First born children are less likely to develop non-Hodgkin lymphoma

An Australian population based, case-control study shows that first born children are more likely to develop atopic conditions but less likely to develop non-Hodgkin lymphoma (NHL). This Australian case-control study was designed to investigate possible immune causes of NHL. It is known to be more common in people with immune suppression but its association with other immune states is unclear. Atopy is inversely associated with late birth order and childhood crowding. The fetus has a predominant Th2 response, which is necessary for the immunotolerance of pregnancy. The hygiene hypothesis suggests that exposure in very early life to pathogenic bacteria or their products, stimulates the switch to protective Th1-based immunity. If this exposure is delayed, a persistent Th2-dominant immune response can cause an increased incidence of atopic conditions.The NSW and ACT cancer registries were searched and 704 NHL patients aged 20 - 74 years without clinically apparent immune deficiency were identified. There were 694 control subjects, who were randomly selected from state electoral rolls and frequency-matched to case patients by age, sex, and area of residence. Birth order, childhood crowding, and history of atopic conditions (hay fever, asthma, eczema, and specific allergies) were assessed by questionnaire and interview. The study found that the odds ratios for developing NHL were 0.52 (95% CI, 0.32 to 0.84) for only children, 0.55 (95% CI, 0.40 to 0.75) for first-born children, 0.70 (95% CI, 0.51 to 0.96) for second-born children, and 0.81 (95% CI, 0.57 to 1.14) for third-born children (all compared with fourth- or later-born children) (p trend There was no association between indicators of crowding in later childhood, such as sharing a bed or bedroom, and NHL risk. A history of atopic conditions was associated with a reduced risk of NHL; this reduction was statistically significant for hay fever (OR, 0.65, 95% CI, 0.52 to 0.82) and food allergies (OR, 0.29, 95% CI, 0.20 to 0.42) with a trend for asthma and eczema (p = 0.09).The authors concluded that early birth order and its immunologic consequence, a Th2-dominated immune response, as reflected by a history of atopic disease, are associated with a reduced risk of NHL. Exposure to infection in early childhood is the important factor and later childhood conditions have less effect.Reference...