No season-of-birth effect in schizophrenic patients from a tropical island in the Southern Hemisphere

Systematic review and meta-analysis: Season of birth and schizophrenia risk

OBJECTIVE

Winter birth has been hypothesized to be associated with increased schizophrenia risk for nearly a century. Major hypotheses regarding the potential etiological risk factors for schizophrenia such as vitamin D deficiency and virus exposure in utero are predicated based on the observation that risk of schizophrenia is higher in children born in winter months.

METHODS

We conducted a systematic review and meta-analysis to examine the association between season and month of birth and risk of schizophrenia. We further investigated this relationship stratified by hemisphere.

RESULTS

Forty-three studies spanning 30 countries and territories and 440,039 individuals with schizophrenia were included in this meta-analysis. Winter births were associated with a small but statistically significant increased risk of schizophrenia (OR 1.05, 95 % CI 1.03-1.07, p < 0.0001) and summer births were associated with a small but statistically significant decreased risk of schizophrenia (OR 0.96, 95 % CI 0.94-0.98, p = 0.0001). Stratified subgroup analysis demonstrated no significant difference between hemispheres in the risk of schizophrenia for either winter or summer births.

CONCLUSIONS

Analysis using birth month data demonstrated a clear seasonal trend towards increased risk of schizophrenia being associated with winter birth months and decreased risk of schizophrenia in summer-to-fall months in the Northern but not Southern Hemisphere. These data suggest a small-but-substantial increased risk of schizophrenia in winter birth month. Further research needs to examine potential etiologic causes for this association.

Viral infection, inflammation and schizophrenia

Schizophrenia is a severe neurodevelopmental disorder with genetic and environmental etiologies. Prenatal viral/bacterial infections and inflammation play major roles in the genesis of schizophrenia. In this review, we describe a viral model of schizophrenia tested in mice whereby the offspring of mice prenatally infected with influenza at E7, E9, E16, and E18 show significant gene, protein, and brain structural abnormalities postnatally. Similarly, we describe data on rodents exposed to bacterial infection or injected with a synthetic viral mimic (PolyI:C) also demonstrating brain structural and behavioral abnormalities. Moreover, human serologic data has been indispensible in supporting the viral theory of schizophrenia. Individuals born seropositive for bacterial and viral agents are at a significantly elevated risk of developing schizophrenia. While the specific mechanisms of prenatal viral/bacterial infections and brain disorder are unclear, recent findings suggest that the maternal inflammatory response may be associated with fetal brain injury. Preventive and therapeutic treatment options are also proposed. This review presents data related to epidemiology, human serology, and experimental animal models which support the viral model of schizophrenia.

[Seasonality of Schizophrenia: Findings of a Descriptive Study in Santa Marta, Colombia]

Introduction

Multiple studies carried out around the globe have concluded that there is a seasonal effect on the births of patients that will go on to develop schizophrenia later on. A relationship between being exposed to certain infectious agents during the prenatal period and possible direct effects on the developing brain that will later be expressed by the classical clinical picture has been suggested.

Objective

To analyze the behavior of births in a sample of individuals with schizophrenia from Santa Marta, Colombia.

Methods

Descriptive study based on the review of clinical histories of the patients seen in a psychiatric institute.

Discussion

A larger number of births took place during the rainiest months of the year suggesting a possible seasonal effect. However, the lack of data on births in Santa Marta during the years of the study did not allow a comparison between the results of the study and the birth rates of the general population. Even so, these findings have implications for future research regarding seasonality of schizophrenia in Colombia. They do not reflect an individual risk of developing the illness but they do document the characteristics of the temporal behavior of the births in the sample studied. Further studies that overcome the limitations of the present one are needed.

Correlation between schizophrenia and seasonality of birth in a tropical region

OBJECTIVE: To investigate the statistical relationship between season of birth and schizophrenia in 461 patients hospitalized in three psychiatric facilities in the towns of Araras, Itapira, and Espírito Santo do Pinhal, interior of São Paulo State, southeastern Brazil. METHODS: Date and place of birth of the patients were collected and used to determine the season of birth. Results were analyzed by the chi-square test. Data regarding temperature and rainfall between 1952 and 1986, corresponding to the years of birth of the patients studied, were also obtained. RESULTS: The results showed a higher prevalence of births in the winter months (p = 0.0044), a period characterized in this region by a decline in temperature and rainfall. CONCLUSION: These findings indicate a possible influence of seasonality on the pathogenesis of schizophrenia and suggest that the winter in this region, together with other factors, may contribute to the late development of the disease.

Excess in the spring and deficit in the autumn in birth rates of male schizophrenic patients in Italy: potential role of perinatal risk factors

OBJECTIVE

The aim of this study was to evaluate whether there were different seasonal variations of births in an Italian population of patients with schizophrenia, with other psychotic disorders, and with personality disorders than in the general population.

METHODS

Birth dates of 1270 patients admitted to one university psychiatric unit in Rome between 1990 and 2003, with a diagnosis of schizophrenia, other psychotic disorder (OPD) and personality disorder/cluster A (PD) were analyzed according to seasonal variation.

RESULTS

A significant excess of births in spring (with a peak in May) and a deficit in autumn (with a trough in October) was found in the sample of male schizophrenics (n = 506). No statistically significant variations were found in either the sample of female schizophrenics (n = 88) or in the combined sample with OPD and PD (n = 676).

CONCLUSIONS

The findings serve to strengthen the existing hypotheses that schizophrenia is related to environmental factors acting on the development of the central nervous system intrauterinely.

Explaining variation in the premorbid adjustment of schizophrenia patients: the role of season of birth and family history

Several studies have shown that patients with schizophrenia are more likely to be born in the winter and early spring than at any other time of the year. Furthermore, some studies have reported that winter-born patients differ from non-winter-born patients in terms of risk factors, symptoms, sensory abnormalities and brain morphology. Associations between season of birth and premorbid adjustment (PMA), however, are still unclear.

OBJECTIVE

The main purpose of this study was to determine whether winter-born and non-winter-born schizophrenia patients differ in terms of PMA and to examine how family history of schizophrenia-spectrum disorders may influence the association.

METHOD

Data on four PMA dimensions (attention, internalizing, externalizing and social problems) and family history were gathered from 37 schizophrenia patients (26 males and 11 females) and their mothers.

RESULTS

Non-winter-birth and a positive family history of schizophrenia-spectrum disorders were associated with worse PMA. Results suggest that, although no significant interaction was found, season of birth and family history appear to work together in explaining distinct dimensions of PMA.

What causes seasonality of birth in schizophrenia?

An excess of winter-spring births (and/or a decrease of summer births) has consistently been observed in schizophrenia (SCZ). This observation may provide a significant clue about the causes of the disease if specific factors which cause the phenomenon can be determined. This paper reviews several studies which investigated factors correlated with this observation in SCZ, in an attempt to determine which factors more likely cause the seasonality. Among the candidates of the factors are meteorological variables (such as ambient temperature), several infections, maternal hormones, sperm quality, nutrition and external toxins. A variation of procreation might also have an effect. Among the factors, the most extensively studied are temperature and viral infections. Some of them have appeared promising, but further studies are definitely required. Several challenges, including complicated correlations of the factors and determination of the susceptible period during pregnancy, need to be overcome. Comparisons of the data from areas and cohorts with different patterns of the candidate factors may be helpful. Animal studies may also help investigate the molecular and physiological mechanisms of the phenomenon.

No association between season of birth of patients with schizophrenia and risk of schizophrenia among their siblings

Previous studies on the relationship between the season of birth of patients with schizophrenia and the risk of schizophrenia among their siblings have yielded contradictory results. We investigated whether proband's month of birth affects siblings' risk of developing schizophrenia. We used the Finnish Hospital Discharge Register to identify all patients born in Finland from 1950 to 1976 who had been hospitalized because of schizophrenia at least once between 1969 and 1995. Their siblings were identified from the National Population Register, and data on siblings were linked to the Hospital Discharge Register to obtain information on any hospitalizations. We used logistic regression to investigate a sibling's probability of developing schizophrenia, defining the proband initially as the first sibling in calendar time to develop schizophrenia, then as the affected sibling with lowest onset age. Within-family dependence was taken into account by using robust standard error estimates. Neither models found any association between proband's month of birth and siblings' odds of developing schizophrenia. Our results support those previous studies that found no association between proband's month of birth and family history of schizophrenia, and suggest that the winter-spring excess of births among patients with schizophrenia is not caused by any genetic or environmental risk factor that operates independently of other risk factors.

Schizophrenia and season of birth: relationship to geomagnetic storms

An excess pattern of winter and spring birth, of those later diagnosed as schizophrenic, has been clearly identified in most Northern Hemisphere samples with none or lesser variation in Equatorial or Southern Hemisphere samples. Pregnancy and birth complications, seasonal variations in light, weather, temperature, nutrition, toxins, body chemistry and gene expression have all been hypothesized as possible causes. In this study, the hypothesis was tested that seasonal variation in the geomagnetic field of the earth primarily as a result of geomagnetic storms (GMS) at crucial periods in intrauterine brain development, during months 2 to 7 of gestation could affect the later rate of development of schizophrenia. The biological plausibility of this hypothesis is also briefly reviewed. A sample of eight representative published studies of schizophrenic monthly birth variation were compared with averaged geomagnetic disturbance using two global indices (AA*) and (aa). Three samples showed a significant negative correlation to both geomagnetic indices, a further three a significant negative correlation to one of the geomagnetic indices, one showed no significant correlation to either index and one showed a significant positive correlation to one index. It is suggested that these findings are all consistent with the hypothesis and that geomagnetic disturbance or factors associated with this disturbance should be further investigated in birth seasonality studies.

Schizophrenia and season of birth in a tropical region: relationship to rainfall

Winter birth has been shown to increase the risk of schizophrenia in adult life. It has been hypothesized that this effect is due to seasonal variation in infectious diseases, including influenza, as exposure to influenza during mid gestation also increases the risk of schizophrenia. However, in many areas there is little variation in temperature during the year, although rainfall may vary greatly. We tested the hypothesis that, in a tropical region with wet and dry seasons, schizophrenia births would be related to rainfall. The data came from the city of Mossoro in north-eastern Brazil. In this area there is no meaningful variation in temperature, but there is a rainy season with little precipitation during the rest of the year. In this region, the prevalence of influenza parallels that of rainfall. There was a significant relationship between rainfall and the number of schizophrenia births three months later. In contrast, there was no significant relationship between rainfall and general population births three months later. The relationship of birth to rainfall, rather than winter birth, may be associated with risk of schizophrenia in tropical regions; exposure to influenza during gestation may be the basis for such a relationship.

Winter birth and biological family history in adopted schizophrenics

To investigate relationships between birth season and biological family history in schizophrenia, this study used a sample of schizophrenics that had the advantages of (a) particularly thorough diagnostic assessments of schizophrenics' relatives, including information from direct interviews as well as chart reviews, and (b) schizophrenic probands who were adopted at early age, mitigating the usual confounding of genetic and postnatal environmental influences of the family. Adopted schizophrenics with no biological family history of schizophrenia-spectrum disorders were significantly more likely to be born in winter months than were either (a) their own biological relatives, including their sibs and half-sibs, (b) schizophrenics with a positive family history for schizophrenia-spectrum disorders, or (c) people in the general population. Family-history-positive schizophrenics and their schizophrenic relatives were, in turn, significantly less likely than their own non-schizophrenic biological relatives to be born in the winter; schizophrenics in these families tended to be born in the milder-weather seasons, particularly the spring and fall. Results suggest that environmental factors associated with winter birth may be etiologically important in schizophrenia, particularly for cases in which familial liability factors are weak. By contrast, a familial, probably genetic, liability factor may be especially important in schizophrenics born in mild weather.

Season of birth and schizophrenia: a systematic review and meta-analysis of data from the Southern Hemisphere

AIMS

Data from the Northern Hemisphere support an excess of winter-spring births of individuals who later develop schizophrenia when compared with the general population. The data from the Southern Hemisphere have been less consistent. This paper will present a systematic review and meta-analysis of relevant data from the Southern Hemisphere.

METHODS

To identify relevant studies we searched electronic databases, reviewed citations from target publications and wrote letters to published authors in the field. The counts for observed and expected births were assessed in four planned comparisons. In the absence of significant heterogeneity, the data were combined using Mantel-Haenzel odds ratio in a fixed effect model.

RESULTS

Twelve studies were identified. Published and unpublished data from eight of these were able to be included in the analyses. For the two seasonal comparisons (n = 20,017), small but non-significant excesses were found in the first comparison (winter versus other seasons; OR = 1.04, 0.99-1.08) and for the second comparison (winter and spring versus other seasons; OR = 1.03, 0.99-1.07). For the two quarterly comparisons (n = 14,799), there was a small but non-significant excess found in the third comparison (third quarter versus other quarters; OR = 1.03, 0.98-1.09), and a small but non-significant deficit in the fourth comparison (third and fourth quarter versus other quarters OR = 0.99, 0.95-1.04).

CONCLUSIONS

Assuming that season of birth acts as a proxy marker for fluctuating non-genetic risk-modifying factors for schizophrenia, this review suggests that in the Southern Hemisphere these factors may be weaker, less prevalent, less regular, and/or may be modified by other confounding or modifying variables.

Seasonality of births in schizophrenia and bipolar disorder: a review of the literature

More than 250 studies, covering 29 Northern and five Southern Hemisphere countries, have been published on the birth seasonality of individuals who develop schizophrenia and/or bipolar disorder. Despite methodological problems, the studies are remarkably consistent in showing a 5-8% winter-spring excess of births for both schizophrenia and mania/bipolar disorder. This seasonal birth excess is also found in schizoaffective disorder (December-March), major depression (March-May), and autism (March) but not in other psychiatric conditions with the possible exceptions of eating disorders and antisocial personality disorder. The seasonal birth pattern also may shift over time. Attempts to correlate the seasonal birth excess with specific features of schizophrenia suggest that winter-spring births are probably related to urban births and to a negative family history. Possible correlations include lesser severity of illness and neurophysiological measures. There appears to be no correlation with gender, social class, race, measurable pregnancy and birth complications, clinical subtypes, or neurological, neuropsychological, or neuroimaging measures. Virtually no correlation studies have been done for bipolar disorder. Regarding the cause of the birth seasonality, statistical artifact and parental procreational habits are unlikely explanations. Seasonal effects of genes, subtle pregnancy and birth complications, light and internal chemistry, toxins, nutrition, temperature/weather, and infectious agents or a combination of these are all viable possibilities.