Age is more than just the number of candles on a birthday cake. In fact, the number of birthdays you’ve had may not be the most accurate way to determine how old your body is.
Instead, scientists are looking to measure biological age. Whereas chronological age is the number of years since you were born, biological age is the age of your body based on your physical health status. With biological factors considered, biological age may not only be a better predictor of how old an individual is — what if you are actually older or younger than you think you are? — but it also may be a better predictor of lifespan and health.
There are many ways to calculate biological age, such as through glucose levels, cholesterol levels, and even walking speed. But over the last decade, scientists have found that DNA has wrinkle patterns of its own: the epigenome.
Think of the epigenome as accessories that our DNA wears or takes off to turn genes on and off. These epigenetic modifications are critical for cell differentiation and are responsible for the subtle differences between identical twins and for the spots on calico cats.
Steve Horvath, Ph.D., a UCLA aging researcher and an Allen Distinguished Investigator, studies a form of epigenetic modification known as methylation, in which methyl groups — small chemical tags — are attached to DNA. As we age, our methylation patterns change in predictable ways: Certain DNA regions lose methylation, while others gain methylation. By measuring and averaging those patterns, Horvath created in 2013 the first test that could predict epigenetic age (an aspect of biological age) across multiple human tissues — a test he dubbed the epigenetic clock.
