Obesity and diabetes have become globally epidemic. The cause of this unprecedented rise in obesity is multifactorial, with inactivity, excessive calorie intake, and genetic factors implicated. More recent data indicate that exposure to diabetes during pregnancy increases the risk of childhood and adult obesity, diabetes, and cardiovascular disease. Evidence derived from recent randomized controlled trials indicates that gestational diabetes mellitus (GDM) treatment reduces newborn obesity and therefore may contribute to reducing the global prevalence of obesity and metabolic syndrome. Current evidence detailing increases in global prevalence of obesity was reviewed together with data evaluating the effectiveness of treatment of GDM. Development of new protocols for diagnosis and treatment of GDM may reduce population obesity and cardiovascular disease.
The metabolic syndrome, also called the insulin resistance syndrome, was characterized by Reaven in a 1988 Banting lecture as a combination of glucose intolerance, hyperinsulinemia, hyperlipidemia, central obesity, and hypertension. These abnormalities predispose to a significant increase of morbidity and mortality from cardiovascular disease and type 2 diabetes mellitus. The metabolic syndrome has now become epidemic in both developed and developing countries.
There is now strong and convincing evidence linking childhood obesity and adult metabolic syndrome and, more recently, linking adult insulin resistance states to utero fetal adiposity. The development of in utero fetal adiposity, which arises in response to maternal hyperglycemia during pregnancy, is correlated with the subsequent development of childhood and adult obesity and even diabetes. Thus, when addressing the controversy of treatment or nontreatment of gestational diabetes mellitus (GDM), it is essential to consider not only fetal and neonatal outcomes but also the downstream effects on childhood and adult health.
Obesity: today’s global imperative
Since obesity is the single most powerful risk factor for pregnant women developing GDM, understanding the current state of worldwide obesity provides a useful context in which to evaluate the implications of protocols for treatment of GDM. There has been a marked (≥40%) increase in the overweight rate and in obesity in the last decade, and, while this increase has occurred most markedly in the United States, this is now clearly a global phenomenon, with very few countries unaffected.
Currently >1 billion adults are overweight and at least 400 million are clinically obese. Even in relatively low-prevalence countries, such as China, rates are almost 20% in urban areas. The World Health Organization projects that by 2015, approximately 2.3 billion adults will be overweight and >700 million will be obese, representing near doubling of obesity in a decade. In a growing number of countries, the health threat associated with obesity now far exceeds the former nemesis of starvation and undernutrition.
Obesity plagues not only adults. Childhood obesity is already epidemic in many areas and on the rise in others, with 17.6 million children estimated to be overweight worldwide. The childhood obesity problem increasingly extends into the developing world: the obesity prevalence among 5- to 12-year-olds in Thailand increased from 12–15% in just 2 years. Obesity accounts for 2–6% of total health care costs in several developed countries, with the true costs much greater, as not all obesity-related conditions are included in the calculations.
The epicenter of the childhood obesity epidemic has clearly been in the United States, with the US Surgeon General estimating that since 1980 the number of overweight children has doubled and the number of overweight adolescents has tripled. Obesity prevalence among youths has also increased dramatically, from approximately 5% in the 1970s to >15% in the National Health and Nutrition Examination Survey (NHANES) survey of 1999–2002 ( Figure 1 ). Children of non-white minorities (African American and Hispanic) are particularly affected, with obesity rates 40–90% above the values experienced by whites.
The global increase in childhood obesity not only presages an epidemic of adult cardiovascular and orthopedic disease, but because obesity is a precursor of type 2 diabetes mellitus, which in turn accelerates the cardiovascular complications of obesity, an avalanche of diabetes is undoubtedly underway as well.
Rising obesity leads to increased diabetes prevalence
While the picture of rising obesity rates is just now becoming clear, the data regarding the increasing prevalence of diabetes are much more robust. A recent report estimated worldwide diabetes prevalence by extrapolating data from a limited number of countries to 191 World Health Organization member states ( Figure 2 ). The prevalence of diabetes for all age groups worldwide was 2.8% in 2000 but estimated to increase by 57% by 2030, with the global number of people with diabetes projected to reach 366 million in 2030. Importantly, in the same 30-year period the number of women of reproductive age is expected to double.
In the United States, data reported in 2007 by the National Institute of Diabetes and Digestive and Kidney Diseases ( Figure 3 ) demonstrated a marked upswing in new cases of type 2 diabetes mellitus in children aged 10–19 years. Ethnicities disproportionately affected were those of Hispanic, African American, Pacific Islander, and American Indian ancestry. With regard to the prevalence of GDM in the United States, Dabelea et al documented a 30% increase in GDM prevalence (8–11%) among subscribers to a Colorado health maintenance organization in the decade from 1991–2008.
Unfortunately, this now-global avalanche of GDM and type 2 diabetes mellitus in both adults and children will, unless aggressively managed, lead to an avalanche of anomalous and obese newborns. As those newborns reach reproductive age and later adulthood, the public health and economic implications will be considerable in decades to come.
GDM: a cause of the metabolic syndrome?
Is it possible that exposure to hyperglycemia during fetal life, which accelerates fetal fat accretion and pancreatic hypertrophy, could have effects that extend into adulthood? The effects of in-utero exposure to GDM were described in a study of offspring of pregnancies in highly insulin-resistant Pima Indians. In this investigation, a cohort of siblings was identified, 1 of whom was born after a pregnancy complicated by diabetes, and another, older sibling, whose pregnancy was not complicated by diabetes. The siblings exposed to diabetes in utero and those not exposed came from similar gene pools and ate at the same table during their childhood years. However, the body mass index in the siblings exposed to diabetes in utero was twice that observed among the unexposed siblings by age 21 years ( Figure 4 ). In another Pima Indian study, women who were obese at birth, as indicated by ( Figure 3 ) a birthweight >4500 g, were at a 4-fold increased risk of developing GDM in their own pregnancies as adults.
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