Risk Factors

Schizophrenia is the most common psychotic condition.

Age

Schizophrenia can occur at any age, but it tends to first develop (or at least become evident) between adolescence and young adulthood. Schizophrenia that is recognized in children is likely to be severe. Although the risk of schizophrenia declines with age, its incidence has been known to peak in those who are about 45 years old, and again in people who are in their mid-60s (mostly women). Late-onset schizophrenia that develops in the 40s is most likely to be the paranoid subtype with fewer negative symptoms or learning impairment. Such patients usually have functioned at a near-normal level until structural deficits in the brain break down.

Gender

• Men tend to develop schizophrenia between the ages of 15 - 24. Paranoid schizophrenia may be more common in men, and symptoms tend to be more severe.
• The onset in women is usually slightly later, between ages 25 - 34, and the symptoms tend to be less severe. The earlier a girl starts menstruation, the longer she is protected against schizophrenia. Schizophrenia is more severe during a woman's menstrual cycle when estrogen levels are low. Such findings and other evidence suggest that estrogen may have nerve-protecting properties. For example, the higher the estrogen levels in female patients with schizophrenia, the better their mental functions.

Intelligence

People with schizophrenia span the full range of intelligence. In fact, one study reported that a higher than expected number of people who develop schizophrenia had been intellectually gifted children. Research suggests, however, that a decline in IQ scores during childhood may be a sign of potential psychotic symptoms in adults.

Cultural and Geographic Factors

No cultural or geographic group is immune from schizophrenia, although the course of the disease seems to be more severe in developed countries. However, the content of delusions may vary depending on a person's culture. According to one study, European patients were more apt to have delusions of poisoning or religious guilt while in Japan the delusions were most often related to being slandered.

Socioeconomic Factors

Schizophrenia occurs twice as often in unmarried and divorced people as in married or widowed individuals. Furthermore, people with schizophrenia are eight times more likely to be in the lowest socioeconomic groups. According to a 2001 study, however, these findings are likely to be a result of schizophrenia rather than a cause. Nevertheless, low income and poverty increases the risk for delayed diagnosis and treatment, and such delays could lead to more severe disease in patients with fewer resources. Poverty may also increase exposure to biologic factors (such as infections or toxins) or social stressors that could trigger the illness in susceptible people.

Famine and Malnutrition

Prenatal malnutrition may also play a role in the development of schizophrenia. A 2005 study found that people who were born during times of famine were more than twice as likely to develop schizophrenia as those born during years of adequate food. The association between famine and schizophrenia illustrates how environmental and biologic factors are connected. Scientists think that malnourished mothers may not get enough folate in their diet. Folate is a micronutrient important for genetic processes. Folate deficiencies may cause genetic mutations in the developing fetus that can lead to schizophrenia.

Other Factors Associated with Schizophrenia

Being Left- or Mixed-Handed. The rate of left-handedness or mixed-handedness is significantly higher among patients with schizophrenia than the general population. This suggests that some neurologic pattern that may be responsible for each. (A large minority of the population is non-right handed and very few of these people develop schizophrenia.)

Abnormal Olfactory Bulbs. Studies suggest a problem in the sense of smell among patients with schizophrenia. One study reported abnormally small olfactory bulbs in patients with schizophrenia. Olfactory bulbs are nerve centers in the brain that regulate the sense of smell.

Obsessive-Compulsive Disorder. Obsessive compulsive disorder (OCD) affects a significant number of schizophrenic patients. OCD is an anxiety disorder marked by obsessions (recurrent or persistent mental images, thoughts, or ideas) that may result in compulsive behaviors, repetitive, rigid, and self-prescribed routines that are intended to prevent the manifestation of the obsession. Some experts believe the behaviors exhibited in the disorder may actually be protective in people with schizophrenia in early stages. Behavioral and Motor Problems in Childhood. Children who later develop schizophrenia often suffer from the following certain problems, including excessive shyness or minor early physical and motor-control problems. Such problems are so common, however, that their presence without any other risk factors is no cause for concern.

Father’s Age. According to some studies, the older a father is when a child is born, the greater the risk is for schizophrenia in his offspring, perhaps because of a greater chance of genetic mutations in the sperm that can be passed on. In one study, children of fathers who were 50 years old or more or faced a three-fold risk for schizophrenia compared to children of fathers who were 25 or younger.

Epilepsy. A family history of epilepsy increases the chance for developing schizophrenia or schizophrenia-like psychosis. Scientists think that epilepsy and schizophrenia may share similar genetic or environmental factors.

Review Date: 12/21/2006
Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.

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