What is aflatoxin?

Aflatoxin is a naturally occurring contaminant produced by mold, particularly Aspergillus flavus and A parasiticus. These molds grow on crops, especially peanuts, tree nuts, corn, wheat, and seed oils (i.e., cottonseed) that are stored under conditions of warmth and humidity.

Does aflatoxin cause cancer?

Aflatoxin B1 has been classified as a known human carcinogen and is known to cause liver cancer in animals. Aflatoxins may also be associated with liver cell cancer in humans in Africa and Asia where peanuts are a dietary mainstay. Recent research has shown a strong association between long-term dietary aflatoxin exposure in conjunction with hepatitis B (a viral infectious disease of the liver) and increased rates of liver cancer.

How and where are people exposed?

Aflatoxins are widespread in nature. The Food and Drug Administration permits low levels of exposure to aflatoxin, believing that limited exposures over a lifetime are not dangerous. Humans are exposed to aflatoxins by ingesting contaminated foods. The FDA considers aflatoxin an “unavoidable contaminant.” Even with food supply monitoring of aflatoxins, concern remains over the effects of long-term dietary exposures to this toxin.

Can I still eat peanuts and peanut butter?

The FDA does test for aflatoxins in certain foods but permits low levels because these toxins are thought to be unlikely to cause disease with low-level exposures over a lifetime. Peanut butter and peanuts are more stringently tested and controlled in the U.S., since aflatoxins are commonly found on these food items and their consumption is widespread in this country. Although levels vary, the lowest levels of aflatoxin are found in brand name peanut butters found at grocery stores. Eating peanuts and peanut butter in moderation remains acceptable.

How can I reduce my risk of aflatoxin exposure?

Buy only major brands of nuts and nut butters, such as peanut butter, from reputable distributors. Do not store nuts for prolonged periods of time and throw away nuts that have become moldy, discolored or otherwise irregular.

Where can I get more information?

For more information, please refer to the following documents, which were used as sources for this fact sheet:

• Aflatoxins in Your Food – and the Effect on Your Health, Environmental Health and Safety Online, retrieved February 15, 2005, from Environment, Health and Safety Online
• Aflatoxin, USDA Grain Inspection, Packers and Stockyards Administration (GIPSA), retrieved November 2007, from the USDA Risk Management Agency.
• Aflatoxins: Occurrence and Health Risks, Cornell University, Department of Animal Science, retrieved February 15, 2005, click here

New Study Finds increased Risk of Fatal Lung Cancer in Workers and in Persons Living Near Asbestos Production in Italy. Read the report.

What is asbestos?

Asbestos is a generic name for six naturally occurring fibrous silicate minerals that are mined for commercial use. Asbestos has been widely used in the United States, but its use is on the decline. The National Toxicology Program declared asbestos a known human carcinogen in 1987 in its first report on human carcinogens.

What diseases are caused by exposure?

Asbestos exposure is associated with a number of diseases. Asbestosis, a chronic fibrous process in the lungs, was first noticed in naval shipyard workers exposed to asbestos. Mesothelioma, a tumor of the lining of the lungs or abdominal cavity that carries a particularly poor prognosis, and lung cancer are caused by inhalation exposure to asbestos.

How and where are people exposed?

The primary route of exposure is direct inhalation of asbestos particles, often on the job. For example, workers who renovate buildings with asbestos in them may become exposed when they inhale asbestos particles from insulation, tile, or other building materials that they are removing or installing. In addition, exposed workers can bring asbestos fibers home on their clothing, thus exposing the people with whom they live. Although its use is on the decline, asbestos has been widely used in the United States in such items as brake linings, insulation, and other building and industrial products. The majority of asbestos exposures occur among workers in the construction and asbestos manufacturing industries, but asbestos is also still used in brake linings. Consequently, employees in the automotive industry who work with brake linings also run the risk of asbestos exposure. Many older homes and other buildings, including schools, contain asbestos, thereby creating the potential for exposure among other groups of people as well.

Is there a safe level?

There is no known safe level of asbestos.

How do I know if I am exposed?

Asbestos fibers can be detected in urine, feces or mucus. A chest x-ray cannot detect fibers but can detect early fibrotic changes in the lungs caused by asbestosis. Mesothelioma and lung cancer can develop as many as thirty years after working with asbestos.

What can I do to avoid exposure?

Avoid working with asbestos and asbestos-containing products. If it is necessary to manipulate or work with asbestos, appropriate precautions including the use of protective equipment, a wet process, and adequate ventilation should be taken under the guidance of a professional.

Where can I get more information?

• Environmental Protection Agency
• National Toxicology Program, Report on Carcinogens, Eleventh Edition
• National Institute for Occupational Safety and Health
• The Ottowa Citizen: Canada exporting ‘misery’ of asbestos: Indian MD | December 15, 2007 

Until very recently, cancer prevention has largely focused on early diagnosis and treatment, also known as secondary prevention. By the time secondary prevention becomes necessary, the disease in question has already taken hold within an individual, and doctors just want to lessen its impact by finding it and treating it early. Alternatively, primary prevention is the practice of avoiding the causes of a disease in order to prevent getting it in the first place. Not nearly enough attention has been paid to primary prevention of cancer, but we do know some things you can do to reduce the chance that you will develop cancer during your lifetime. Read on to find out about 12 things you can do to avoid cancer.

Avoid smoking, overeating, and overdrinking, and keep moving. Take the stairs instead of elevators; find a form of exercise you like and commit to doing it with a friend. Plan to walk instead of drive. When driving, stick with the speed limit to save lives, save energy and reduce cancer-causing pollution; speed kills, pollutes and fuels terror.

Use x-rays and other radiation sparingly and keep a record of all x-rays. The excessive use of x-rays in infants and children may be one of the reasons more young people (those under 40 years of age) are getting cancer and can also contribute to cancer in adults.  Earlier this year, the American College of Radiology advised against unnecessary and excessive use of diagnostic radiation in children for this very reason.  Before ordering x-rays doctors should carefully weigh the risks and benefits of using MRI, or ultrasound, technologies that do not involve radiation.

Unless someone in your immediate family has had  breast cancer before menopause, hold off getting your first mammogram until at least age forty, or until your doctor advises you start having them—and then have them done sparingly. Mammography does not prevent breast cancer, but can reduce deaths from the disease in post-menopausal women. It is also important to have regular physical exam of breasts by a health professional.

Use hormones sparingly. Lifetime use of hormones affects cancer risk. Consider alternatives to chemical contraception such as IUDs and condoms (which also protect against sexually transmitted disease). Avoid long term use of medications that contain hormones, including hormone replacement therapy.

Test your basement for radon and if you live in an area with uncertain water quality, use a simple filter. An invisible gas, radon can seep into homes from the ground and increase the risk of lung cancer. It can easily and inexpensively be remedied.

Do not consume food and beverages that contain aspartame. Sweeten your food with good old-fashioned sugar or honey, or stevia instead. Despite having FDA approval, aspartame, the sugar substitute, was never given a green light by scientists—all were concerned about its potential to cause cancer.  New independent studies raise further concerns about its long term safety.

Use cell phones with an earpiece and speakerphone so the phone itself is not held up against your head. Children should not use cell phones. Studies claiming that there is no link between cell phone use and brain cancer were not conducted on people who used cell phones as much as the average person today. Cell phones emit low doses of microwave radiation that destroy rat brain cells and memory and reach one inch into the human brain. While British authorities recommend that children not use cell phones at all, some American firms are pushing phones for five year olds.

Buy local foods in season from farmers who use fewer pesticides. Use omega-3-fatty acid supplements free of pollutants and eat a diverse diet, rich in vitamin D, calcium and fiber.

Don’t put anything on your baby’s skin that you can’t eat. The materials that create “no more tears” in baby shampoo are banned in several countries, because they cause cancer in animals. In some cases lotions used on the heads of African-American babies caused development of breasts and pubic hair. The FDA has no authority to regulate any of these harmful compounds in personal care products, unlike the European Union.

Look under your sink and read the labels on your cleaning products—in general, the fewer ingredients they have, the better for you they are. Baking soda, vinegar, lemon juice, and toothpaste can be used to clean most things around the home. Some room deodorizers and mothballs contain carcinogens.

Don’t microwave anything in plastic, no matter what the directions say. Some plastic chemicals can leach into food.

Unlike nearly all industrial nations of the world, America and Canada have not banned asbestos. Before doing home renovations and repair of attics, roofing, ceiling and flooring tiles, find out if they contain asbestos and hire certified contractors if they do. Zonolite attic insulation and some forms of kitty litter contain asbestos-related materials. Half of all people with a rare form of cancer thought to be uniquely tied with asbestos called mesothelioma have no known workplace contact with asbestos.

Through leading a healthy life and avoiding certain known carcinogens, it is possible to reduce your lifetime risk of developing cancer. It is true that much remains to be learned about the environmental causes of cancer. While researchers continue to explore the causes, we can use what is already known to start practicing cancer prevention today. 

Why is drinking water safety important?
Water is essential to support human life, and as such, the safety of drinking water is of significant importance to all people. After all, people cannot survive without adequate clean water. The Centers for Disease Control and Prevention estimates that each year a million Americans will become infected with water-borne pathogens and a thousand will die. Most cases are isolated, but outbreaks do occur. An outbreak of cryptosporidium in Milwaukee occurred in 1993, killing over 100 people and infecting 400,000 others. This outbreak was caused by contamination of the public water supply. The issue of drinking water safety becomes even more important in people who have weakened immune (disease-fighting) systems. The United States has come a long way toward making its drinking water supply clean and safe, but the current mechanisms for disinfection and filtration cannot remove every substance that might do the body harm, especially if the body’s immune system is weakened.

Are there groups of people at higher risk for water-borne diseases?
The immune system serves to protect people from disease. Consequently, people who have problems with their immune systems are more susceptible to disease. These people include cancer and transplant patients undergoing immunosuppressive therapy, people with HIV/AIDS, and people born with immune system deficiencies. The elderly, children, and pregnant women may also be at increased risk of water-borne infections.

What is cryptosporidiosis?
Cryptosporidium enteritis, also known as cryptosporidiosis, is an infection of the small intestine with a parasite, cryptosporidium, found in water contaminated with human or animal feces. Symptoms of cryptosporidiosis include diarrhea, abdominal cramping, nausea, and fever. While infection with cryptosporidium in most people is not severe, infection in immunocompromised individuals can be quite dramatic with resulting malnutrition, dehydration, wasting, and even death. Outbreaks of cryptosporidiosis occur from time to time and may be associated with contaminated public water supplies.

If I am worried about cryptosporidium, what can I do?
Cryptosporidium is a hardy species and can survive the typical methods of disinfection employed by public water suppliers. Boiling water is the most effective way to kill cryptosporidium. Bringing water to a full boil for one minute is sufficient. Alternatively, a point-of-use water filter may be used. The filter must remove particles measuring 1 micrometer or less in diameter to be effective against cryptosporidium. Bottled water may be a reasonable alternative, but the quality of bottled water varies. Where the water originated, microorganisms in that water, and water treatment methods used prior to bottling vary from brand to brand. In the case of a local or regional outbreak, the health department or other health or government agency typically issues a boil water advisory.

Where can I get more information?
For further information on alternate sources of water for immunocompromised individuals, refer to the Environmental Protection Agency guidance document entitled “Safe Drinking Water – Guidance for People with Severely Weakened Immune Systems” From the United States Environmental Protection Agency.

For further information on drinking water safety, please refer to the following sources:

Environmental Protection Agency

EPA Safe Drinking Water Hotline | 800-426-4791

Safe Drinking Water – Guidance for people with severely weakened immune systems

Drinking Water and Health: What You Need to Know

All public water suppliers must publish an annual drinking water quality report. The report should be mailed to you annually but may also be accessed via the following Web resources:

• EPA Local Drinking Water Information
• Allegheny County Health Department 

Estrogen is a natural female hormone produced by the ovaries in women and the testes in men. Estrogen is found in much higher concentrations in women’s bodies. It stimulates puberty, regulates the menstrual cycle and breast development, plays a crucial role in pregnancy, and is also necessary to maintain strong, healthy bones. The level of estrogen present in a woman’s body varies depending on her age and monthly cycle. During certain times of the month, estrogen levels are higher or lower. Estrogen levels decrease dramatically after menopause, which can cause thinning of the bones or osteoporosis. In addition to the estrogen produced by their own ovaries, many women are exposed to synthetic or man-made estrogens through oral contraceptive (birth control) pills (OCs), transdermal patches, hormone replacement therapy (HRT), and vaginal creams and rings. The two most common medical uses for synthetic estrogens are birth control and hormone replacement therapy taken after menopause.

What are estrogen-mimicking compounds?

Some substances contain compounds that are structurally similar to estrogen on a molecular level. One type, phytoestrogens, is naturally occurring and found in plants. Other substances in the environment, including some chemicals, have estrogen-like properties and are considered estrogen mimickers. These compounds can have estrogen-like effects on plants and animals, including humans. Currently, there is a significant research effort to determine the health effects of estrogen-mimicking compounds, especially in terms of reproductive outcomes and cancer risk.

Does estrogen cause cancer?

Research has linked estrogen to cancers of the breast, endometrium (uterus), and cervix. Known risk factors for breast cancer include conditions that cause women to be exposed to higher estrogen levels over their lifetimes, such as early menarche (beginning of the monthly period at a young age), late menopause, having children after age 30 or having no children. Findings from research studies attempting to link oral contraceptives containing estrogen to breast cancer have not yielded clear results. Some studies show an association, while others do not. On the other hand, the Women’s Health Initiative showed a clear increase in breast cancer in women who took combined HRT (estrogen and progestin). It is not clear whether women who take estrogen replacement therapy (estrogen alone without progestin) have a higher risk as well, although it appears they do not. Scientific studies have consistently and clearly shown that prolonged estrogen exposure increases the risk of endometrial (uterine) cancer. According to some studies, long-term use of oral contraceptives containing estrogen may increase the risk of cervical cancer. Oral contraceptives may also increase the risk of certain malignant liver tumors and are known to cause hepatic adenomas, rare but benign liver tumors that do not spread but can cause bleeding. Conversely, studies have revealed that taking oral contraceptives actually reduces the risk of ovarian cancer.

What is the Women’s Health Initiative (WHI)?

The Women’s Health Initiative is a large study of 16,000 women ages 50 through 79, which revealed that women on HRT ran a higher risk of heart disease, stroke, breast cancer, and blood clots. The study was stopped in July 2002 when researchers realized that combined HRT (estrogen and progestin) had significantly more risks than benefits. Based on these findings, doctors no longer recommend HRT as the primary form of prevention and treatment of osteoporosis or post-menopausal symptoms.

Should I stop taking birth control pills or HRT?

If you are concerned about taking products containing estrogen, consult with your physician. The decision should be made based on a thorough review of your personal and family medical histories and what risk factors you have for cancers of the breast, uterus, and cervix. Your personal and family history of heart disease and stroke must also be considered, since recent research clearly shows that HRT increases the risk of cardiovascular disease. Deciding to take OCs or HRT is a personal as well as a medical decision. For many women, the need for birth control or regulation of the menstrual cycle may outweigh the potential risks of taking oral contraceptives. Some women have such severe menopausal symptoms that they may choose to take HRT as a short-term treatment. Long-term administration of HRT, as in the prevention and treatment of osteoporosis, is not recommended primarily due to the increased risk of cardiovascular disease. As always, any medical decision should be made after a thorough discussion with a physician where the risks and benefits based on an individual’s personal situation are fully explained.

Where I can get more information?

• National Cancer Institute | Cancer Facts – Oral Contraceptives and Cancer Risk
• Menopausal Hormone Use: Questions and Answers
• Center for Bioenvironmental Research at Xavier and Tulane Universities | e.hormone – Your Gateway to the Environment and Hormones 

Radon is a toxic, radioactive gas with no color, odor or taste that forms from the normal decay process of uranium, which is present in most rocks and soil. Uranium slowly breaks down to other products, including radium, which then breaks down to radon. This decay process produces alpha, beta, and gamma radiation.

Some of the radon moves to the soil surface and enters the outdoor air or enters a house or building through cracks in the foundation, while some radon remains below the soil surface and enters the groundwater. Radon levels in the soil range from a few hundred to several thousand pico Curies per liter (pCi/L). The amount of radon that escapes from the soil to enter the house depends on the weather, soil porosity, soil moisture, foundation integrity, and the suction within the house.

What diseases are caused by radon exposure?

Radon is the second leading cause of lung cancer after smoking, and in fact, concurrent exposure to radon plus smoking leads to an even higher risk of lung cancer. Lung cancer generally occurs after many years of exposure.

How and where are people exposed to radon?

People are most often exposed to radon through inhalation of contaminated indoor air. According to the Environmental Protection Agency, nearly one in fifteen homes has an elevated level of radon. Outdoor air can contain radon as well but in smaller concentrations. Drinking water may contain radon, although usually in lesser concentrations than in air. Radon can leach from the soil into underground well water and then enter a house or building through the water supply or escape from soil as a gas and enter the house or building through cracks in the foundation. Occupational exposures to radon, such as found in underground uranium miners, lead to a higher risk of disease.

Is there a safe level of radon?

The EPA recommends a level of less than 4 pico Curies per liter (pCi/L) of radon in indoor air; however, there is no established safe level of radon. The EPA recommends remediation (taking action to lower the level) immediately if the radon level is greater than 4 pCi/L. Furthermore, EPA suggests that homeowners consider fixing radon levels between 2 pCi/L and 4 pCi/L to maintain a radon level of below 2 pCi/L. The average radon level in homes in the United States is 1.3 pCi/L, but certain parts of the country have higher average radon levels than others.

How do I know if I am exposed to radon?

You can find out if you are being exposed to radon by having the air in your home tested by a certified radon testing service. Water, a less significant source of radon, can also be tested. Routine medical testing does not detect radon in the human body. Your doctor will not be able to tell by examining you or testing your blood if you have been exposed to radon.

If my home’s radon level is too high, what can I do?

If the radon level in your home is 4 pCi/L or higher, contact a certified radon remediation service right away. Since no safe level of radon exists and radon levels less than 4 pCi/L still carry a risk, it is advisable to remediate levels below 4 pCi/L in order to achieve a level of 2pCi/L or less.

Where can I get more information on radon?

The following are excellent sources for information on radon, testing, and remediation:

• Environmental Protection Agency
• A Citizen’s Guide to Radon | The Guide to Protecting Yourself and Your Family from Radon | PDF
  
• Pennsylvania Department of Environmental Protection | Radon Division | 717-783-3594 or 800-23RADON (800-237-2366)

Source: National Cancer Institute (NCI) | Cigarette Smoking and Cancer: Questions and Answers | November 2007

Key Points

• Cigarette smoking causes 87 percent of lung cancer deaths and is responsible for most cancers of the larynx, oral cavity and pharynx, esophagus, and bladder.
• Secondhand smoke is responsible for an estimated 3,000 lung cancer deaths among U.S. nonsmokers each year.
• Tobacco smoke contains thousands of chemical agents, including over 60 substances that are known to cause cancer.
• The risk of developing smoking-related cancers, as well as noncancerous diseases, increases with total lifetime exposure to cigarette smoke.
• Smoking cessation has major and immediate health benefits, including decreasing the risk of lung and other cancers, heart attack, stroke, and chronic lung disease.

Tobacco use, particularly cigarette smoking, is the single most preventable cause of death in the United States. Cigarette smoking alone is directly responsible for approximately 30 percent of all cancer deaths annually in the United States. Cigarette smoking also causes chronic lung disease (emphysema and chronic bronchitis), cardiovascular disease, stroke, and cataracts. Smoking during pregnancy can cause stillbirth, low birthweight, Sudden Infant Death Syndrome (SIDS), and other serious pregnancy complications. Quitting smoking greatly reduces a person’s risk of developing the diseases mentioned, and can limit adverse health effects on the developing child.

Tobacco Smoking and Cancer

Since the early 1950s a large number of studies have shown correlations between smoking history and cancer of the lung as well as other organs. Evidence linking smoking with lung and other cancers has been obtained from many epidemiological studies. Many carcinogens have been found in tobacco smoke, and cigarette smoke condensate produces cancer in animals. Cancer in general and smoking induced cancer in particular usually occurs from 15 to 30 years after exposure to the carcinogen begins. Since the end of World War II, the number of deaths caused by tobacco smoking have increased sharply, because of heavy smoking during the 1930s, 40s and 50s. Tobacco smoking is estimated to be responsible for at least 30% of all cancer deaths in the U.S. and Europe. Cancer caused by tobacco smoking could reach epidemic proportions in developing countries in the near future. Since smoking causes death from heart disease, other lung diseases and other diseases, tobacco smoking can be estimated to cause approximately 5 million deaths a year worldwide, a figure which is expected to increase to 10 million deaths a year by 2030. Tobacco smoking caused 100 million deaths in the 20th century, (about twice the total number of civilian and military casualties from World War II), but could reach 1 billion deaths in the next century, unless something is done to decrease the number of people exposed to cigarette smoke. About one half of all lifetime tobacco smokers will die because of their habit.

The evidence shows that tobacco smoke is a carcinogenic mixture that can cause cancer in many different organs in human beings. Smoking is also highly synergistic with other environmental carcinogens. For example, the incidence of lung cancer among uranium miners who also smoked was extremely high. The same pattern has been seen for asbestos workers and many other groups of people exposed occupationally to chemical carcinogens. One of the most informative studies relates to the incidence of lung cancer as a function of gender. Historically this has been a predominantly male disease. However, after World War II women began to smoke with equal frequency to men. The frequency of lung cancer in women began a steep upward trend just 20 years later, paralleling the curve of smoking incidence. Lung cancer deaths now outrank breast cancer deaths as the leading cause of cancer mortality in women.

In 1986, the International Agency for Research in Cancer, an international organization that determines the carcinogenic potential of chemicals and materials, found that tobacco smoking was carcinogenic in humans (cigarette smoking was given a 1A classification, reserved only for those chemicals and processes that have been proven to be human carcinogens), and concluded that tobacco smoking caused cancers of the lung, renal pelvis, bladder, oral cavity, pharynx, larynx, esophagus, and pancreas. This judgment, reached by an international panel of medical and scientific experts was based on published data and incorporated consideration of bias or confounding factors, the presence of dose–response relationships, biologic mechanisms, and the consistency of findings from different independent investigations using different study designs, from different countries.

Since 1986, further evidence shows that smoking tobacco also causes cancer of the nasal cavity, paranasal sinuses, and nasopharynx; stomach; liver; kidney; cervix uteri; and adenocarcinoma of the esophagus and myeloid leukemia. Cancer can be caused by smoking cigarettes, pipes, and cigars. Cigar and pipe smoking causes cancers of the oral cavity, oropharynx, hypopharynx, larynx, esophagus, and lung. The idea that the risk of cancer from pipes and cigars is much less than that of cigarettes is not correct. Dose–response relationships have been found with the amount of cigar and pipe tobacco smoked.

Cigarette smoke contains an amazing variety and number of carcinogens; in fact, it would be hard to deliberately formulate a more carcinogenic mixture than cigarette smoke. In the gas phase are found several nitrosamines such as dimethylnitrosamine, urethane, formaldehyde, and vinyl chloride, all complete carcinogens. In the particulate phase are found the carcinogens benzopyrene, beta-naphthylamine, methylchrysene, benzofluoranthene, benzanthracene, and more than two dozen other aromatic hydrocarbons. Tumor promoters and cocarcinogens such as pyrene, naphthalene, catechol, phenols, methylindoles, methylcarbazoles, and others are also found in smoke. Besides these hydrocarbons, cigarette smoke contains carcinogenic metals such as nickel and cadmium and the radioactive element polonium 210. A large number of the constituents of smoke have proven positive in carcinogenic bioassays. An important class of chemical carcinogens, the nitrosamines, are produced in cigarette smoke from nicotine, the addictive agent.

Because tobacco smoke contains so many potent carcinogens of so many types, it is difficult to attribute the carcinogenicity of tobacco to any particular compound. The most likely situation is that various different combinations of carcinogenic compounds with different mechanisms of action act to produce malignant cancer. The active narcotic agent in tobacco, nicotine is chemically converted during curing, processing, and burning into a series of carcinogenic compounds called nitrosamines. These agents are tobacco specific; they are found in snuff and chewing tobacco as well as in cigarette mainstream and sidestream smoke. The nitrosamines NNN and NNK produce tumors in lung, nasal cavity, esophagus, and trachea, in rats, mice and hamsters. These agents require metabolic activation for their carcinogenic action; human trachea, lung, and other respiratory tissues have been shown to metabolically activate NNN and NNK, and they have been detected in the urine of smokers.

The presence of radioactive elements in cigarette smoke has been known since the 1960s. These elements include radium 226, radon-228, thorium-228, traces of other elements and polonium-210. Polonium-210 is the most abundant of these in smoke. It is an alpha emitter and is volatile at the temperature of a burning cigarette. Alpha radiation is an intense form of radioactivity known to be carcinogenic in animals and humans. Due to very low solubility, polonium-210 is retained and concentrated in lung tissue longer than other tobacco smoke constituents.

Mechanisms of Tobacco Carcinogenesis

Scientists have used biochemistry and molecular biology to investigate the mechanisms of tobacco carcinogenesis. Metabolites of chemical compounds present in tobacco, DNA adducts (a chemical form of attachment of a carcinogen to DNA), genetic mutations in the DNA, and alterations of chromosomes have all been identified in human beings in connection with tobacco smoking.

Carcinogenic compounds present in tobacco smoke, produce functional destructive mutations in a critical gene – p53, which is one of the most important cancer related genes. A specific pattern of mutations in the p53 gene has been identified as a molecular signature of lung cancer caused by tobacco smoking. DNA adducts of these same compounds are present in human tissues exposed to tobacco smoke. Tobacco smoke also contains arylamines, such as the potent carcinogen 4-aminobiphenyl, which causes bladder cancer. 4-Aminobiphenyl forms DNA-adducts in bladder cells in the urine and in bladder biopsies from smokers.

One of the most well known chemical carcinogens in tobacco smoke is benzo[a]pyrene and DNA adducts of this chemical have been found in the cervical tissues of smokers. Another famous carcinogen in tobacco smoke is benzene, a chemical known to cause leukemia. Smokers have increased cytogenetic damage of the type associated with effects of benzene.

The only good news about smoking is that individuals who stop smoking reduce their cancer risks dramatically. The earlier an individual stops smoking, the lower the risk of lung cancer, and all other causes of death by smoking. For example, the probability of getting lung cancer by age 75 for a man who starts smoking at age 18 drops from 16% to 6% if he stops smoking by age 50, and it drops all the way to 2% is he stops by age 30. It is therefore critical for public health to assist people in their efforts to stop smoking.

Non-smokers who breathe smoke (called sidestream smoke) from other people’s cigarettes (i.e., involuntary smoking) are exposed to the same carcinogens as smokers, although at much lower doses. Children of smokers have seven times the incidence of asthma and upper respiratory infections as children of nonsmokers.

For the past decade environmental tobacco smoke (ETS) or passive smoking, has been investigated as a cause of lung cancer. Recent definitive studies and reviews of many studies have used the nonsmoking spouses of smokers as the test group. Spousal exposure is well defined and has been validated using biochemical markers. Non-smokers who live with smokers are also more likely to mix socially with smokers. Other studies have used workplace exposure to ETS, which are more variable and therefore harder to study scientifically. The results from domestic exposure to ETS can be used to judge the risk from workplace exposure, depending on the exposure levels, which in some cases, such as in bars and restaurants can be extremely high.

In a recent meta-analysis and general review of all published studies on ETS and cancer, it was found that seven published studies showed a significant excess risk of lung cancer in the non smoking spouses of smokers. Other studies showed increased risks, but because the number of cases were small, they were not statistically significant. This problem can be overcome by meta-analysis, which combines all the studies into one large study. When this was done, the total combined relative risk of lung cancer from 37 different studies on women was 1.24 or 24%. This increased cancer risk was statistically significant, meaning that it was not due to chance or error. The risk of lung cancer from exposure to environmental tobacco smoke was the same for men and women, and did not depend on geographical location, or many other parameters.

A significant dose-response relation was seen between the number of cigarettes smoked by the husband and the risk of lung cancer in their non smoking wives. The risk increased by 23% for every 10 cigarettes smoked per day by the husband (88% if he smoked 30), and by 11% for every 10 years of exposure (35% for 30 years’ exposure). The risk of lung cancer from ETS was higher for squamous and small cell carcinoma (58%) than for adenocarcinoma (25%). Since smoking is more strongly related to squamous and small cell carcinoma than adenocarcinoma, this suggests that exposure to environmental tobacco smoke is equivalent to smoking at a low dose.

The high risk of lung cancer in non-smokers who live with smokers has been claimed to be an illusion caused by statistical or analytical errors called bias or confounding. Because of the growing social stigma attached to cigarette smoking, some smokers may say that they are non-smokers. This could lead to a bias called misclassification. These people would be more likely to develop lung cancer, and therefore lead to an over-estimate of the true risk of lung cancer in the test group of nonsmoking spouses of smokers. Other biases could come from dietary factors, and exposure to ETS in the control group. The degree of these biases have been estimated and taken into account in studies of ETS risk.

Adjustment of the observed relative risk of 1.24 for misclassification bias, dietary confounding and exposure to ETS in the control group gave a corrected final result of 1.26 or 26%. This is similar to the value obtained from extrapolation of the risk due to exposure to ETS using biochemical evidence. The chemicals nicotine and cotinine are formed from tobacco and excreted in the urine. In non smokers exposed to ETS, nicotine and cotinine concentrations are about 1.0% of those found in the urine of smokers. This suggests that non-smokers exposed to ETS have about 100 times less exposure to tobacco smoke than regular smokers. Assuming dose linearity, this would mean a 100-fold lower lung cancer risk for people exposed to ETS. Since smokers have a relative risk for lung cancer of about 20 (2000%), then ETS exposed non smokers should have a risk of about 20%, a value that is in close agreement with the observed value of 26%. This estimated excess risk of 26% corresponds to several thousand deaths per year in the U.S.

A larger and even more recent study than the one described above gave very similar results with a risk for ETS exposure of 25%. This study pooled data from 46 published papers including 6,257 lung cancer cases. In this study the non smoking husbands of women who smoked had an even higher risk (35%) than did non smoking wives of smokers. Similar conclusions were reached by studies that have examined the risk of lung cancer among non-smokers exposed to ETS in the workplace.

Public health measures to decrease exposure to ETS and to decrease smoking can save millions of lives. Medical history is full of other examples of non-medical interventions used to prevent disease and extend human life and well-being. Some examples include sewage treatment, sanitary conditions in health care, and removal of lead from paint and gasoline. Laws restricting smoking are in the same category as these examples. In cities around the world where antismoking laws have been enacted, hospital admissions for severe respiratory distress dropped dramatically. An interesting natural experiment was done in Helena, Montana. An antismoking law was enacted for Helena’s pubs and restaurants, and then 6 months later rescinded due to commercial pressure. For the six months of the ban, hospital admissions for a variety of illnesses including heart attacks dropped dramatically. When the ban was rescinded this measurable improvement in the health of the population was immediately reversed, and the rate of admissions went back to what it had been before the ban.

The effects of secondhand tobacco smoke cost the U.S. economy nearly $10 billion a year, ranging from medical bills to lost hours on the job according to an article in the Wall Street Journal. The article also states that this could encourage insurers to consider separate pricing for nonsmokers exposed to tobacco smoke.

The major health benefits of such laws can be tallied with respect to their effects on general cancer risk in the population. Such laws reduce exposure to ETS for both customers and employees. In addition, they encourage smokers to quit smoking and discourage people trying to quit from giving up. They also help to discourage young people from starting to smoke, one of the most important and difficult tasks in the anti-smoking campaign.

The general trend toward decreased smoking incidence in the U.S. and Western Europe, and the trend toward greater restrictions on smoking in public places have gone together in recent years. Anti-smoking laws are an important part of the general public health agenda, which seeks to improve and prolong each precious human life in our community.

• Additional information about cancer or tobacco use | 800–4–CANCER
• Help with quitting smoking | Smoking cessation quitline: 877–44U–QUIT
• Additional information on health risks of smoking available at Centers for Disease Control and Prevention’s Office on Smoking and Health (OSH) | 800–CDC–1311 (1–800–232–1311)