What you may have heard

Smoking e-cigarettes or vaping can increase your risk of lung cancer.

What science tells us

These products are known by many names including e-cigs, vape pens, vaporizers, and electronic nicotine delivery systems (ENDS). They consist of a battery that turns the device on, a cartridge containing liquid (or “pod”), and a heating element that heats the contents of the pod. E-cigarettes are still fairly new and more research is needed over a longer time to determine what the long-term effects on cancer may be (ACS). E-cigarettes have become very popular and their possible link to cancer have often made headlines. While e-cigarettes do not contain tobacco, most contain nicotine, which can come from tobacco; as a result, the FDA characterizes them as tobacco products.

The FDA does not require testing of all substances in e-cigarettes to ensure that they are safe. In addition, most products do not list all of the harmful or potentially harmful substances contained in them. The US Centers for Disease Control and Prevention (CDC) has stated that e-cigarette products may contain harmful or illegal substances from unknown origins.

Epidemiological Evidence

Scientists are unsure whether or not e-cigarettes cause cancer, although they are known to contain cancer-causing chemicals. The aerosol “vapor” of an e-cigarette is not water vapor but contains a range of substances that may include:

• volatile organic compounds (VOCs), which can cause eye, nose, and throat irritation; headaches; nausea; and damage to the liver, kidney, and nervous system;
• glycerin, which is linked to loss of lung function when inhaled; and
• flavoring chemicals, such as diacetyl, which has been linked to bronchiolitis obliterans, a serious lung disease.

Formaldehyde, a known carcinogen, is produced if the e-liquid overheats or not enough liquid is reaching the heating element (ACS).

Toxicology Evidence

E-cigarette vapor is linked to lung cancer in many animal studies (NIH). Several animal studies have concluded that daily exposure to e-cigarettes increased cell tumor growth (Marczylo). 

IARC Carcinogen Classification:

Not classified (although some components of e-cigarette vapor are carcinogens, including formaldehyde, a Group 1 carcinogen, known to be carcinogenic to humans)

How to reduce your risk

E-cigarette use exposes people to potentially serious health risks. It’s important to stop using all tobacco products, including e-cigarettes, as soon as possible to avoid becoming (or staying) addicted to nicotine (JHU). If you are having trouble quitting e-cigarettes on your own, get help from your doctor or from other support services such as your state’s Quitline (1-800-QUIT-NOW) or the American Cancer Society (1-800-ACS-2345).

Bottom line

There is not enough evidence yet to say that e-cigarettes cause cancer. However, e-cigarettes do not consist of water vapor alone, but contain a range of substances, including cancer-causing chemicals. E-cigarettes should be avoided because their use may lead to nicotine addiction and many other serious health conditions.

What you may have heard

Tobacco use is a leading cause of cancer and cancer death. It is also the biggest preventable cause of cancer.

What science tells us

All tobacco products, including cigarettes, cigars, pipe tobacco, chewing tobacco, and snuff contain poisonous substances, cancer-causing agents, and nicotine (a highly addictive substance).

Cigarettes are the most common form of tobacco used and are responsible for about 90% of all lung cancers, according to the American Lung Association (Johns Hopkins).

Epidemiological Evidence

Both people who smoke and people who inhale secondhand smoke have an increased risk of cancer, because tobacco has chemicals that cause DNA damage. Tobacco use causes many types of cancer:  lung, larynx (voice box), esophagus, throat, bladder, kidney, liver, stomach, pancreas, colon, rectum, and acute myeloid leukemia (cancer of the blood and bone marrow) (NCI).

Cigars and pipes are often branded as a less harmful way to smoke tobacco; however, cigar and pipe smokers are at increased risk for cancer of the oral cavity, esophagus, voice box, and lungs. Pipe smokers are also at increased risk for lip cancers because of where the pipestem rests (Johns Hopkins).

People who use smokeless tobacco (snuff or chewing tobacco, which is placed between the cheek and the gum) have an increased risk of cancers of the mouth, esophagus, and pancreas (Johns Hopkins). Over 28 cancer-causing chemicals have been found in smokeless tobacco.

Laboratory Evidence/ Supportive Evidence

Animal models have also confirmed that tobacco smoking not only increases the risk of lung cancer, but lifetime exposure to tobacco smoke also increases the risk for lung cancer (Hecht). 

IARC Carcinogen Classification:

Group 1 (carcinogenic to humans)

How to reduce your risk

There is no safe level of tobacco use. People who use any type of tobacco product are strongly urged to quit. Scientific evidence shows that people who quit smoking, regardless of their age, have large gains in life expectancy compared to people who continue to smoke (NCI). Also, quitting smoking when diagnosed with cancer reduces the risk of cancer death.

If you are having trouble quitting on your own, get help from your doctor or from other support services, such as your state Quitline (1-800-QUIT-NOW) or the American Cancer Society (1-800-ACS-2345). The American Cancer Society recommends picking a stress-free time to quit, asking for support and encouragement from family and friends, doing some exercise or activity each day to relieve stress, joining a stop-smoking program, and talking with your healthcare provider about medicines that may help you quit (Johns Hopkins).

Bottom line

Tobacco use does increase risk of cancer. Avoid smoking and smoke exposure. Resources are available to help you quit smoking.

Watch these videos about tobacco and cancer risk and lung cancer from the Dana-Farber Cancer Institute, and follow the links below for more information.

What you may have heard

A disrupted sleep cycle reduces our body’s ability to function properly and decreases its ability to ward off cancer (Shafi et al.).

What science tells us

The World Health Organization (WHO) states that circadian disruption alone is a risk factor for cancer.
“Circadian disruption” is defined as any change in sleep pattern, whether it is loss of sleep, difficulty falling asleep, or waking up during the sleep cycle. The body’s central clock is found in the brain and gets its cues largely from light. Presence of light tells our bodies that it is time to be awake, alert, and hungry. The body sets its clock on a 24-hour cycle (based on how much light it senses) and each organ system follows. Our circadian rhythm controls when we wake up, our appetite, our body temperature, and our mood. 

Epidemiological Evidence

People who experience jet lag, travel across multiple time zones, do shift work, have sleep disruption, or are exposed to light at night may be at an increased risk of cancers of the prostate, breast, colon, liver, pancreas, ovary, and lung (Shafi et al.). The International Agency for Research on Cancer (IARC), which categorizes cancer risk factors on a scale from cancer-causing (carcinogenic) to not carcinogenic to humans, states that night shift work alone is likely carcinogenic to humans (IARC).

Laboratory Evidence/ Supportive Evidence

Some animal models have been used in laboratory experiments to examine the relationship between lack of sleep and cancer rates. The results also support the conclusions found in human studies: that lack of sleep has complex effects on cancer biology(Yaacoby-Bianu & Hakim). 

IARC Carcinogen Classification:

Not classified.

How to reduce your risk

Sleep disruption and other cancer risk factors often appear together, such as workplace or social/life stressors, smoking, high alcohol consumption, poor diet, low physical activity, and obesity. Reducing these stressors and behaviors may decrease your chances of developing cancer.

The Centers for Disease Control (CDC) recommends regular health checkups and telling your doctor if you have any of the following symptoms: severe fatigue or sleepiness when you need to be awake, trouble with sleep or stomach, irritability, poor work performance (frequent mistakes, injuries, etc.), or unexplained weight gain or loss (CDC). In addition, try healthy behaviors to fight the effects of circadian rhythm disruption: get enough sleep, eat a nutritious diet, exercise regularly, avoid tobacco, and limit alcohol drinking (CDC).

The National Institute for Occupational Safety and Health (NIOSH) has a wide range of occupation-specific resources to help employers and workers better cope with the demands of shift work and long hours (NIOSH).

Bottom line

Circadian disruption is high among people who experience jet lag, travel across multiple time zones, work on overnight shifts, or are exposed to light at night. This population may have an increased risk of cancers of the prostate, breast, colon, liver, pancreas, ovary, and lung (Shafi et al.). It is important to talk with a health provider if you have sleep disruption and to seek resources to improve your quality of sleep.

What you may have heard

The Daily Mirror published a story in 2003 claiming that sitting too close to the TV for prolonged periods of time increases cancer risk.

What science tells us

Older TVs gave off low levels of radiation, but modern TVs are built with proper shielding, so people are protected from potential radiation exposures. The television itself does not increase cancer risk but is instead a symbol for a sedentary lifestyle.

Sedentary behavior is spending long periods of time sitting or lying down, whether this is watching TV, reading a book, sitting on a bus, or using a computer. This behavior is separate from the amount of time spent being physically active and the calories burned during exercise, although both a sedentary lifestyle and low levels of physical activity can contribute to other diseases.

Epidemiological Evidence

While certain types of radiation can cause cancer, there is no epidemiological evidence that you will have significant radiation exposure when sitting close to a TV. In contrast, the body burns very little energy while we are sitting and reduced calorie burning is linked to an increased risk of obesity (and higher levels of body fat), heart disease, and cancer (Cancer Research UK). Several published epidemiological studies have concluded that sedentary behavior increases the risk of developing cancer. 

Laboratory Evidence/ Supportive Evidence

Laboratory models using animals studied the relationship between exercise and tumor formation. Some studies have shown that exercise can greatly reduce the size of tumors in mice. 

IARC Carcinogen Classification:

Not classified.

How to reduce your risk

Becoming both more physically active and less sedentary helps you live a healthier lifestyle and reduces your risk of developing obesity, heart disease, and cancer (Cancer Research UK). Do at least 150-300 minutes of moderate physical activity weekly (this can be walking, running, swimming, doing chores, or even going shopping). Eating a healthy and balanced diet will also help reduce risk of weight gain.

Bottom line

Watching TV and distance to the TV do not cause cancer. However, a sedentary lifestyle (for example, a lot of TV watching) is associated with low levels of physical activity and contributes to increased risk of obesity, heart disease, and cancer.

What you may have heard

Obesity has been linked to various types of cancers.

What science tells us

Obesity or high body mass index (BMI) is a condition in which a person has an unhealthy amount and/or distribution of body fat. To measure obesity, researchers often use the BMI scale, which is determined by dividing a person’s weight (in kilograms) by their height (in meters) squared. BMI provides a more accurate measure of obesity than weight alone, though it has its limitations. Nearly 70% of U.S. adults have a BMI of 25.0 or higher, which is characterized as overweight (25.0-29.9) or obese (30.0 and above) (NCI).  However, there are many metrics of obesity, and each of these may be associated with different cancer risks.

Epidemiological Evidence

There is consistent evidence that higher body fat is linked to a number of cancers. People with obesity have chronic inflammation, which, over time, can cause DNA damage that leads to cancer. These people are also more likely to have conditions or disorders that are linked to or cause chronic inflammation: for example, Barrett’s esophagus, gallstones, ulcerative colitis, and hepatitis (NCI). Cancers linked to obesity include:

• Endometrial: Obese and overweight women are 2-4 times as likely as women with a healthy BMI to develop endometrial cancer (cancer of the lining of the uterus). Risk of endometrial cancer increases with increasing weight gain in adulthood (NCI).
• Esophageal: People who are overweight or obese are 2 times as likely as those with a healthy BMI to develop esophageal adenocarcinoma (NCI).
• Gastric cardia: People who are obese are nearly twice as likely as those of healthy weight to develop cancer in the upper part of the stomach, closest to the esophagus (NCI).
• Liver: People who are overweight or obese are up to twice as likely as those of healthy weight to develop liver cancer; this association is stronger in men (NCI).
• Kidney: People who are overweight or obese are up to twice as likely as those of healthy weight to develop renal cell cancer, the most common form of kidney cancer (NCI).
• Multiple myeloma: Multiple myeloma is a cancer that forms in a specific type of white blood cell (plasma cell) and accumulates in the bone marrow. Compared to healthy-weight individuals, overweight and obese individuals have a 10-20% increase in risk of developing multiple myeloma (NCI).
• Meningioma: A meningioma is a slow-growing tumor that develops in the membranes surrounding the brain and spinal cord. The risk of meningioma is increased by 50% in those who are obese and 20% in those who are overweight.
• Pancreatic: People who are overweight or obese are about 1.5 times as likely to develop pancreatic cancer (NCI).
• Colorectal: People who are obese are 30% more likely to develop colorectal cancer than healthy-weight individuals (NCI).
• Gallbladder: People who are obese have a 60% increase in risk of gallbladder cancer (NCI).
• Breast: Women in menopause who are obese have a 20-40% increase in risk of developing breast cancer (NCI).
• Ovarian: Higher BMI is associated with a 10% increase in risk of ovarian cancer among women who have never used menopausal hormone therapy (NCI).
• Thyroid: Higher BMI is associated with a 10% increase in risk of thyroid cancer among women who have never used menopausal hormone therapy (NCI).

In people who are diagnosed with breast, prostate, or colorectal cancer, research shows that obesity may worsen aspects of cancer survivorship (example: quality of life, cancer recurrence, cancer progression, and survival).

Laboratory Evidence/Supporting Evidence

The laboratory and animal study evidence generally supports the epidemiological evidence that obesity is associated with risk of a variety of cancers.

IARC Carcinogen Classification:

Not classified.

How to reduce your risk

Epidemiological studies provide consistent evidence that people who have a healthy BMI have lower risk of colon, kidney, breast, endometrial, and ovarian cancers (NCI). Studies have shown that people who lose weight have decreased risk of breast, endometrial, colon, and prostate cancers. People with obesity who have bariatric surgery appear to have lower risks of obesity-related cancers than those who do not have bariatric surgeries.

The steps to prevent unhealthy weight gain are the same as the steps to lose weight: exercising regularly, maintaining a healthy diet, and monitoring your weight. To prevent weight gain, 150-300 minutes of moderate-intensity activity per week is recommended (Mayo Clinic). A healthy diet includes low-calorie and nutrient-dense foods (such as fruits, vegetables, and whole grains), avoids saturated fat, and limits sweets, alcohol, and processed foods. Identifying situations that trigger overeating and monitoring these situations can also prevent weight gain. Finally, consistency in diet and exercise, and monitoring your weight regularly can help keep off excess pounds.

Bottom line

Obesity increases risk of endometrial, esophageal, gastric cardia, liver, kidney, multiple myeloma, meningioma, pancreatic, colorectal, gallbladder, breast, ovarian, and thyroid cancers. The steps to prevent unhealthy weight gain are the same as the steps to lose weight: Exercise regularly, maintain a healthy diet, and monitor your weight.

Learn More From These Trusted Sources

What you may have heard

Consuming burnt foods or burnt marshmallows increases the risk of developing cancer.

What science tells us

Marshmallows are composed of a majority of sugars. They are eaten alone, but sometimes are roasted over a fire to make s’mores. Many chemicals are found in burnt food including acrylamide, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic amines (HCAs) (Dana-Farber). Acrylamide forms naturally from chemical reactions in certain types of starchy foods when they are cooked at a high temperature. However, the chemical is only formed when food is cooked until it turns dark brown and if it is cooked over long periods of time (Dana-Farber). PAHs are released when fat and juices drip onto the flame while cooking meat. HCAs form when meat is exposed to high temperatures for a prolonged period of time (FDA). Neither of these are of concern with burnt marshmallows.

Epidemiological Evidence

According to the World Cancer Research Fund, there is no strong human evidence of a link between overcooked starchy foods and cancer risk (WCRF).

Laboratory Evidence/Supporting Evidence

There is no laboratory evidence that consuming burnt foods causes cancer.

IARC Carcinogen Classification:

Not classified (although some compounds that may be found in burnt marshmallows may contain chemicals that IARC has designated as carcinogenic).

How to reduce your risk

It is not clear if there is a relationship between overcooked starchy foods and cancer. To minimize acrylamide exposure when cooking other types of foods, minimize frying and deep frying, avoid storing potatoes in the refrigerator, and soak raw potato slices in water (and dab dry) before frying or cooking. To reduce HCA and PAH consumption when cooking meat, avoid direct exposure of meat to an open flame, keep the duration of cooking times as brief as you can, microwave meat prior to cooking it on a high temperature, remove charred portions when eating, use acidic-based marinades, or enjoy grilled vegetables and tofu as a meat alternative (Dana-Farber).

Bottom line

Though no specific studies have been done on the link between burnt marshmallows and cancer, eating burnt marshmallows is not likely to increase cancer risk.

What you may have heard

Given that cancer cells grow well in an acidic environment, many people have questioned whether a diet high in acidic foods can increase your risk of cancer.

What the science tells us

In chemistry, the pH scale is a measure for how acidic or basic a solution is. The pH scale ranges from 0-14: 7 is neutral, less than 7 is acidic and greater than 7 is basic.

Epidemiological Evidence

There are no human epidemiological studies that have studied the relationship between pH and cancer. 

Laboratory Evidence/Supporting Evidence

There is no laboratory evidence that acidic pH increases risk for cancer. While it is true that cancer cells grow well in an acidic environment, your body’s pH levels are not determined by the food you eat (MD Anderson). Factors that determine your body’s pH include fluid loss, electrolyte levels, and organ function.

Not Classified.

How to reduce your risk

Research shows that there is not one diet or one food that can prevent cancer. However, a balanced diet and getting enough physical activity can prevent excess weight gain, which is associated with cancer risk. To prevent weight gain, 150-300 minutes of moderate-intensity activity per week is recommended  (Mayo Clinic). A healthy diet includes low-calorie and nutrient-dense foods (such as fruits, vegetables, and whole grains), avoids saturated fat, and limits sweets and alcohol. Identifying situations that trigger overeating and having tools to address these situations can also help in preventing weight gain. Finally, consistency in diet and exercise and monitoring your weight regularly can help keep off excess pounds.

Bottom line

Your blood pH is not affected by your diet, and there is no one diet to prevent cancer. Instead, focus on eating a balanced diet and exercising regularly.

What you may have heard

Curcumin has been touted as having antioxidant, antiviral, antibacterial, and anti-inflammatory properties. One of curcumin’s newer areas being studied are its possible anti-cancer properties.

What science tells us

Curcumin (the part of turmeric that gives it its vibrant color) has gained attention in the media as a potential anti-cancer therapy.

Epidemiological Evidence

Studies of curcumin in humans are still in the early stages so more research is needed before we can say anything about a relationship between curcumin and cancer.

Laboratory Evidence/Supporting Evidence

Curcumin specifically targets cell signaling pathways that are involved in cancer development and growth, which could decrease cancer risk (Giordano et al.). Studies done in laboratory animals suggest that curcumin may prevent cancer, slow the spread of cancer, make chemotherapy more effective, and protect healthy cells from damage by radiation therapy.

IARC Carcinogen Classification:

Not classified.

How to reduce your risk

It is not known whether consuming products that contain curcumin, such as turmeric, decrease your chance of getting cancer.  Eating a healthy, balanced diet and maintaining an appropriate level of physical activity is a good way to lower cancer risk.

Bottom line

Curcumin and turmeric have many important biological functions, and laboratory studies suggest that they may help to prevent cancer in laboratory animals. Studies of curcumin in humans are still in the early stages, so more research is needed before we can say anything about a relationship between curcumin and cancer.

What you may have heard

Coffee consumption can increase your risk of cancer.

What science tells us

Epidemiological Evidence

Coffee drinking is not a cause of breast, pancreatic, or prostate cancer and may even reduce the risk of endometrial, head and neck, colorectal, and liver cancers (ACS) . There is also evidence that drinking coffee is linked to lower risk of insulin resistance and type 2 diabetes (ACS). Several epidemiological studies have shown that coffee consumption does not increase cancer risk (Zhao).

Laboratory Evidence/Supporting Evidence

Much of the concern about coffee consumption and cancer comes from the fact that coffee can contain a chemical called acrylamide, which is formed during the roasting process. Acrylamide has been shown to cause cancer in animals exposed to very high doses (ACS). These studies have concluded that coffee consumption does not cause cancer in mice (IARC).

IARC Carcinogen Classification:

Group 3 (Not classifiable as to its carcinogenicity to humans)

How to reduce your risk

There appear to be health benefits to drinking coffee. If you are worried about acrylamide exposure, you could reduce and limit the amount of food you eat that is cooked at high temperatures (during frying, roasting, and baking) for longer periods of time (ACS).

Bottom line

Coffee drinking is linked with a lower risk of endometrial, head and neck, colorectal, and liver cancers. Coffee drinking may also reduce the risk of insulin resistance and type 2 diabetes.

What you may have heard

Ketchup contains high-fructose corn syrup and MSG for flavoring and sweetness.  You may have heard these ingredients cause cancer.

What the science tells us

Numerous studies have shown that high-fructose corn syrup is harmful to your health, increasing your risk of weight gain, type 2 diabetes, metabolic syndrome, and high triglyceride levels.

Epidemiological Evidence

Excessive consumption of high-fructose corn syrup is also linked to obesity and an increased risk of colon cancer (Goncalves et al.).

While MSG has not been shown to increase the risk of cancer, studies have linked MSG consumption to obesity, central nervous system disorders, liver damage, and reproductive malfunctions (Niaz et al.).

Laboratory Evidence/Supporting Evidence

One study conducted on mice studied the effects of high-fructose corn syrup consumption. Researchers found that there was excess weight gain and the presence of tumors, indicating that fructose might affect tumor growth (NCI).

IARC Carcinogen Classification:

Not classified.

How to reduce your risk

Avoid products, including ketchup, that contain high-fructose corn syrup and MSG. Eat ketchup in moderation to reduce your health risks.

Bottom line

Eating ketchup itself does not appear to cause cancer. However, high consumption of high-fructose corn syrup, a key component in ketchup, is linked to obesity and an increased risk of colon cancer. While there are no direct links between cancer risk and MSG, there are other harmful health effects that should be considered when eating ketchup.