Researchers have found that babies born with low birth weights are more likely to have poor cardiorespiratory fitness later in life than their normal-weight peers.

Having a good cardiorespiratory fitness is important for staying healthy and can reduce the risk of numerous diseases and premature death. Alarmingly, cardiorespiratory fitness is declining globally, both for youths and adults.

The study, published in the journal JAHA, showed that the proportion of Swedish adults with low cardiorespiratory fitness almost doubled from 27 per cent in 1995 to 46 per cent in 2017.

According to the researchers, the magnitude of the difference observed is alarming.

“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 study researcher Daniel Berglind from Karolinska Institutet in Sweden.

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

According to the study, researchers have identified both physical inactivity and genetic factors as important determinants.

Preterm delivery, and the low birth weight associated with it, has also been linked to low cardiorespiratory fitness later in life.

In this study, the researchers wanted to examine if low birth weights played a role for cardiorespiratory fitness in individuals born after pregnancy of 37-41 weeks.

They followed more than 280,000 males from birth to military conscription at age 17-24 using Swedish population-based registers.

At conscription, the men underwent a physical examination that included an evaluation of their maximal aerobic performance on a bicycle ergometer.

The researchers found that those born with higher birth weights performed significantly better on the cardiorespiratory fitness test.

The researchers believe the findings are of significance to public health, seeing as about 15 per cent of babies born globally weigh less than 2.5 kilos at birth and as cardiorespiratory fitness have important implications for adult health.