Potential causes
Environmental Factors
As it is the case with other complicated diseases, there are probably several factors that lead to the development of schizophrenia, some genetic and some environmental.
In terms of suspicious factors in the environment (the world around us) that may influence whether or not we develop schizophrenia, the list is growing. At least fifty separate investigations have identified a relationship between early environmental factors and schizophrenia (Thomas McNeil, Human Brain Informatics, www.hubin.org). They include, but are not limited to, exposure to lead, older mothers, obstetric complications (problems with childbirth), early infections (especially influenza), maternal stress during pregnancy (including starvation), birth and early childhood in urban settings, birth in winter or early spring, excessive stress in our younger years, and drug use in our teenage years. There has also been some speculation that immune disorders may play a role.
The combination of these environmental factors and our genetic risk represents our ultimate risk. It appears that relatively high risk environmental factors combined with low genetic risk may produce results similar to relatively low risk environmental factors combined with high genetic risk. High risk environments and high genetic risk produces the most dramatic affect on our susceptibility to schizophrenia.
How do environmental factors increase our risk? The consensus between clinicians and researchers is that they probably represent types of damage to the brain. The injuries may amount to changes in brain structure and biochemistry. While these changes may occur early in life, their results may not appear until sometime later. The foundation for developing schizophrenia may be present, but the disease is dormant until we reach puberty and begin to mature. This is a time when hormones begin to have powerful influences on the development of the body and the brain as we mature. Previous damage may have involved the development of certain nerves, which in turn may influence the production of enzymes or other biochemicals, the establishment of connections between nerves, or change how sensitive nervous tissue is to the environment or to biochemicals within the brain.
What can we do about the limited knowledge we have about inheritance and suspected environmental factors? It is probably helpful to accumulate whatever reliable family history we can about the presence of mental illness in our family. This applies not only to the presence of schizophrenia, but to other mental illnesses as well. A positive family history for all other mental illnesses, except substance abuse diagnoses, may increase our risk for schizophrenia (The British Journal of Psychiatry 181:s19-s25 2002).
Suicide in other family members is clearly correlated. This information will be useful to any treating physician. If schizophrenia or a combination of mental illnesses are particularly prominent in our family tree, it may be useful to consult with a genetic counselor who can more accurately calculate relative risk, if that information is desired for family planning. In those cases, some medical screening is available beyond what would otherwise be done. Such tests, those that may identify specific genetic markers for schizophrenia, will likely assume greater importance in the future as we see advances in gene therapy. The study of specific gene products (the molecules that those genes produce) will undoubtedly help scientists develop better medications.
The current knowledge we have about environmental risk factors for schizophrenia may at least cause us to change some of our behaviors. Regardless of how strong the specific links are between schizophrenia and some environmental factors, it seems wise to reduce any that we can.
Avoiding exposure to environmental toxins during pregnancy is common practice. Many physicians who treat women of childbearing age recommend exposure to the fewest number of prescription or over the counter medications as possible. Alcohol should be avoided entirely, since we know that it can produce injury to the central nervous system, and there is no clearly established dose that represents “safe” exposure.
A visit to the websites of the CDC (Centers for Disease Control), The American Lung Association, Mayo Clinic College of Medicine, or 1.drugaware.com will make the reasons why tobacco products should also be avoided painfully clear. Tobacco smoke contains more than 4,000 chemicals, many of which are clearly poisons. A few that deserve special mention are hydrogen cyanide, nicotine (which is itself a potent poison), carbon monoxide, tar, nickel, cadmium, and arsenic. In addition to their direct additive toxic affects, which lead to lower birth weights, premature births and breathing problems (including asthma), some of these agents reduce the supply of oxygen and nutrients to the fetus.
It is clearly understood that the risks for a number of problems increases with the age of the mother. Avoiding stress to the extent that this is possible makes sense. Good nutrition and regular prenatal care are essential for every pregnancy. It is probably not very practical, although not impossible, to avoid giving birth to our children in winter or early spring or ensuring that they are born in rural, rather than urban areas.
Doing whatever we can to reduce the chances that they will abuse drugs as teenagers can not be overemphasized. Discouraging them from using tobacco products would be the best place to start. According to the 2005 figures from the National Survey on Drug Use & Health, smoking among all age groups is slowly declining. However, tobacco is first used at an earlier age, and it continues to be the “entry level” drug that is used at the earliest age. The most sobering finding comes from the Substance Abuse and Mental Health Services Administration, U.S. Department of Health and Human Services.
A review of this data indicates that “Youths age 12-17 who smoke are more than 11 times as likely to use illicit drugs and 16 times as likely to drink heavily as youths who do not smoke.”
(Sources: The author’s knowledge base, unless otherwise noted.)
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