Bad fitness? Birth weight can be an indication

Long-term consequences of low weight at birth

Can you easily get out of breath? It may be because you were too small at birth. This is shown in a recent study that uncovered a link between low birth weight and an increased risk of poor fitness in adulthood.

Researchers at the Karolinska Institutet in Sweden found that people who were light in birth had poorer physical condition later in life than peers with normal birth weight. The results were recently published in the specialist journal “JAHA”.

Condition deteriorated in the Swedish population

Cardiorespiratory fitness describes the ability of the body to supply the muscles with oxygen during continued physical activity. This ability is important to stay healthy and to reduce the risk of numerous illnesses and premature death. A Swedish study showed that the proportion of Swedish adults and adolescents who are in poor condition almost doubled between 1995 and 2017. 46 percent of the population had poor cardiorespiratory fitness.

Looking for answers

Given the impact on public health, interest in researching the causes of poor cardiorespiratory fitness has increased. The researchers at the Karolinska Institutet therefore wanted to find out the causes of the generally deteriorating condition in the population.

The research team examined conditions such as lack of exercise as well as genetic factors. It was shown that premature birth and the associated low birth weight are associated with low cardiorespiratory fitness in later life.

From birth to conscription

To analyze this aspect more closely, the researchers tracked the data from 280,000 men. With the help of the Swedish Population Register, they were able to determine their birth weight and the team received data on physical fitness through the compulsory military placement test, which the men aged between 17 and 24 completed. This context showed that men with low birth weight performed worse on average in the fitness test than men with normal birth weight. For every 450 grams of extra weight at birth, the performance on the ergometer increases by an average of 7.9 watts.

Alarming difference

"The extent of the difference we observed is alarming," emphasizes Daniel Berglind from the research team. “The observed increase of 7.9 watts per 450 grams of additional weight at birth corresponds to an increase in the metabolic equivalent (MET) of approximately 1.34, with a difference of 13 percent in the risk of premature death and 15 percent in the risk of the development of cardiovascular diseases is related. "

Great importance for public health

The researchers are convinced that the results are of great importance for public health, since around 15 percent of babies born worldwide weigh less than 2.5 kg at birth. Such birth weights can have important health effects in adulthood.

"Proper prenatal care can be an effective way to improve adult health, not only by preventing proven low birth weight damage, but also by improving cardiorespiratory fitness," added Viktor H. Ahlqvist, one of the study authors. The results underline the importance of prevention strategies to prevent low birth weights. (vb)

Author and source information

This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.

Graduate editor (FH) Volker Blasek


  • Viktor H. Ahlqvist, Margareta Persson, Francisco B. Ortega, et al .: Birth Weight and Cardiorespiratory Fitness Among Young Men Born at Term: The Role of Genetic and Environmental Factors; in: JAHA, 2020,
  • Karolinska Institutet: Get easily out of breath? It may be because you were small at birth, study finds (published: 31.01.2020),

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