High birth weight does not guarantee protection from type 2 diabetes

¹ Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, Alberta T6G 2P5, Canada, E-mail: noreen.willows{at}ualberta.ca
² School of Dietetics and Human Nutrition, McGill University, Montreal, Quebec, Canada

Dear Sir:

The August 2002 issue of the Journal featured an article by Birgisdottir et al (1) suggesting that infants with high birth weights and lengths are protected from glucose intolerance as adults. The Icelandic population that was the focus of the study is genetically homogeneous and has higher birth weights and a lower prevalence of type 2 diabetes than do neighboring countries. The seemingly protective effect of large body size against dysglycemia that was observed in Iceland may not exist in other genetically homogeneous populations in whom birth weight is also high, such as Native North American Indians. As in Iceland, aboriginal women in Canada—many of whom are overweight—give birth to infants with exceptionally high weights and lengths (2–5). In contrast with the prevalence in Iceland, the prevalence of type 2 diabetes and gestational diabetes in Canada is high among aboriginal peoples (4–6). Currently, there is a high prevalence of both high infant birth weight and type 2 diabetes in aboriginal communities. This observation contrasts that of 40 y ago, when—at the population level—there was a low prevalence of type 2 diabetes, and many aboriginal infants had low birth weight (6). Birgisdottir et al recommend decreasing the prevalence of low-birth-weight infants as a strategy to lower the worldwide prevalence of type 2 diabetes. A decrease in the prevalence of low birth weight is a laudable goal; however, given the positive association at the population level between infant birth weight and abnormalities in glucose tolerance observed in Canadian aboriginal populations, it is not clear that the ensuing outcome of decreasing low birth weight would be a global reduction in the prevalence of type 2 diabetes.

The intrauterine glycemic environment may predispose the fetus to develop type 2 diabetes and, in aboriginal populations, many high-birth-weight infants are born to women with gestational diabetes or type 2 diabetes (4, 5). In Iceland, it may be precisely the low prevalence of type 2 diabetes and gestational diabetes in the population that accounts for the low prevalence of type 2 diabetes in the offspring born with high weights. As mentioned by the authors, other intervening factors may be responsible for the negative association between infant birth weight and type 2 diabetes in Iceland, such as protective dietary practices. For example, coastal populations such as those in Iceland, who have a diet high in fish, would be expected to give birth to infants with high birth weights and a lower prevalence of glucose intolerance because of the n-3 fatty acids found in fish (7, 8). The general tallness of Scandinavian populations must be considered as a confounding variable. A secular increase in infant birth weight in Iceland has been attributed to an increase in maternal height (9). Tall women are also likely to give birth to infants with high lengths; these long infants are often tall as adults (10). In general, adults with tall statures are less likely than are those with short statures to be predisposed to abnormal glucose tolerance, including the development of gestational diabetes, for reasons that are not clear (11). It may also be that a protective effect of very high infant birth weight against dysglycemia is unique to the Icelandic population for unknown reasons and that the results of the study cannot be extrapolated to other populations around the world.

REFERENCES

1. Birgisdottir BE, Gunnarsdottir I, Thorsdottir I, Gudnason V, Benediktsson R. Size at birth and glucose intolerance in a relatively genetically homogeneous, high–birth weight population. Am J Clin Nutr 2000;76:399–403.
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