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A new study has shown that the human body does not age at a constant rate throughout adulthood; instead, the process accelerates significantly between the ages of 44 and 60.
The study, published August 14 in the journal Nature Aging, involved analyzing more than 11,000 molecules in the adult body over time and found that 81 percent of them undergo significant changes between the two age ranges.
These studies of aging focus on tracking “biological age,” which refers to changes that occur in the body throughout life, affecting proteins, metabolites, and gene activity. This concept is different from the “chronological age” that people mark each year on their birthday.
The discovery that biological aging accelerates at two points in midlife may help scientists understand why the risk of certain diseases increases dramatically with increasing chronological age. For example, about 6.5 percent of people aged 40 to 59 have coronary artery disease, but that prevalence increases sharply to 19.8 percent in people aged 60 to 79.
For the study, a team of Stanford University researchers recruited 108 participants of varying ethnic backgrounds, ages 25 to 75. Every three to six months for up to seven years, the researchers collected blood samples from the participants to assess how factors including gene activity and blood sugar levels changed over time.
Many of the factors that changed between ages 44 and 60 were related to heart health. For example, levels of a protein linked to atherosclerosis, or plaque buildup in the arteries, increased in the blood of participants at ages 40 and 60. These age groups also showed a decreased ability to metabolize caffeine, which temporarily raises blood pressure, and alcohol, which initially lowers and then raises blood pressure.
The body's ability to produce unsaturated fatty acids, which help lower “bad” cholesterol levels, also decreased during these two age periods.
While the study's many links to cardiovascular health were only correlational, they highlight potential reasons why heart disease becomes more common with age.
In addition to heart health problems, blood sugar levels peaked in participants at ages 40 and 60, which may indicate a link to age-related type 2 diabetes.
Scientists have not yet determined why body chemistry changes significantly at this age, and the study did not take into account the influence of lifestyle factors such as diet or physical activity.
Juan Carlos Veryan, who studies aging at the National Institute of Geriatrics in Mexico and was not involved in the study, told Live Science that “the inflection point at 60 is probably more related to inflammation.” For example, participants over 60 had a buildup of antioxidant enzymes in their blood. These enzymes neutralize chemical triggers of inflammation and suggest that inflammation may be accumulating in this age group.
Aging at 44 also coincides with the time when some women begin to go through perimenopause. However, “we found similar time trigger points for women and men,” indicating that sex-specific hormonal changes are not the cause of aging, said study co-author Xiaotao Shen, a computational biologist now at Nanyang Technological University in Singapore. Therefore, “there must be another factor causing the same changes in men and women.” What that common factor is remains unknown.
The study had limitations because the participants ranged in age from 25 to 75, so the researchers were unable to assess significant changes that occur at other key points in life, such as puberty or old age. The small sample size of 108 participants from California was also a limitation because the data
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