Study findings: Aging occurs in phases

Aging is often described as a slow process, where the body changes a little each year. Many people imagine that biological changes happen gradually and evenly throughout adulthood. But the study we take a closer look at here suggests that reality might be more complex.

By following healthy adults over several years and analysing thousands of biological markers in the body, the researchers found that aging at the molecular level does not unfold as a smooth, continuous process. Instead, the data show that there are specific periods in life when many biological changes occur at the same time.

Read along in this blog to find out what the study found.

About the study

The study Nonlinear dynamics of multi-omics profiles during human aging, published in Nature Aging in 2024, set out to examine how the body’s biological systems change across adulthood and whether these changes progress in a steady, linear way or occur more unevenly over time.

Instead of focusing on a single type of biological data, the researchers used a multi-omics approach, which is also reflected in the study’s title. This means that several biological layers were analysed at the same time, including molecular, metabolic, and protein-related data.

By combining these different “omics” levels, the researchers were able to observe how multiple systems in the body shift in parallel as people age, rather than viewing aging through one isolated biological lens.

Who participated in the study

The study included 108 healthy adults aged 25 to 75 years, all living in California, USA. All participants were free of known serious diseases at the time of enrolment.

Participants were followed for an average of 1.7 years, with some individuals followed for up to 6.8 years. During this period, biological samples were collected approximately every 3–6 months, resulting in a total of 5,405 analysed samples.

What did the researchers measure?

To examine how aging affects the body across multiple biological levels at the same time, the researchers used — as mentioned earlier — a multi-omics approach. The aim was to track biological changes over time within the same individuals and assess whether these changes occur gradually or in more uneven patterns across adulthood.

Here is what was measured:

• The microbiome, analysed from multiple body sites. This included stool samples to assess the gut microbiome, as well as skin, oral, and nasal swabs, reflecting the role of microorganisms in immune regulation and metabolic processes.

• Gene expression (transcriptomics) in specific immune cells from blood, showing which genes are active. These cells play a central role in immune function, and changes in gene activity can reflect shifts in metabolism and cellular stress responses linked to aging.

• Proteins, metabolites, and lipids in plasma, providing insight into biological function at the molecular level, including energy metabolism, cellular signalling, and metabolic regulation.

• Cytokines, which are small signalling proteins involved in immune regulation and inflammation. As chronic, low-grade inflammation is commonly associated with aging, cytokine profiles offer insight into age-related changes in immune activity.

• Clinical laboratory blood markers, included to link molecular-level changes with established indicators of physiological function and health status.

The results

With repeated measurements collected over several years, the researchers were able to examine how biological aging unfolds in practice. Analysis of the collected data revealed clear patterns in when biological changes occur across adulthood.

Non-linear patterns dominate

The analyses showed that only a small proportion of biological profiles changed linearly with age. For the majority of the measured molecular, metabolic, and microbiome-related profiles, changes did not occur at a steady rate.

Instead, most profiles followed non-linear patterns, with biological changes clustering during specific periods rather than progressing evenly year by year.

Two periods of pronounced biological change

The study identified two distinct age periods during which many biological profiles changed simultaneously. These periods occurred at approximately:

• 44 years of age
• 60 years of age

During both phases, coordinated biological changes were observed across multiple biological levels, including molecular profiles and microbiome-related measures. These findings are based on longitudinal analyses in which the same individuals were followed over time.

The researchers describe these periods as phases of adulthood during which aging-related biological changes are more pronounced than in other age ranges.

What do these findings mean for our understanding of aging?

The study suggests that biological aging does not necessarily progress evenly throughout adulthood but may be more pronounced during specific life phases, where multiple biological systems change simultaneously. At the same time, it is important to view the findings critically. Although the study is extensive and based on repeated measurements over several years, it includes only healthy adults from a single geographic region in California. The results therefore cannot be directly generalized to all populations.

The study also does not explain why these phases occur or what their direct implications are for health or functional ability. Still, it provides valuable insight into the complexity of aging and offers an important foundation for further research into how biological changes unfold across the adult lifespan.

What can you do to support healthy aging?

Although the study does not examine specific interventions, a large body of research shows that healthy aging is closely linked to biological processes such as declining NAD⁺ levels, increased oxidative stress, low-grade chronic inflammation, and gradual changes in telomere stability. Our understanding of these mechanisms continues to evolve, providing a clearer picture of what supports the body’s functions over time.

Fundamental factors such as sleep, nutrition, physical activity, mental well-being, and managing long-term stress are already known from research to play a central role in healthy aging. For some, targeted dietary supplements may also form part of a long-term approach, particularly when developed with a focus on biological mechanisms, quality, and scientific evidence.

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