Frequently Asked Questions about Diet, Physical Activity and Cancer
Because there is particular interest in the relationship between certain foods, nutrients and lifestyles and certain cancers, research on health behaviors and cancer risk is often publicized. Health professionals advising patients should make it clear that research is never-ending and that individual news reports may overemphasize conflicting or contradictory results. In brief news stories, reporters often fail to place new research findings in the proper context of the previous afternoon. There is very little, if any, advice on the best diet and physical activity to change diet and exercise levels based on a single study or news report. The questions and answers that follow address common concerns about the relationship between diet and physical activity and cancer.
Alcohol
Does alcohol consumption increase cancer risk? Yes. Alcohol consumption increases the risk of oral, pharyngeal, laryngeal, esophageal, liver, bowel, and breast cancers.2 331 People who drink alcohol should limit their alcohol consumption to no more than 2 drinks per day for men and no more than 1 drink per day for women.19 One drink is defined as 12 ounces of beer, 5 ounces of white wine, or 1.5 ounces of 80 proof spirits. The increased risk of cancer associated with drinking alcohol and smoking together is much greater than the effect of alcohol and smoking alone on cancer risk.2 Women who regularly drink several glasses of alcohol per week are associated with an increased risk of breast cancer.2 214 Women with a high risk of breast cancer may want to consider abstaining from alcohol.
Antioxidants
What are antioxidants and what can they do about cancer? The body uses certain nutrients, bioactive components of foods, and endogenously produced compounds to protect tissues from damage that would be caused by normal oxidative metabolism. Because such damage is associated with an increased risk of cancer, some antioxidants are thought to prevent cancer.332 Antioxidants include vitamin C, vitamin E, carotenoids, and some other phytonutrients. Studies have found that people who eat higher amounts of antioxidant-rich fruits and vegetables may reduce their risk of certain cancers.91 However, this does not mean that the benefits of fruits and vegetables come primarily from their antioxidant content, but rather from other phytonutrients. Some randomized controlled trials of antioxidant supplements did not find that these supplements reduced cancer risk; indeed, some of them who took antioxidant supplements had an increased cancer risk instead.125 333 (See “beta-carotene,” “lycopene “, “vitamin E” and “supplements”) The best advice available to reduce cancer risk is to consume antioxidants through food rather than supplements.
Beta-Carotene
Can beta-carotene reduce cancer risk? Beta-carotene, a type of antioxidant known as carotenoids, is found in dark orange-colored plants. Unlike other carotenoids, beta-carotene is a precursor to vitamin A. Vitamin A promotes cell differentiation and is thought to help prevent cancer. beta-carotene is found in fruits and vegetables, and since eating vegetables and fruits is associated with a lower risk of cancer, it seems plausible that consuming high doses of beta-carotene supplements may lower cancer risk. However, the results of some major clinical trials suggest otherwise. In two other studies, volunteers who took high doses of beta-carotene supplements to prevent lung and other cancers were found to have an increased risk of lung cancer in volunteers who smoked, and the results of a third study indicated that beta-carotene supplements were neither good nor bad for cancer prevention.129 334 Therefore, the intake of vegetables and fruits containing beta-carotene may be useful, but should be avoided. but high doses of beta-carotene supplements should be avoided, especially in people who smoke.
Calcium
Is calcium related to cancer? Some studies suggest that foods high in calcium may help reduce the risk of bowel cancer and that calcium supplements may slightly reduce the recurrence of bowel adenomas.239 However, there is also some evidence linking calcium, whether through calcium supplements or food, to an increased risk of prostate cancer.2 240 Given this situation, men should consume calcium through food, but not at levels above the recommended dose. Because women are not at risk for prostate cancer, but are at higher risk for osteoporosis, they should try to consume the recommended dose of calcium levels, primarily through food. The recommended level of calcium intake is 1,000 mg/day for people aged 19-50 years and 1,200 mg/day for people older than 50 years.335 Dairy products are a very good source of calcium, as are leafy and green vegetables. People who consume large amounts of calcium through dairy products should choose low-fat or fat-free products to reduce their saturated fat intake.
Coffee
Does coffee cause cancer? No. Speculation about the relationship between coffee and pancreatic cancer has been widely published in the past and remains unproven, including a study that found an inverse relationship.336 A clear inverse relationship between coffee and the risk of fatal prostate cancer was also recently found.337 Meanwhile, there is no evidence that coffee or caffeine increases cancer risk.
Dietary Supplements
Do dietary supplements reduce the risk of cancer? Current knowledge suggests that they do not reduce the risk of cancer. However, foods rich in vegetables, fruits, and other plant-based foods may reduce cancer risk, and there is little evidence that dietary supplements reduce cancer risk.125 One exception may be calcium, and calcium supplements may reduce the risk of bowel cancer (see “Calcium” above). In fact, evidence suggests that some high-dose nutrient supplements can increase cancer risk.335 338 339 For other reasons than cancer prevention, some dietary supplements may be beneficial for certain populations, such as pregnant women, women of childbearing age, and people on controlled diets. If dietary supplements are taken, the best advice is to take a balanced multivitamin/mineral supplement rather than a 100% “daily nutrient intake” of key nutrients.
Can I get the same value of vegetable and fruit nutrition from a pill? No. There are many healthy compounds found in vegetables and fruits that are likely to have a synergistic effect on health promotion. They may be important, but it has not been established that dietary supplements do not include ingredients found in whole foods. In addition to single or combination vitamin supplements, certain supplements have been described as containing the same nutritional value as vegetables and fruits. However, small doses of dry powder in pills usually contain only a small portion of whole foods. Food is the best source of vitamins and minerals.
Fats
Will eating less fat reduce cancer risk? The idea that consuming fat may cause cancer comes from a comparison of geographic locations, which found that people in countries with high-fat diets had a higher risk of breast, prostate, bowel and other cancers. Animal studies have found that high-fat diets cause more cancers. However, more rigorous investigations in humans have not found convincing evidence that high fat intake increases cancer risk or that lowering fat intake decreases cancer risk. One recent study found that for postmenopausal women, a low-fat diet had at best a slight effect on breast cancer risk.155 A large number of prospective studies have examined the effect of fat intake on the risk of breast, bowel, and prostate cancers, but currently, all evidence does not support a relationship between total fat intake and cancer risk.2 340 341
Fiber
What is dietary fiber and can it prevent cancer? Dietary fiber includes a large amount of many plant carbohydrates that are not digested by the body. Dried legumes, vegetables, whole grains and fruits are all good sources of dietary fiber. Fiber is classified by species as “water-soluble” (such as oat bran, pea, soy and psyllium fiber) or “non-water-soluble” (such as wheat bran, fruit peels, nuts, seeds and cellulose). Recent studies suggest that dietary fiber is associated with a reduced risk of various cancers, particularly bowel cancer, although it is unclear whether the effect is due to fiber or another component of high-fiber foods.15 169 177-179 These findings are one reason why the American Cancer Society guidelines recommend consuming high-fiber foods, such as whole grains, vegetables, and fruits for cancer prevention, but there are no clear recommendations for fiber supplements. recommendations.
Fish
Can eating fish prevent cancer? Fish is rich in natural omega-3 fatty acids. Animal studies have found that these fatty acids may prevent the development of cancer or hinder its progression, but the evidence for their benefits in humans is limited.2 342 The consumption of fish rich in omega-3 fatty acids has been associated with a reduced risk of cardiovascular disease, and some species of fish may contain high levels of mercury and polychlorinated biphenyls (PCBs), toxins and other environmental contaminants. Concentrations of these substances are highest in older, larger, predatory fish such as swordfish, tuna, squareheads, sharks, and king mackerel. In addition, some studies say that artificially fed fish may carry more of these harmful substances than wild fish. Pregnant women, women preparing to become pregnant, or women who are breastfeeding, and young children should eat less of these artificially farmed fish and should limit their intake of albacore tuna to no more than 6 ounces per week and canned tuna to no more than 12 ounces per week.343 Consumers should be advised to vary the types of fish they eat and reduce their intake of fish with high concentrations of harmful substances.
Folic acid
What is folic acid and can it prevent cancer? Folic acid is a B vitamin that is naturally found in large amounts of vegetables, legumes, fruits, whole grain cereals and fortified breakfast cereals. Since the 1990s, several prospective cohort studies have suggested that folic acid deficiency may increase the risk of bowel and breast cancers, especially in those who drink alcohol. However, in the United States since 1998, folic acid has been added to cereal concentrate products in the form of B vitamins. As a result, substantial folic acid deficiency is no longer a public health problem in the United States. Some studies have found that folic acid supplementation may increase the risk of prostate cancer and advanced colorectal adenoma344 345 as well as breast cancer346. Given these potential adverse effects of folic acid supplements, the likelihood of deficiency from food sources is low, and it is best to obtain folic acid by consuming vegetables, fruits, and whole-grain cereal products.
Garlic
Does garlic protect against cancer? The onion plant complex contains garlic and other vegetables of the onion family, and their claims of health benefits have been widely published. The ability of garlic to reduce cancer risk is currently being studied, and some studies have found that garlic may reduce the risk of bowel cancer.2 There is a similarly small amount of evidence that supplements of the Allium plant complex can also flip the switch. Garlic and other onion family foods, which may be included in a wide range of vegetables, have been recommended for cancer prevention.
Genetically Modified Foods
What are genetically modified foods and are they safe? Genetically modified, or bioengineered, foods increase a plant’s resistance to insects; delay spoilage; or improve portability, taste, nutrient content, or other desired values by adding genes from other living plant microorganisms. In recent years, a growing number of genetically engineered food products have emerged. In the United States, for example, greater than 90% of soybeans and 70% of corn are grown from herbicide-resistant genetically engineered seeds, such as corn, that produce insecticides, and in natural cases Bacillus thuringiensis that produce insecticides.347 As presented, the use of genetically engineered seeds has generated concern about their safety and potential effects on human health.348 Theoretically, these added genes could produce substances that are allergenic or have individual allergic side effects, or may lead to the appearance of elevated levels of substances that are harmful to the body.349 Conversely, public health concerns may also promote GM crops. For example, genetic modification to increase the amount of folate in various types of plants has generated a great deal of interest.350 At the same time, there is no evidence that GM foods currently on the market or substances found in GM foods are substances that are harmful to health or that increase or decrease the risk of cancer because of the addition of genes.349
However, the absence of evidence of harmful effects is not the same as this evidence that all GM foods are safe, because the promotion of these food supplies is relatively near-term and the long-term health effects are unclear. Ongoing assessments of the safety of genetically modified foods are important to ensure their safety, and to reinforce confidence that their use is valuable.351 Examples of genetically modified foods approved for sale in the United States include carrot, corn, tomato, and soy varieties. The U.S. Environmental Protection Agency (EPA), the U.S. Food and Drug Administration (FDA) and the U.S. Department of Agriculture work together to oversee these foods.
Irradiated Foods
Can irradiated foods cause cancer? There is no evidence that irradiated foods can cause cancer or are harmful to health. Irradiation is increasingly being used to kill harmful organisms in foods and to extend their shelf life. The rays do not linger on the food after irradiation is over, but there is also no evidence that the intake of irradiated food increases the risk of cancer 352 353.
Meat: cooking and storage
Should I avoid eating meat? Numerous epidemiological studies have confirmed the association between the intake of large amounts of processed meat and an increased risk of bowel and stomach cancer.2 15 135 This association may be due in part to nitrites, which are added to many lunch meats, burgers, and hot dogs in order to maintain color and prevent contamination with pathogenic bacteria. Ingested processed meats and meat preservation methods involving smoking or salt increase exposure to potentially cancer-causing chemicals and should therefore be minimized.
How does cooking meat affect cancer risk? Proper cooking is necessary to kill harmful microorganisms in meat and can prevent disease. However, some studies say that frying, grilling, or barbecuing meat at high temperatures can produce a number of chemicals (polycyclic aromatic hydrocarbons or heterocyclic aromatic amines) that may increase cancer risk.144 Although studies say that these chemicals can damage DNA in animals and cause cancer, it remains unclear how much of them, rather than the other compounds in meat, is needed to increase bowel cancer risk. A growing body of literature examining exposure to these compounds and the assessment of cancer risk2 currently appears to provide at least a partial explanation for the positive relationship between meat intake and bowel or other cancers. Techniques such as braising, steaming, low-temperature cooking, steaming, and microwaving meats can minimize the production of these chemicals.
Non-nutritive sweeteners and sugar substitutes
Do non-nutritive sweeteners or sugar substitutes cause cancer? There is no evidence that sweeteners, within the intake levels of the human diet, can cause cancer. Aspartame, saccharin and sucralose are a few of the non-nutritive, synthetic sweeteners approved by the FDA for use in the United States. Current evidence does not suggest a relationship between intake of these compounds and increased cancer risk.354-356 Some animal studies have found that their use may be associated with an increased risk of bladder cancer, brain cancer, or hematopoietic tumors, but no increased cancer risk has been found in human studies.357 358 People with inherited phenylketonuria should avoid aspartame in their diet. The latest sugar substitutes include sweeteners such as sugar alcohols (e.g., sorbitol, xylitol, and mannitol) and natural sweeteners (e.g., syrups of stevia and agave). All sweeteners appear to be safe when properly ingested, although large amounts of xylitol may cause abdominal bloating or abdominal discomfort in some people.
Obesity
Does being overweight increase the risk of cancer? Yes. Overweight and obesity are clearly associated with an increased risk of cancer, including breast cancer in postmenopausal women,14 colon and rectal cancer,15 endometrial cancer, esophageal adenocarcinoma, kidney cancer, and pancreatic cancer.2 Obesity may increase the risk of bladder cancer.2 Being overweight and obese may be associated with an increased risk of liver cancer, non-Hodgkin’s lymphoma, multiple myeloma, cervical and ovarian cancer, and malignant prostate cancer.
Although there is limited research on whether weight loss reduces cancer risk, some studies have found that reducing weight does reduce the risk of postmenopausal breast and other cancers.76-79 359 360 Because weight loss has been shown to have health benefits, people who are overweight are encouraged to stop gaining weight and then start losing it and preventing rebound. Avoiding excess weight gain in adulthood is important not only for reducing the risk of cancer, but also other chronic diseases.17 18
Olive oil
Does olive oil affect cancer risk? The intake of olive oil is associated with a reduced risk of cardiovascular disease and not with an increased risk of cancer, most likely being neutral in cancer risk. Olive oil, although rich in monounsaturated fats, is a healthy alternative to butter and margarine, is a significant source of high calories and contributes to excessive energy intake.
Organic foods
Are foods labeled as “organic” more effective in reducing cancer risk? The term “organic” is often used to refer to plant-based foods that are grown without artificial chemicals. Organic animal foods are those that are raised without the intake of hormones or antibiotics. Organic plant foods are those grown without the use of conventional pesticides or herbicides, chemical fertilizers or sewage sludge as fertilizer or irradiated during food processing. Genetically modified foods are not organic. While organic food is produced with the purpose of promoting sustainable agricultural practices, it is widely believed that ingesting organic food may provide health benefits. There is some debate as to whether organic produce may have higher levels of nutrition than conventionally grown plants. But currently, there are no studies that can prove whether organic foods can juvenilely reduce cancer risk or provide other health benefits over products produced by other farming methods.
Pesticides and herbicides
Do pesticides in food cause cancer? Pesticides and herbicides are toxic when used inappropriately in industry, agriculture or other occupations. Although vegetables and fruits contain low levels of residual chemicals, a large body of scientific evidence supports the health benefits and cancer prevention benefits of vegetable and fruit intake.2 Currently, there is no evidence that low doses of residual pesticides and herbicides in food increase cancer risk. However, they should be washed thoroughly before ingestion to reduce not only exposure to these compounds, but also the health risks of disease from microbial contamination.
Physical Activity
Will increased physical activity reduce cancer risk? Yes. People who engage in moderate to vigorous physical activity have a reduced risk of certain cancers, including breast cancer, bowel cancer, endometrial cancer and advanced prostate cancer.2 69 94 95 For some cancers, the reduction in risk is not related to the effect of exercise on body weight. Data on the direct effect on the risk of developing other cancers are more limited. Nevertheless, physical activity is a key component in maintaining or achieving a healthy weight, and overweight and obesity are associated with other types of cancer.2 In addition, physical activity is beneficial for cardiovascular disease, diabetes, and other diseases.20 361
Phytonutrients
What are phytonutrients and can they reduce the risk of cancer? The term “phytonutrients” relates to a variety of compounds that occur naturally in different plants. Some of these compounds protect plants against insects or protect other important biological functions. Some are either antioxidants or act as hormone analogues in the plant body and in the human body when they are ingested. Because the intake of vegetables and fruits is associated with a reduced risk of cancer, researchers have tested a large number of phytonutrients in studies of specific components that may explain their beneficial effects. But there is no evidence that, like vegetables, fruits, legumes, and grains, the phytonutrients from which they are derived are beneficial as supplements for long-term physical health. Examples of phytonutrients include flavonoids (found in soybeans, chickpeas, and tea), carotenoids (found in pecan trees, cantaloupe, and carrots), anthocyanins (found in eggplant, red kale), and sulfides (found in garlic and onions).
Salt
Does a diet high in salt increase cancer risk? There is solid evidence that consumption of large amounts of foods preserved by salt, i.e., salt-cured products, and pickled foods increases the risk of stomach, nasopharyngeal, and throat cancers.2 In general, these foods are not a major part of most people’s diets in the United States. However, minimizing the consumption of salted or pickled foods may help prevent some cancers. There is no evidence that salt added to cooking or seasoning foods can affect cancer risk. In the United States, although practical salt does not pose much risk of cancer, it can increase the risk of hypertension and cardiovascular disease, so the 2010 U.S. Dietary Guidelines19 and the American Heart Association17 suggest reducing salt intake.
Selenium
What is selenium and can it reduce the risk of cancer? Selenium is a mineral that contributes to the defense mechanism of antioxidants. Animal studies suggest that selenium may prevent cancer, and one experimental trial found that selenium supplements may reduce the risk of lung, bowel, and prostate cancers.362 However, selenium supplements were found to have no effect on prostate cancer incidence in a hypothetical randomized trial.120 Therefore, there is no reliable evidence that selenium supplements reduce cancer risk.363 Therefore, selenium supplements are not recommended and should avoid taking high doses of selenium supplements because there is only a thin line between safe and toxic doses. The maximum daily dose should be no more than 20 μg.
Soy-based products
Can soy-based foods reduce cancer risk? Like other legumes or legumes, soy and foods derived from soy are rich in high-quality protein and are therefore a good substitute for meat. Soy contains a number of phytonutrients and is also a good source of isoflavone phytonutrients, which can reduce estrogenic activity and may prevent hormone-dependent cancers.
There is increasing evidence from epidemiological studies that consumption of traditional soy-based products such as tofu may reduce the risk of breast, prostate, and endometrial cancers, and there is also some selected evidence of a reduction in some other cancers.2 Whether these observations apply to products containing soy isolate or to tissue proteins derived from soy is unclear. The basis for supporting the consumption of supplements containing soy isolate phytonutrients to reduce cancer risk is limited or data are lacking.
Sugar
Can sugar increase the risk of cancer? Sugar contributes to calorie intake and does not contain any nutrients that can reduce cancer risk. By promoting obesity, high sugar intake may indirectly increase cancer risk. White sugar (refined sugar) and brown sugar (unrefined sugar) or honey have the same effect on body weight and insulin. Limiting foods such as cakes, candy, cookies, sweetened cereals and sweetened beverages such as soda and sports drinks can help reduce calorie intake.
Tea
Can drinking tea (green or black) reduce cancer risk? Tea is a beverage that comes from a concoction of leaves, bud germ or within the branches of a tea tree. Black tea, green tea, white tea, pu-erh tea, and different varieties of tea all come from the same plant, but respond to their different processes. Some researchers have suggested that tea may protect against cancer due to its content of antioxidants, polyphenols, and flavonoids. In animal studies, some teas (including green tea) have been shown to reduce cancer risk.364 465 However, epidemiological studies have found mixed results.2 Currently, although laboratory findings have been promising, and drinking tea is part of many cuisines, the evidence does not support the core reason for drinking tea as a cancer preventative.
Trans Fats
Do trans fats increase cancer risk? Trans fats are created during the processing of hydrogenated vegetable oils, such as margarine or shortening, which can then be allowed to become solid at room temperature. Trans fats have adverse cardiovascular effects, such as increased LDL levels and increased risk of heart disease.17 194 Their relationship with cancer risk has not been established. In any case, it is recommended to reduce or avoid trans fats due to the risk it poses for cardiovascular disease. This is part of the recommendations of the 2010 American Dietary Guidelines19 and the American Heart Association17.
Ginger and other spices
Can ginger and other spices reduce the risk of cancer? Research on the effects of ginger on cancer prevention is ongoing.366 Other spices, including cayenne pepper (paprika), cumin, and curry, are also being studied for their effects on cancer prevention.367 368 However, some studies on the long-term effects of these spices on human diseases, such as cancer, are lacking.
Vegetables and fruits
Does eating vegetables and fruits reduce the risk of cancer? Yes. Although the strong evidence that consuming vegetables and fruits reduces cancer risk has been weakened by the recent publication of more null studies or studies with only weak effects, the overall evidence suggests that consuming vegetables and fruits reduces the risk of some cancers, including lung, oral cavity, pharynx, larynx, esophagus, stomach, and intestinal cancers.2 Different types of vegetables and fruits may reduce certain cancers to varying degrees of Risk. It is not known which compounds in vegetables and fruits are most likely to protect against cancer, and different vegetables and fruits may be rich in different types of phytonutrients that may protect against cancer. Recent studies have found that increased intake of vegetables and fruits may help reduce the risk of obesity149-151 and, therefore, may well provide indirect protection against cancer. The best recommendation is to use at least 2.5 cups of a variety of colorful vegetables and fruits each day.
Is there a difference in the nutritional value of fresh, frozen and canned vegetables and fruits? Yes, there is, but they are all good choices. Fresh foods are products that are consumed immediately after receipt and are usually considered to have the most nutritional value, and their taste is often not comparable to the same frozen or canned products. However, often frozen foods can be more nutritious than fresh foods because they are multi-selected and frozen quickly; nutrients can be lost between the time the food is received and the time it is consumed. Canned foods are more likely to have reduced temperature sensitivity and water-soluble nutrients because high temperatures are a necessary part of the manufacturing process for canned foods. Be aware that some fruits packaged in highly concentrated syrups and some canned vegetables contain high concentrations of salt. Choose different forms of vegetables and fruits.
Does cooking affect the nutrients in vegetables? Boiling vegetables, especially for long periods of time, can leach out their water-soluble vitamins. Because some potentially beneficial phytonutrients are fat-soluble, frying them in oil may increase the utilization of these compounds, and cooking in general can also break down cell walls, thus allowing nutrients and other phytonutrients to be more easily digested and absorbed. Microwaving and steaming are the best ways to preserve the nutrient content in vegetables. Eating vegetables raw, such as Sarah, also preserves the nutritional content of the food. As with other suggestions for consuming a variety of vegetables, consuming foods made by different cooking methods may improve the utilization of various nutrients and phytonutrients.
Should I juice my vegetables and fruits? Juicing can add variety to your diet and is a great way to consume fruits and vegetables, especially for those who have difficulty chewing and swallowing. Juicing can improve the absorption of nutrients from vegetables and fruits. However, juices contain less fiber and may contain less fiber than in whole vegetables and fruits. Consuming large amounts of juice provides quite a bit of energy to a person’s diet. Commercial juice products should be 100% fruit or vegetables and should be pasteurized to destroy harmful microorganisms.
Vegetarian Diet
Can a vegetarian diet reduce the risk of cancer? A vegetarian diet includes many health-promoting features: it tends to be low in saturated fatty acids, high in fiber, vitamins and phytonutrients369 and does not contain the intake of red and processed meats. Therefore, it is reasonable that a vegetarian diet may reduce cancer risk.370 Recent studies in the UK comparing vegetarians and non-vegetarians found that vegetarians at some cancer sites had a lower overall cancer risk.371 372 Whether a vegetarian diet may provide particular benefits through the diet is not clear, including a lower intake of animal foods than the typical Western diet ; indeed, in a British study of vegetarians, people who ate fish and no other meat had a lower cancer risk than vegetarians.371 A strict vegetarian diet involves avoiding all products of animal origin, including milk and eggs, and mentions that an absolute vegetarian diet can benefit by taking vitamin B12, zinc, and iron supplements, especially for children and menopausal women.91 They should have adequate calcium intake, as absolute vegetarians with relatively low calcium have a higher risk of fracture compared with vegetarians or people consuming a diet containing meat.373
Vitamin A
Can vitamin A reduce the risk of cancer? Vitamin A (retinol) can be obtained from food in two ways: from animal sources and from beta-carotene and other vitamin A precursors found in plant foods. Vitamin A maintains healthy tissues. Vitamin A supplements have not been found to reduce cancer risk, and high doses of vitamin A can, in fact, increase the risk of lung cancer in smokers and those who have quit smoking.
Vitamin C
Can vitamin C reduce cancer risk? Vitamin C is found in many fruits and vegetables, especially oranges, grapes and peppers. Many studies have found that consuming foods rich in vitamin C is associated with a lower risk of cancer.2 However, in some studies where vitamin C was used as a supplement, it was not found to reduce cancer risk.
Vitamin D
Can vitamin D reduce cancer risk? There is growing evidence from epidemiological studies that vitamin D may help prevent bowel cancer,19 235 but current evidence does not support its association with other cancers.335 374 Randomized controlled trials are currently underway, but results are not available in recent years. The Institute of Medicine recently increased its recommendation for daily intake of vitamin D based on the level needed for bone health, which requires 400 to 600 international units (IU) per day for most adults and 800 IU per day for those at or above age 70. The maximum daily intake considered safe has been increased from 2,000 IU to 4,000 IU.
Vitamin D is produced through skin exposure to ultraviolet light; through diet, especially products with added vitamin D, such as milk and cereals; and through supplements. Many Americans, however, do not consume adequate amounts of vitamin D and are at risk for deficiency, especially those with dark skin, those who are not exposed to sunlight, the elderly, and exclusively breastfed infants.375
Vitamin E
Can vitamin E reduce cancer risk? Alpha-tocopherol is considered the most active form of vitamin E in the body and is a very powerful biological antioxidant. In the Alpha-Tocopherol and Beta-Carotene Cancer Prevention Study (ATBC), a reduced incidence of prostate cancer was observed in men randomly assigned to receive alpha-tocopherol, where this trial included only male smokers.129 This finding helped inspire the design of the SELECT trial, which specifically investigated the role of selenium and vitamin E supplements in prostate cancer prevention. However, the results confirmed that these supplements did not reduce the likelihood of prostate cancer.120 Indeed, if anything, the cancer risk may be elevated in those men taking vitamin E supplements. The Heart Prognosis Prevention Evaluation (HOPE) trial was designed to examine overall cancer incidence, mortality, and cardiovascular disease, comparing vitamin E supplements with a blank group.376 There was no difference between the vitamin E supplements and the blank group in terms of cancer rates or heart disease rates. The rate of heart failure was indeed higher in the group taking vitamin E supplements.376 Although foods containing vitamin E, including nuts and some unsaturated fatty acid oils, are healthy and have been shown to reduce the risk of heart disease, vitamin E supplements are not recommended for the prevention of cancer or chronic disease.