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The authors investigated the shape, sex- and age-dependency, and possible confounding of the association between birth weight and systolic blood pressure (SBP) in 197,954 adults from 20 Nordic cohorts (birth years 1910-1987), one of which included 166,249 Swedish male conscripts. Random-effects meta-regression analyses were performed on estimates obtained from age- and sex-stratified analyses within each of the cohorts. There was an inverse association between birth weight and SBP, irrespective of adjustment for concurrent body mass index. The association was linear for males, but for females with a birth weight greater than 4 kg, SBP increased with birth weight (p < 0.01). The association was stronger in the older age groups (p < 0.05), although this could have been a birth cohort effect. The association was stronger among females than among males (p = 0.005) when birth weight was less than or equal to 4 kg. The estimated effect of birth weight on SBP at age 50 years was -1.52 mmHg/kg (95% confidence interval: -2.27, -0.77) in men and -2.80 mmHg/kg (95% confidence interval: -3.85, -1.76) in women. Exclusion of the Swedish conscripts produced nearly identical results. This meta-analysis supports the evidence of an inverse birth weight-SBP association, regardless of adjustment for concurrent body size. It also reveals important heterogeneity in the shape and strength of the association by sex and age.

Because high body iron stores have been suggested as a risk factor for acute myocardial infarction, donation of blood could theoretically reduce the risk by lowering body iron stores. For this reason, the authors tested the hypothesis that voluntary blood donation is associated with reduced risk of acute myocardial infarction in a prospective epidemiologic follow-up study in men from eastern Finland. The subjects are all participants of the Kuopio Ischaemic Heart Disease Risk Factor Study. A cohort of 2,862 men aged 42-60 years were followed for an average of almost 9 years. One man (0.7%) out of 153 men who had donated blood in 24 months preceding the baseline examination experienced an acute myocardial infarction during 1984 to 1995, whereas 316 men (12.5%) of 2,529 non-blood donors had an acute myocardial infarction (p < 0.0001 for difference between proportions). In a Cox proportional hazards model adjusting for age, examination years and all other predictive coronary disease risk factors, blood donors had a 88% reduced risk (relative hazard = 0.12, 95% confidence interval 0.02-0.86, p = 0.035) of acute myocardial infarction, compared with non-blood donors. These findings suggest that frequent blood loss through voluntary blood donations may be associated with a reduced risk of acute myocardial infarction in middle-aged men.