Children, Cancer & The Environment
By identifying elements in the environment that contribute to cancer, we can take steps to eliminate them and protect our children and ourselves.
It's always heartbreaking when cancer strikes a child. Yet medicine has made huge strides in treating this disease, and many young victims now survive.
But can we prevent childhood cancer from occurring in the first place? In the future, the answer may sometimes be yes. That's because scientists now believe that many childhood cancers are caused by environmental agents -- that is, by causes outside the body. Environmental factors, unlike such factors as heredity, can theoretically be controlled. So, as scientists learn more about the environmental causes of cancer, parents have more opportunities to shield their children. Of course, parents can't protect their children from every possible hazard. So NRDC is working to decrease and eliminate some of the chemicals that may contribute to childhood cancer.
Read on to learn more about some of the suspected environmental causes of childhood cancer and how you can reduce the risks to your own children. For more information on childhood cancer in general -- rates, common types and effects -- check out the Q & A.
Linking Environmental Factors with Childhood Cancer
In some cases, researchers have found direct links between environmental agents and cancer in children. For instance, there is proof that X-rays and certain chemicals used for chemotherapy can cause leukemia, and that exposure to the synthetic hormone DES (diethylstilbestrol) before birth can cause vaginal cancers in young women.
More often, scientists have indirect evidence. When it comes to disease, there are few "smoking guns" -- unambiguous reasons explaining why people get sick. Instead, there are correlations, or associations, between certain factors and a given disease. In the case of childhood cancer, studies increasingly show correlations between certain environmental agents and rates of the illness. Today, most scientists believe that environmental factors cause or contribute to many cancers in children. The environmental agents linked to these cancers include pesticides, radiation, solvents, electromagnetic fields, paints, chemicals associated with the use of vehicles, metals and secondhand tobacco smoke.
Additional evidence comes from variations in rates of common childhood cancers in different parts of the world, which also suggest that environmental factors contribute to the disease. Another strong indication comes from studies of childhood cancer in identical twins, who have identical genetic make-ups. If these cancers were primarily caused by genetics, almost any time one identical twin got cancer, we'd expect to see it in the other twin as well. But that only sometimes occurs. It's likely, therefore, that heredity is not the major factor behind most of these cancers. Instead, environmental factors probably make one twin sick.
Many scientists believe, however, that environmental agents and genetic factors may turn out to be intertwined. It may be that some children inherit a predisposition to cancer, which environmental exposures later activate. Or, hereditary factors may make it hard for some children to withstand certain environmental exposures.
Critical Periods for Environmental Exposures
Many people assume that the vulnerability to cancer begins only at birth, but that's not true. A great deal of evidence indicates that childhood cancers may originate earlier -- even before children are conceived. In fact, there are three periods when environmental agents can cause cancer in children: before conception, during pregnancy and after birth.
How can environmental exposures affect children even before they're born? By affecting their parents' sperm or eggs. For instance, some studies have found that fathers who are exposed on the job to such chemicals as solvents or pesticides are more likely to have children who develop cancer. The exposure may affect the sperm in a way that predisposes the children to cancer later in life.
During pregnancy, many hazardous chemicals easily cross the placenta. The fetus is very vulnerable to these exposures. Sometimes, they cause problems that are immediately obvious, such as miscarriages or birth defects. At other times, however, the health effects -- including many childhood cancers -- don't show up until later in childhood.
After birth, of course, children remain susceptible to environmental exposures, which they may now receive directly. In fact, they are particularly vulnerable to these direct exposures. For one thing, children's immature bodies cannot yet detoxify and eliminate many contaminants. In addition, compared with adults, their small bodies take in proportionally greater volumes of air, food and liquid. And children often have greater contact with environmental contaminants because of their behavior: they spend more time on the floor, for instance, and put many things in their mouths.
last revised 4/10/2002
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