

In summary, despite some weaknesses of the study reviewed (37), it fits well with what we know about diet and lung cancer risk. More importantly, there are NO downsides to improving diet and eating healthy!

How can I change my diet to lower my risk of lung cancer?

Remember, most importantly, stop smoking if you currently have this habit. This is the single best way to reduce risk of lung and many other types of cancer. In addition to this, eating more foods that contain a wide variety of antioxidants may be helpful for protecting against lung cancer. Amazingly, even for people who currently smoke or have smoked in the past, getting plenty of antioxidants from food still appears to help reduce lung cancer risk! This shows us how powerful diet can be for reducing cancer risk.

The nutrients that were part of the dietary antioxidant index included carotenes, flavonoids, vitamin E, selenium and vitamin C. Use the following information to help yourself eat more foods that give you plenty of these different antioxidants.

Good Food Sources of Carotenes (38)

Yellow-Orange Vegetables Green Leafy Vegetables Apricots Asparagus Beet Greens Bok Choy Broccoli Brussels Sprouts Cabbage Cantaloupe Carrots Cherries Chinese Broccoli Collard Greens Corn Cucumber, with peel

Dandelion Greens Endive Green Beans Grapefruit, especially pink Guava Kale Kohlrabi Lemons Mangos Mustard Greens Okra Orange Papayas Passion Fruit Peas, green Peppers, all colors

Persimmon Plantains Prunes Pumpkin Salmon (wild, caught) Spices (green, fresh) Spinach Squash Sweet Potatoes Swiss Chard Tangerine Tomatoes, especially cooked Turnip Greens Vegetable Juice Vegetable Soup Watermelon

Good Food Sources of Flavonoids (39)

Apples Blueberries Blackberries Black Currants Black Tea Brussels sprouts Buckwheat Capers, canned Celery Cherries Cherry Tomatoes Cranberries Dark chocolate Dill spice Fennel

Grapefruit Grapes Green Cabbage Green Tea Kale Kumquats Lemons Limes Mint Onions Oranges Parsley Pears Peppers, spicy Plums

Pomegranates Pummelo Radishes Raisins Raspberries Red Cabbage Red Currants Rhubarb Soybeans Spinach Strawberries Tangerines Tarragon Thyme

*Juice of the fruit also is a good source of flavonoids. Be sure to use only 100% juice. Avoid fruit cocktails and fruit drinks, which contain very little real fruit juice.

*Spices, such as dill, parsley, mint and thyme are loaded with flavonoids. Both fresh and dried spices contain these healthy nutrients.

Good Food Sources of Vitamin E (38)

Almonds Asparagus Beet Greens Broccoli Canned Tomato Products Carrot Juice Collard Greens Cooking Oils Dandelion Greens

Hazelnuts Fortified Cereals Mangoes Mustard Greens Papayas Peanuts Peppers, sweet Pinenuts Pistachio nuts

Pumpkin Raspberries Sardines Soy Milk Spinach Sunflower seeds Sweet Potatoes Turnip Greens Wheat Germ

*Nuts, fortified cereals, and cooking oils are the best sources of vitamin E.

Good Food Sources of Selenium (38)

Barley Brazil Nuts* Chicken Cous Cous Fish, all types

Mixed Nuts Mushrooms Oat Bran Part skim Ricotta cheese Rice, brown & white

Sunflower weeds Tuna fish Turkey Whole Wheat Flour

*Brazil nuts are the best food source of selenium. A single Brazil nut contains about 100 micrograms (mcg) of selenium, which is nearly double the Recommended Dietary Allowance (RDA) for selenium! Make it a habit to eat a couple of Brazil nuts each day and you will get more than enough selenium in your diet.

Good Food Sources of Vitamin C (38)

Apricot nectar Asparagus Beet Greens Broccoli Brussels sprouts Cabbage Cantaloupe Cauliflower Cranberry juice Grapefruit

Kale Kiwi Kohlrabi Kumquats Lemons Limes Mangos Oranges Papaya Peppers, hot green chili Pineapple

Peaches Peas, in pod Raspberries Strawberries Sweet green peppers Sweet potatoes Sweet red peppers Tangerines Tomato soup Turnip Greens Vegetable juice

*Juice of the fruit also is a good source of Vitamin C. Be sure to use only 100% juice. Avoid fruit cocktails and fruit drinks, which contain very little real fruit juice.

As you can see, there are many, many foods that you can eat to get more antioxidants into your diet.

NOTE: If you are in cancer treatment, these diet changes may not be right for you.

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Publish Date: 03/2005