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.