Birth weight, childhood body mass index and risk of coronary heart disease in adults: combined historical cohort studies

Abstract

Background: Low birth weight and high childhood body mass index (BMI) is each associated with an increased risk of coronary heart disease (CHD) in adult life. We studied individual and combined associations of birth weight and childhood BMI with the risk of CHD in adulthood.

Methods/principal findings: Birth weight and BMI at age seven years were available in 216,771 Danish and Finnish individuals born 1924-1976. Linkage to national registers for hospitalization and causes of death identified 8,805 CHD events during up to 33 years of follow-up (median = 24 years) after age 25 years. Analyses were conducted with Cox regression based on restricted cubic splines. Using median birth weight of 3.4 kg as reference, a non-linear relation between birth weight and CHD was found. It was not significantly different between cohorts, or between men and women, nor was the association altered by childhood BMI. For birth weights below 3.4 kg, the risk of CHD increased linearly and reached 1.28 (95% confidence limits: 1.13 to 1.44) at 2 kg. Above 3.4 kg the association weakened, and from about 4 kg there was virtually no association. BMI at age seven years was strongly positively associated with the risk of CHD and the relation was not altered by birth weight. The excess risk in individuals with a birth weight of 2.5 kg and a BMI of 17.7 kg/m(2) at age seven years was 44% (95% CI: 30% to 59%) compared with individuals with median values of birth weight (3.4 kg) and BMI (15.3 kg/m(2)).

Conclusions/significance: Birth weight and BMI at age seven years appeared independently associated with the risk of CHD in adulthood. From a public health perspective we suggest that particular attention should be paid to children with a birth weight below the average in combination with excess relative weight in childhood.

Figure 1. Risk of coronary heart disease in adulthood according to birth weight.

The estimates are adjusted for sex and cohort (Danish or Finnish), estimated by Cox regression based on restricted cubic splines with age as the underlying time scale. The dashed line shows the estimates without adjustment for BMI at age seven years, the bold line shows the estimates with adjustment for BMI at age seven years and the dotted lines show the 95% confidence limits for the adjusted estimates.

Figure 2. Risk of coronary heart disease in adulthood according to BMI at age seven years.

The estimates are adjusted for sex and cohort (Danish or Finnish), estimated by Cox regression based on restricted cubic splines with age as the underlying time scale and truncated to depict the inner 98% of the BMI distribution. The dashed line shows the estimates without adjustment for birth weight, the bold line shows the estimates with adjustment for birth weight and the dotted lines show the 95% confidence limits for the adjusted estimates.

Figure 3. Risk of coronary heart disease according to birth weight and BMI at age seven years.

The estimates are adjusted for sex and cohort (Danish or Finnish), estimated by Cox regression with age as the underlying time scale. The lines join points with the same hazard ratio for CHD and are truncated to depict the inner 98% of the BMI distribution. Arrows indicate median values, the plus indicates the risk at the joint median and the M indicates the minimum risk.