NBC News
For many people, reaching their mid-40s can bring with it unpleasant signs that the body is no longer functioning as well as it once did. Injuries seem to occur more frequently. Muscles seem weaker.
A new study, published Wednesday in the journal Nature Aging, shows what may be causing this physical decline. Researchers have found that molecules and microorganisms both inside and outside our bodies undergo dramatic changes, first around age 44 and then again by age 60.
And these alterations may be generating significant differences in cardiovascular health and immune function.
The study’s findings come from Stanford scientists who analyzed blood and other biological samples from 108 volunteers between the ages of 25 and 75 who donated samples over several years.
“While it’s obvious that you age throughout your life, there are two major periods when things really change,” said senior study author Michael Snyder, a professor of genetics and director of the Center for Genomics and Personalized Medicine at Stanford Medicine.
For example, “there is a big change in lipid metabolism when people reach 40 years old and in carbohydrate metabolism when they reach 60,” he explained.
Lipids are fatty substances, such as LDL, HDL and triglycerides, that perform a multitude of functions in the body, but can be harmful if they accumulate in the blood.
The scientists tracked many types of molecules in the samples, including RNA and proteins, as well as the participants’ microbiomes.
The metabolic changes discovered by the researchers do not indicate that 40-year-olds burn calories more slowly, but rather that their bodies break down food differently. Scientists are not sure what the exact impact of these changes is on health.
Previous research showed that resting energy expenditure, or metabolic rate, did not change between ages 20 and 60. The results of the new study do not contradict that.
Changes in metabolism impact the body’s reaction to alcohol or caffeine, although the health consequences are still unclear. In the case of caffeine, it may cause increased sensitivity.
It’s also not yet known whether the changes might be related to lifestyle or behavioral factors. For example, changes in alcohol metabolism might be due to people drinking more in their mid-40s, Snyder said.
For now, Snyder suggested that people in their 40s keep a close eye on their lipids, especially LDL cholesterol.
“If they start to go up, they may want to consider taking statins, if their doctor recommends it,” he said. Also, “knowing that there is a change in the molecules that affect the muscles and the skin, they may want to warm up more before exercising, so they don’t hurt themselves.”
Until we know more about what these changes mean, the best way to cope would be to eat healthy foods and exercise regularly, Snyder added.
Dr. Josef Coresh, founding director of the Institute for Optimal Aging at NYU Grossman School of Medicine, compared the new findings to the invention of the microscope.
“The beauty of this kind of work is the level of detail we can see in molecular changes,” added Coresh, a professor of medicine at NYU. “But it will take time to figure out what individual changes mean and how we can tailor drugs to those changes. We know that the onset of many diseases is in middle age, when people are in their 40s, although the disease can appear decades later.”
The new study “is an important step forward,” said Dr. Lori Zeltser, a professor of pathology and cell biology at Columbia University’s Vagelos College of Physicians and Surgeons. Although we don’t yet know what the consequences of these metabolic changes are, “right now, we have to recognize that We metabolize food differently at age 40, and that’s something really new”.
The changes discovered by the researchers could help explain numerous age-related health changes, such as loss of muscle mass, because “the body breaks down food differently,” Zeltser added.
