Our Body Parts Don’t Age At The Same Rate

By Joelle Renstrom | 8 years ago

biological clockAccording to new research conducted by a UCLA scientist, even though my brain is 35, my breasts are pushing 40 and my heart hasn’t hit 30. I’m assuming that means I can pick whatever number I want when someone asks my age, but the study doesn’t actually address that detail.

While we’re all familiar with the concept of a biological clock, what we might not realize is that this isn’t just a societal or cultural construct designed to pressure women to have babies — the concept is based on data that indicates that our cells actually have expiration dates, which is basically the number of times they can multiply before they start degrading. This accounts for people who have a biological age that’s higher or lower than their actual chronological age. New research indicates that it isn’t just people that age at different rates — different body parts on the same person age differently too.

UCLA’s Steve Horvath, professor of human genetics and biostatics, has published a study in Genome Biology in which he details how he figured out a way to calculate the age of different organs, cells, and tissues within the same body. Horvath focused on methylation, a natural process that changes DNA’s chemical make-up and is important to cellular development and differentiation. Methylation accounts for the suppression of viral genes and other undesirable biological factors, but is also involved in aging and age-related diseases, such as cancer.

Because rates of aging are affected by the ways our DNA changes after we’re born, Horvath studied more than 120 sets of genomic data, including 8,000 samples that spanned 51 different types of cells and tissues, both healthy and cancerous. He examined the association between methylation and age, tracking samples from the womb to 100 years old. He was able to identify 350 genetic markers located in the body that vary with age. Horvath then contrasted the biological age of the samples to their chronological age and found that the “clock” he developed “reliably keeps time across the human anatomy.”

Most of the samples had matching biological and chronological ages, but there were a few that varied pretty drastically. He found that women’s breast tissue in particular ages two to three years faster than any other part of the body if they’re healthy, but if they’re cancerous, they present as about 12 years older than the rest of the body. This may explain why breast cancer occurs more than any other kind of cancer in women. Cancers in general reflect a far older age than their healthy counterparts — roughly 36 years older, according to Horvath. This is consistent with the large role age plays in the development of cancer.

The youngest parts of the body are stem cells, which Horvath refers to as “newborns.” He also believes that transforming mature cells into pluripotent stems cells, which essentially means reprogramming them into something akin to an embryonic stem sell that can then become any type of cell, “rests the cells’ clock to zero.” This may signify a major breakthrough in anti-aging technology and raises the possibility of actually reversing the aging process without having to find a mythical fountain. Thus, the biological clock might become an important biomarker.

Another interesting detail in Horvath’s study is that the rates of aging don’t stay the same throughout our lives. The biological clock moves faster early on, and then slows down to a more constant speed when we close out our teenage years. I guess that explains why I was an old soul at age seven. It also means that the disbelief and denial we feel as we age — how is it possible I graduated from college nearly 15 years ago? — can be validated, at least a little bit, by science. Age is, indeed, just a number. Or rather, a whole bunch of numbers.