Low weight at birth linked to poor physical fitness later in life: Study

Babies with low weight at birth may grow up to have bodies with weaker ability to supply oxygen to the muscles, according to a study which emphasises the importance of strategies to reduce low birth weight in infants.

According to researchers, including those from Karolinska Institute in Sweden, having a good cardiorespiratory fitness is important for staying healthy, and can reduce the risk of numerous diseases and premature death.

However, they said this ability of the body to supply oxygen to muscles during exercise is declining globally, both for youths and adults.

The current study, published in the Journal of the American Heart Association, assessed if low birth weights played a role for cardiorespiratory fitness in individuals born after pregnancy of 37-41 weeks.

In the study, the scientists followed more than 2,80,000 males from birth to military conscription at age 17-24 using Swedish population-based registers.

They found that those born with higher birth weights performed significantly better in a fitness test on a cycle ergometer -- a stationary bicycle equipped with an instrument to measure the amount of work done by the individual peddling the bike.

According to the study, for every 450 grams of extra weight at birth, in a baby born at 40 weeks, the maximum work capacity on the bicycle increased by an average of 7.9 watts.

The scientists added that the association was stable across all categories of weights of individuals in young adulthood, and was largely similar in a subset analysis of more than 52,000 siblings.

Based on these findings, the researchers said current weight and shared genetic and environmental factors alone cannot explain the link between birth weight and cardiorespiratory fitness.

"The observed 7.9 watts increase for each 450 grams of extra weight at birth, in a baby born at 40 weeks, translates into approximately 1.34 increase in metabolic equivalent (MET) which has been associated with a 13 per cent difference in the risk of premature death, and a 15 per cent difference in the risk of developing cardiovascular disease," said Daniel Berglind, study co-author from Karolinska Institutet.

"Such differences in mortality are similar to the effect of a 7-centimeter reduction in waist circumference," Berglind added.

According to the researchers, the findings are of significance to public health, since about 15 per cent of babies born globally weigh less than 2.5 kilogrammes at birth.

"Providing adequate prenatal care may be an effective means of improving adult health not only through prevention of established harms associated with low birth weight but also via improved cardiorespiratory fitness," said study co-author Viktor H. Ahlqvist from Karolinska Institute.