Editorial Comment—Prenatal Influences on Stroke Mortality in England and Wales
Genetic and environmental factors may interact in complex ways to alter an individual’s susceptibility to a variety of diseases, including stroke. Analysis of epidemiological data in the present study shows that people who were born in areas of high stroke mortality in England and Wales were at higher risk of stroke-related mortality than those migrating into these localities.1 The same may be true in the United States. South Carolina has one of the highest stroke mortality rates in the southeastern “stroke belt” region of the country,2 the existence of which is not fully understood.3 Those born and residing in South Carolina have higher stroke mortality rates than those who were born outside of the stroke belt and then moved to the state.4 Those residing in South Carolina who were born in other areas of the stroke belt have intermediate rates.
Why would place of birth affect stroke, a disease occurring decades later? The present study also finds that stroke mortality rates among adults in England and Wales are higher among persons who had lower birth weights. By analogy to their present results, the authors hypothesize that lower birth weights might at least partially underlie the US stroke belt as well. An abstract presented at the 2003 International Stroke Conference supports this view.5 This study compared a group of South Carolina Medicaid Beneficiaries having stroke under 50 years of age to population controls. The odds of stroke were more than double for those with birth weights <2500 g as compared with those weighing ≥4000 g (with a significant linear trend for intermediate birth weights). As in the present study, geographic variation in birth weight was further associated with geographic variation in deaths due to stroke.
Birth weight may be influenced by a variety of factors, including the mother’s socioeconomic status. However, present local socioeconomic conditions explain <16% of the geographic variation in excess stroke-related mortality in the United States.6 The areas of England and Wales with current high stroke mortality rates were characterized by poor living standards when present-day 60-, 70-, and 80-year-olds were born. However, this does not address whether the impact of poorer socioeconomic status is exerted during the prenatal period or during infancy. An additional important observation in the present study is that stroke mortality was not independently correlated with past postneonatal infant mortality, suggesting that prenatal or perinatal events initiate processes that lead to an increase risk of stroke decades later. On the basis on this and other work, the authors hypothesize that relatively poorer maternal nutrition during pregnancy may underlie their children’s relatively higher stroke-related mortality (and likely incidence) in later life.
Although Barker and Lackland provide a reasonable argument linking low birth weight with increases in stroke-related mortality in adults, they appropriately caution that their analyses reflect associations and not causality. Despite this inherent limitation of epidemiologically based observations, the data provide another compelling argument to ensure adequate prenatal care and maternal nutrition. Investment in programs aimed at optimizing maternal health and nutrition may pay dividends in reducing the incidence of stroke in their unborn babies when they reach adulthood. It is an investment in the future that may prove both effective and cost-effective.
Barker DJP, Lackland DT. Prenatal influences on stroke mortality in England and Wales. Stroke. 2003; 34: 1598–1603.
Casper ML, Barnett E, Williams GI, Halverson JA, Braham VE, and Greenlund KJ. Atlas of Stroke Mortality. Atlanta, Ga: Department of Health and Human Services, Centers for Disease Control and Prevention; 2003.
Lackland DT, Egan BM, Jones PJ. Impact of nativity and race on “stroke belt” mortality. Hypertension. 1999; 34: 57–62.
Lackland DT, Egan BM. The association of birth weight and stroke in the US stroke belt. Stroke. 2003; 34: 289.Abstract.
Howard G, Anderson R, Johnson NJ, Sorlie P, Russell G, Howard VJ. Evaluation of social status as a contributing factor to the stroke belt region of the United States. Stroke. 1997; 28: 936–940.