Human aging accelerates dramatically at age 44 and 60

The human body does not age at a constant rate throughout adulthood — instead, it accelerates dramatically around ages 44 and 60, a new study finds.

The new research, published Aug. 14 in the journal Nature Aging,involved measuring more than 11,000 molecules in the adult body over time, and it revealed that 81% of them undergo dramatic changes at these two ages.

This type of aging research focuses on tracking "biological age," which refers to changes that occur in the body over a lifetime, affecting proteins, metabolites and gene activity. This concept is distinct from the "chronological age" that people celebrate each year on their birthdays.

Finding that biological aging accelerates at two points in midlife could help researchers understand why the risk of certain illnesses increases in fits and starts as chronological age rises. For example, approximately 6.5% of people ages 40 to 59 have coronary artery disease, but the prevalence rises sharply to 19.8% in people ages 60 to 79.

Related: Natural rates of aging are fixed, study suggests

For the study, researchers at Stanford University recruited 108 participants that were of diverse ethnic backgrounds and ranged from 25 to 75 years old. Every three to six months for several years — up to about seven years in total — the scientists collected blood samples from the participants to assess how different factors, such as gene activity and blood sugar levels, varied over time.

Many of the factors that shifted around age 44 and 60 were related to heart Health. For example, a protein linked to atherosclerosis, or plaque buildup in arteries, increased in the blood of participants during their 40s and 60s. These age groups also showed declines in the ability to metabolize caffeine, which temporarily raises blood pressure, and alcohol, which initially lowers but then raises blood pressure.