Depending on your preferred authority, “middle age” begins at 40 or 45, and ends 20 years later at the beginning of “old age.” These years are a time of transition across the population, particularly in physical status. But what if an individual’s proteins offer a different take on the meaning of middle age (and even old age)?

Recently, an international team reported in Nature Medicine that how we view middle age is likely wrong (Lehallier et al., 2019). Using the SomaLogic technology, they looked at changes in thousands of circulating proteins among 4,263 healthy adults, spanning the ages of 18 to 95 years old. In digging through all those proteins, they uncovered a “proteomic clock” that marks the passage of biological time. Specifically, the team identified three events that happen in adulthood. The first aging event happens around 34 years of age. The second one occurs at 60 years of age, which was termed “middle age” by the authors. And the third one appears at 78 years of age, heralding the start of “old age.”

The researchers noted other fascinating phenomena. For example, their work confirms previous suggestions that people can be biologically younger than the age stated on their identification card. They also noted that people who performed well on cognitive and physical tests tended to age slower according to their protein profiles, and that women aged slower than men.

On the flip side, the researchers found that it is also possible to age faster. For example, the protein patterns in people with Alzheimer’s disease or Downs Syndrome resembled the patterns associated with the proteome of older people, which could help explain the rapid aging seen in these disorders.

So, perhaps 40 or 45 are not really middle age and 60 or 65 even are not old – at least from a biological perspective! A lovely thought one can have even if your birthday cake is highly illuminated.

References

Lehallier, B., Gate, D., Schaum, N., Nanasi, T., Lee, S. E., Yousef, H., . . . Wyss-Coray, T. (2019). Undulating changes in human plasma proteome profiles across the lifespan. Nat Med, 25(12), 1843-1850. doi:10.1038/s41591-019-0673-2