Relation between number of siblings and adult mortality and stroke risk: 25 year follow up of men in the Collaborative study

Abstract

Study objective: To investigate the relation between number of siblings, mortality risk, and stroke risk. Design: Prospective cohort study. Setting: 27 workplaces in Scotland. Participants: 5765 employed men aged 35-64 from a variety of different workplaces, screened between 1970 and 1973. Main results: There were strong relationships between number of siblings and socioeconomic variables and also with adult behavioural measures. Men with greater numbers of siblings had an increased risk of dying of all causes, coronary heart disease, lung cancer, stomach cancer, and respiratory disease over a 25 year follow up period. Adjustment for risk factors could explain these associations, excepting stomach cancer mortality. With the definition of stroke as either a hospital admission for stroke or death from stroke, there was a strong relation between number of siblings and haemorrhagic stroke, but not ischaemic stroke. Conclusions: Number of siblings is strongly related to mortality risk, but as it is also related to many risk factors, adjustment for these can generally explain the relation with mortality. The exceptions are stomach cancer mortality and haemorrhagic stroke, which are known to be related to deprivation in childhood, and, in the case of stomach cancer to childhood infection.

Association between number of siblings and cause-specific mortality in the Glasgow alumni cohort study

“…Furthermore, this weak increase in risk was not confirmed for CHD or stroke mortality. Hart et al reported a higher risk of haemorrhagic stroke with greater number of siblings [7] but in the current study there were insufficient confirmed deaths from haemorrhagic and ischemic stroke to assess these outcomes separately. We did not find a previously reported higher mortality due to stomach cancer [7], which is thought to indicate a higher risk of infection by Helicobacter Pylori in childhood.…”

“…Hart et al reported a higher risk of haemorrhagic stroke with greater number of siblings [7] but in the current study there were insufficient confirmed deaths from haemorrhagic and ischemic stroke to assess these outcomes separately. We did not find a previously reported higher mortality due to stomach cancer [7], which is thought to indicate a higher risk of infection by Helicobacter Pylori in childhood. Increasing sibling number can lead to a higher transmission rate of an infectious agent, but this may actually occur only in the presence of other risk factors, such as overcrowding.…”

“…Although potentially pointing to exposures and mechanisms linking early life factors and adult health this association has not been systematically investigated in epidemiological studies. For example, more siblings might correlate with more infections during childhood, an exposure which has been positively associated with higher stomach cancer mortality [7] and lower risk of allergy-related diseases [8]. However, greater number of siblings is strongly correlated, in most contemporary industrialized societies, with poor socioeconomic circumstances, which are associated with higher mortality for some causes of death, such as stomach cancer and haemorrhagic stroke and, less strongly, coronary heart disease [9,10].…”

“…In a Swedish study, having four or more siblings was positively related to poorer health in adulthood, and although there were no differences in mortality risk, only 3 years of mortality follow-up were available [6]. A study in Scotland, with longer follow-up, found that number of siblings was positively related to adult mortality risk for some specific causes of death [7]. Although potentially pointing to exposures and mechanisms linking early life factors and adult health this association has not been systematically investigated in epidemiological studies.…”

“…Number of siblings has been traditionally used as a proxy for two exposures, poor early life socioeconomic circumstances (in industrialized societies) and exposure to early life infections (e.g. for stomach cancer [7] and allergic diseases [13]). These are the main pathways that are hypothesized in this manuscript.…”