A new study shows that people of exactly the same age may experience very different molecular changes as they get older.
According to Live Science, Julia El-Sayed Moustafa, a researcher at King’s College London and one of the authors of the study, says molecular ageing is a dynamic and individual phenomenon. Even in two people born on the same day, the activity of a gene may increase in one and decrease in the other. Such differences are also observed in metabolites, the small molecules produced in the body’s chemical processes.
The findings complicate measuring ageing with a single metric. In recent years, "biological age" and "ageing clocks" have been used to estimate the actual cellular and physical state using molecular markers, including chemical changes on DNA. The new findings indicate that biological ageing is less a fixed number and more a set of variable molecular pathways, and different body systems may age at different rates.
Researchers examined 335 women aged 32 to 80 over eight years who participated in the long-term TwinsUK study. This cohort includes identical and non-identical twins and was established to study the effects of genetics and environment on health. Each participant visited the clinic at least three times between 2009 and 2017. At each visit, blood samples were taken and gene activity and metabolite levels were measured. Unlike many ageing studies that compare different people at a single time point, this study tracked individual changes over time.
Of more than 16,000 genes and 915 metabolites examined, 5,061 genes and 181 metabolites showed significant changes over time. Among these genes, 5,036 showed similar increasing or decreasing trends across the whole group; the same was true for 45 metabolites. Many of these genes were associated with immune function, metabolism, and age-related diseases, including heart disease and neurodegenerative disorders.
However, the pattern was not the same for everyone. Even when the activity of a gene or the level of a metabolite changed in one direction in most people, there were groups with the opposite trend. For 136 metabolites, the degree of change varied from person to person; a substance that increased in one woman might decrease in another or remain nearly stable. Also, the overall metabolite profile of each woman became less similar to her previous profile over time.
Several factors were associated with these molecular changes. Gene expression patterns in identical twins were more similar than in non-identical twins, indicating a genetic role. Different types of immune cells also showed different patterns of gene activity with age.
The timing and season of blood sampling also mattered. About a quarter of genes and metabolites showed seasonal changes, some of which were related to energy production and immune activity. Additionally, up to 40 percent of metabolites varied with the body’s 24-hour circadian clock.
Researchers also observed an unexpected decrease in levels of per- and polyfluoroalkyl substances (PFAS) in the blood. These synthetic compounds, known as "forever chemicals," have been used in products such as nonstick cookware and food packaging. The researchers suspect the decline may be due to restrictions on the use of these substances in the UK.
Overall, more than 100,000 associations between genes and metabolites were identified, indicating that changes in some genes are accompanied by changes in certain metabolites. The researchers say ageing cannot be considered an unpredictable phenomenon, but the process is highly individual and context-dependent.
This observational study included only women and relied solely on blood samples. The researchers plan next to extend the follow-up period of molecular changes from 8 to about 15 years.