Cardiovascular disease in people born to unmarried mothers in two historical periods: The Helsinki Birth Cohort Study 1934-1944

Aims: Socio-economic conditions in early life are important contributors to cardiovascular disease - the leading cause of mortality globally - in later life. We studied coronary heart disease (CHD) and stroke in adulthood among people born out of wedlock in two historical periods: before and during World War II in Finland. Methods: We compared offspring born out of wedlock before (1934 1939) and during (1940 1944) World War II with the offspring of married mothers in the Helsinki Birth Cohort Study. The war affected the position of unmarried mothers in society. We followed the study subjects from 1971 to 2014 and identified deaths and hospital admissions from CIID and stroke. Data were analysed using a Cox regression, adjusting for other childhood and adulthood socio-economic circumstances. Results: The rate of out-of-wedlock births was 240/4052 (5.9%) before World War II and 397/9197 (4.3%) during World War II. Among those born before World War II, out-of-wedlock birth was associated with an increased risk of stroke (hazard ratio (HR)=1.44; 95% confidence interval (CI) 1.00-2.07) and CHD (HR=1.37; 95% CI 1.02-1.86). Among those born out of wedlock during World War II, the risks of stroke (HR=0.89; 95% CI 0.58-1.36) and CHD (HR=0.70; 95% CI 0.48=1.03) were similar to those observed for the offspring of married mothers. The p-values for interaction of unmarriedxWorld War II were (p=0.015) for stroke and (p=0.003) for CHD. Conclusions: In a society in which marriage is normative, being born out of wedlock is an important predictor of lifelong health disadvantage. However, this may change rapidly when societal circumstances change, such as during a war.