Commentary: Maternal diet during pregnancy and blood pressure in the offspring

Abstract

Like other living creatures, human beings are plastic during development, they are able to adapt to the environment. There is now considerable evidence that coronary heart disease originates in developmental plasticity. Almost 100 studies assessing the link between birth weight and blood pressure have been performed worldwide. Two meta analyses have shown that low birth weight is consistently linked with an increased blood pressure in later life, 1 and that this association is similar for men and women. 2 Birth weight has been a central feature of epidemiological studies because it is a measurement that is readily available and has been recorded for many years. However, there is now evidence that fetal programming may occur in the absence of changes in fetal size. Recent research therefore has sought to identify the nature of the adverse maternal influences that raise blood pressure and alter levels of cardiovascular risk factors in the offspring. In this issue of the International Journal of Epidemiology, Huh et al. describe their study in which they assessed the direct impact of maternal diet during pregnancy on offspring’s blood pressure. 3 They studied the link between maternal protein intake in the first and second trimester and blood pressure of the offspring at the age of 6 months. Although they did confirm the well-described association between low birth weight and raised blood pressure, they could not detect an association between protein intake in the maternal diet during pregnancy and offspring’s blood pressure. The third trimester is thought to be a critical window for programming blood pressure. It is therefore a serious drawback of Huh’s study that the maternal diet was only studied in the first and second, but not third, trimester. Our study of men and women born around the time of the Dutch famine, for instance, has shown that blood pressure was linked to the balance between protein and carbohydrate intake in the maternal diet during the third, but not first and second trimester. 4 Similarly, a study in Aberdeen found that the blood pressures of men and women were related to the balance of carbohydrate and protein in their mother’s diet during late pregnancy. 5 At either extreme of this balance, their blood pressures were raised, even if their growth in utero was not affected. The influence of the maternal diet on offspring’s blood pressure is complex. Animal studies show that the effects of protein restriction in the diet of pregnant rats on the blood pressure of their offspring are stronger than the effects of caloric restriction with a balanced reduction of all macro-nutrients. 6 Moreover, the effects seem to depend not only on the composition of the diet with respect to macro-nutrients in general, but also with respect to the source of macro-nutrients in the diet. Giving low protein diets to pregnant rats raises blood pressure in the offspring if the diets contain fats rich in linoleic acid, 6 whereas no effects on blood pressure are found in similar experiments using a diet containing fats rich in linolenic acid. 7 Furthermore, the blood pressure raising effect of protein restriction can be prevented by supplementing the maternal diet with glycine. 8 Most studies relating maternal diet to offspring’s blood pressure show that blood pressure of the offspring may be programmed through the maternal diet without affecting the size of the baby at birth. 4,5 Evidence from animal studies leads to similar conclusions: the programming of adult physiology can occur as a result of maternal factors that either do not alter fetal growth or result in alterations in organ growth and body composition but have little or no effect on size at birth.