A new study published in Nature Communications has found that protein levels in human blood change significantly during childhood and adolescence — and that these shifts are far more pronounced than previously thought.

Researchers from the Karolinska Institute, together with colleagues from SciLifeLab and the Royal Institute of Technology in Sweden, analyzed blood samples from 100 participants in the long-term BAMSE project, tracking them at ages 4, 8, 16, and 24. In total, they measured more than 5,000 proteins.

The results showed that more than half of these proteins undergo noticeable changes already in childhood. The most dramatic shifts occur during adolescence — roughly between the ages of 8 and 16, during puberty. At this stage, many proteins either increase or decrease sharply before stabilizing in adulthood.

The scientists also found that differences between boys and girls are minimal at first but become increasingly pronounced from adolescence onward. By the age of 24, around 30% of proteins differ between men and women. These differences are linked to growth, metabolism, the immune system, and reproductive processes.

The study’s key takeaway is that “normal” adult protein values cannot be applied to children and adolescents. As their bodies are in constant development, the same показатели can have entirely different meanings depending on age and sex.

This is particularly important because blood proteins are widely used as medical markers — for example, to detect inflammation, hormonal imbalances, or cardiovascular and metabolic diseases. The findings suggest that without age- and sex-specific reference ranges, such tests may provide a misleading picture in children.

The authors believe that creating a comprehensive “protein development map” will improve understanding of normal human development and, in the future, help detect abnormalities and disease risks at an earlier stage.