Central or "trunk" fat in young boys was associated with elevated BP in one study (Source: South Park Studios/Comedy Central)

One of the Circulation studies found that low-weight babies who put on more pounds than normal during childhood are more likely to have hypertension as young adults. A separate study found that central or "trunk" fat in young boys, regardless of race, was associated with elevated blood pressure (BP), although the association was not seen in girls. The Pediatrics paper found that infants who gained significant weight within the first 4 months of life were more likely to be overweight at age 7, regardless of their birth weight or weight at 1 year of age.

All of the researchers note that patterns of weight gain in childhood and adolescence affect the development of obesity, hypertension, and CVD later in life. "Children who have higher body mass are more likely to become obese as adults, a matter of public health concern in view of the marked rise in both the mean body mass and the prevalence of obesity in children," Dr Catherine M Law (University of Southampton, UK) and colleagues write. Less clear is whether different developmental stages are more important for different diseases.

In an interview with heartwire, Law pointed out that the theory that certain biologic or metabolic mechanisms responsible for regulating factors such as obesity or BP begin early in life is by no means novel. "There has been work on this hypothesis over the past 20 years; it's not new this week." By trying to hone in on things like weight gain at different stages of development, however, researchers can start to understand "where, why, for which particular diseases, and therefore when and how you can act on that information."

Law elaborates, "We're now getting detail around this common hypothesis that something early in life determines your risk of disease in your 60s and 70s. And the detail, we're guessing, really means that we're not really able to say that there's a single common thing that applies for obesity and hypertension and diabetes and coronary heart disease. There's probably going to be important but relatively subtle differences between them."

Law's hypothesis helps explain why studies looking at different, though related outcomes have sometimes appeared to have contradictory results. For instance, a longitudinal study of Finnish babies appearing in the spring of 2001 and reported by heartwire indicated that low-birth-weight babies who did not put on a lot of weight after 1 year were more likely to have coronary artery disease in adulthood.

"Hypertension and obesity aren't synonymous," says Law. "Most people with obesity actually have rather high blood pressure, but lots of hypertensives aren't obese . . . We tend to think of them as being very similar but there are actually very important differences and so therefore they may arise in some dissimilar ways."

Law et al studied 346 young adults age 21-24 in southern England who had had their weight measured at birth, during infancy, and at least once between age 1 and 6. They report that babies that had been underweight at birth, but had put on considerable weight during childhood had the highest BPs in adulthood, even after adjusting for adult body mass.

Of note, weight gain during infancy (up to 1 year) was not associated with adult systolic BP, but for every kilogram below normal in weight at birth, systolic BP was 2.7 mm Hg higher. Increased diastolic BP was also associated with low birth weight, but this relationship was not as strong as that seen with systolic BP.

The finding is important on several levels, the authors explain. "Reduced birth weight and rapid weight gain in childhood is becoming common in some populations, such as children growing up in developing countries where low birth weight is still prevalent." They also note that current pediatric practice is to promote "catch-up" growth in low-birth-weight babies.

"The worry has been, that when you have a low-birth-weight baby you're inclined to feed it to catch up from the insult it's had in utero, but doing that might lead to a higher risk of adult disease," says Law. "And why our negative finding with infant growth is important is that, at least with blood pressure, that doesn't seem to be the case."

Where rapid infant growth may be important is in setting in motion a process that contributes to childhood obesity. In their Pediatrics study of almost 20000 black and white children, Dr Nicolas Stettler (Children's Hospital, Philadelphia, PA) and colleagues found that the rate of weight gain during the first 4 months of life (at 100 g/month) was associated with being overweight at 7 years of age.

There are important differences between Stettler et al's paper, and that of Law et al's in Circulation. The latter was a prospective, cohort study that followed children from birth to age 7 looking specifically at the issue of overweight status. The former was a longitudinal study in which a previously studied patient cohort was re-evaluated more than 2 decades after the original measurements were taken. More importantly, Law et al were concerned primarily BP, not obesity, in relation to weight at birth, infancy, and childhood.

Something happens very early in life that sets various mechanisms or structures which then can't be altered. And they predict physiological and pathophysiological changes later in life.

Commenting on the Stettler et al's paper in relation to her own study, Law told heartwire, that there are "common features" to the papers. "What was being proposed both by our work and theirs is that something happens very early in life that sets various mechanisms or structures which then can't be altered. And they predict physiological and pathophysiological changes later in life."

Stettler and colleagues go one step further, stating that further research may lead to intervention strategies. "If this association is confirmed by other studies, the present results may lead to new approaches for the prevention of childhood obesity, aiming at an optimization of healthy nutrition and growth in infancy," the authors write.

When such a young and vulnerable population is involved, however, the concept of obesity prevention is a contentious one. Law, speaking to heartwire, called the idea of putting babies on diets "horrendous...and our paper is explicitly against that."

Stettler et al do not propose caloric restrictions for babies, but they do note that the American Academy of Pediatrics "emphasizes that exclusive breastfeeding is ideal nutrition and sufficient to support optimal growth and development in the first 6 months of life."

The second Circulation paper delves into other patterns of obesity, specifically body fat distribution and gender differences. In a cross-sectional analysis of children age 5-18 from 3 race groups (white, black, and Asian), Dr Qing He (Columbia University) and colleagues looked at BP relative to fat distribution. They were specifically interested in the link between excess trunk fat, that is, fat located in the central, "belly" area, and elevated BP. He et al measured fat using skin fold tests and dual energy X-ray absorptiometry (DMX) and adjusted to account for total body fat.

The researchers found a significant positive relationship between systolic and diastolic BP and trunk fat after adjusting for total fat in adolescent boys regardless of race. No such association was seen in girls.

"To really determine the clinical significance of what we've found you would need to follow these children longitudinally to see if the boys with higher trunk fat do indeed develop cardiovascular disease later in life," senior author Dympna Gallagher told heartwire. "However, based on the strength of the information that's already well known and established in adults, we know that adults with higher trunk fat have a higher incidence of cardiovascular disease. And that makes us believe that there may be merit in the assumption that children with a similar fat distribution might also be at increased risk."