Is it the parents' fault?

Short mums and fat dads are making babies that grow
into adults with serious health problems

BY WILLIAM D DONALDSON

As a rule, heavier newborns turn into heavier adults. But epidemiologists are increasingly aware that many underweight newborns grow into adults at high risk of diseases such as diabetes and heart disease, which are normally associated with obesity. It's become obvious in recent years that overweight people who were born too light run health risks greater than might be expected from their adult weight.

A team of British epidemiologists set out to discover what these people have in common. They looked at the birth data and follow-up of over 11,000 men and women born in 1958 who took part in Britain's Perinatal Mortality Survey. Their findings, published in the Journal of Epidemiology and Community Health, reveal a subset of people who are apparently doomed from birth to suffer worse than average cardiovascular health. As might be expected in Britain, social class plays a key role in deciding who loses out in this birth lottery.

Four factors led to a significantly increased risk of being underweight at birth but overweight later in life. The least surprising of these was maternal smoking, already known to be associated with premature and underweight birth. Maternal smoking during pregnancy doubled the child's chances of falling into the high-risk group, defined as those who were in the lowest third of the population for birthweight but in the highest third for body mass index (BMI) at age 33. Low social class played a role nearly as significant, increasing by 55% the likelihood that a child would fall into the high-risk group.

Mothers who were shorter and fathers who were fatter were also more likely to produce offspring with low birth weight and high adult BMI. Professor Chris Power, of the Institute for Child Health in London, one of the study's authors, explains that children of heavier mothers are less likely to be underweight at birth, and therefore are less likely to be high-risk according to the study's definition. High paternal BMI, on the other hand, increases the child's risk of being an overweight adult without decreasing the risk of being an underweight baby, so it emerges as more statistically significant. Low maternal height is an indicator of poor lifetime nutrition, suggesting that the high-risk baby's problems begin before it is even conceived.

"Catch up growth in early life has been related to subsequent adiposity, but only to age five," says Professor Power. "Our study extends to a measure of obesity in adulthood." He says these children usually continue to gain weight faster than their peers for at least the first three decades of life. They are also generally shorter, even though they may catch up in height temporarily around puberty. In fact, they frequently experience puberty unusually young.