It's well established that our most vital organ, the heart, doesn't necessarily age at the same rate as we do—based in part on lifestyle factors, some of us have hearts that are older or younger than our chronological age.

Now researchers are reporting in the journal Cell Systems that different parts of our bodies can age at different rates and in different ways. When looking at the livers and brains of rats, researchers found that—because liver cells divide and are regularly replaced while most brain cells remain in tact for life—more proteins in the brain are affected by aging than in the liver, making it an essentially "older" organ over time.

"Based on our findings, we would define aging as an organ-specific deterioration of the cellular proteome," one study author says in a Eureka Alert release.

In fact they found 468 differences in "protein abundance" between young and old animals, and another set of 130 proteins showed age-related changes that may affect the protein's functions or activity levels.

The research is important because insights into how organs age can shed light on age-related disease, notes Healthline. "An interesting open question is whether one organ can affect the aging of another organ," says the researcher.

"Answering this question would give us a more comprehensive understanding of the aging process and how it relates to disease." (Odds are your heart is at least five years older than you are.)

This article originally appeared on Newser: Your Liver Is Younger Than Your Brain

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