In the study, female mice exercising before and during pregnancy influenced the health of their future offspring and their offspring’s offspring, even if those offspring never exercised at all.
While you may think a mouse study isn’t relevant to humans, the idea that one generation’s way of life shapes the next generation’s health is “pretty well recognized” scientifically, said Laurie Goodyear, a professor of medicine at Harvard Medical School. and principal investigator at the Joslin Diabetes Center in Boston, who oversaw the new study.
In animal and human studies, poorly nourished mothers and fathers who develop diabetes, obesity and other metabolic disorders often pass on a predisposition to those conditions to their children, he said. This propensity is independent of education and lifestyle. In other words, babies born to parents with metabolic problems tend to develop those same conditions as adults, even if, until then, they had been eating well and staying slim.
Scientists call this process developmental programming. They I suspect it depends both on the environment inside a mother’s womb during pregnancy and on epigenetics, or small changes in how our genes work, based on how we eat and live. These epigenetic changes can be passed on to offspring by the mother or father, affecting children’s risks for various diseases.
But Goodyear and other researchers have found that exercise also contributes to developmental timing, in a more welcome way. Studies his laboratory and others show that if mother mice run before mating and during pregnancy, their babies are protected to some extent from developing obesity and diabetes as they grow older, even if they eat high-calorie food and don’t exercise.
Parents who run before mating may also pass on more robust metabolisms to their offspring, whether or not their mothers exercise, and, in a 2018 studyRunning males fathered pups with healthier brains from birth than mice fathered by sedentary fathers.
But studies hadn’t investigated whether these protections might be long-lasting enough to show up in grandchildren, even if their parents are sedentary.
So for the new study, published in June in Molecular Metabolism, Goodyear and his colleagues had young female mice run on wheels. Some ate normal food, others an unhealthy, high-fat diet. Another group of female mice on the same diets did not run. All of the females were then bred to sedentary males, and the runners continued to exercise throughout their subsequent pregnancies. (Mice seem to enjoy running, and even when heavily pregnant, they scoot on their wheels for a mile or so most days.)
They duly gave birth. However, none of their youngsters ran to keep their metabolism relatively neutral, free from epigenetic and other changes initiated by exercise. The researchers hoped, in this way, to trace the effects of their mothers’ exercise across this sedentary generation. For the same reason, they bred only males from this middle generation, eliminating any potential effect of womb conditions on the babies.
The resulting grandchildren, male and female, also remained sedentary and ate normal food throughout their lives.
But from birth, the mice with active grandmothers were slimmer than the others, and the males had denser, healthier bones. Most interestingly, as the animals moved into middle age, those with inactive grandmothers began to develop poor blood sugar control and worsening insulin sensitivity, indicating possible early-onset diabetes. These conditions are common with age and inactivity, both in rodents and people.
But they didn’t appear if Grandma ran. Mice with an active grandmother maintained relatively healthy blood sugar control and insulin sensitivity well into old age, despite being inactive. (Their running grandmothers’ diets, high-fat or normal, hadn’t mattered, the researchers also found, only their exercise.)
“It was remarkable,” said Ana Alves-Wagner, a senior postdoctoral fellow at the Joslin Diabetes Center and Harvard Medical School, who led the new study. “Exercise had improved the metabolic health of several generations.”
Obviously, this was a mouse study and impossible to repeat in people, requiring decades of time and draconian coercion over people’s activities, diets, and mating choices. Nor did it examine how, at the molecular level, exercise reshaped the animals’ biology so pervasively that the effects reappeared in subsequent generations.
But Goodyear believes that epigenetics is a key factor and that the results likely apply to us, he said, since we share many aspects of our metabolism and physiological responses to exercise with mice.
If so, the findings become practical and poignant.
“I was so intrigued when I heard about this study,” said Daniel Lieberman, a professor of human evolutionary biology at Harvard University who studies how physical activity shaped our species during evolution. “Our metabolisms seem to be adapted to respond to environmental signals over multiple generations. We do not yet know the mechanisms by which this occurs in mice. Regardless, this study reinforces the view that when we exercise, we’re not just doing it for ourselves.”
The study, of course, is not meant to criticize any potential mother or father who is unable or chooses not to exercise before having children, Goodyear said. But the results offer those of us who choose to work out one more reason. We may walk or ride horses today for the sake, in part, of tomorrow’s anticipated grandchildren.
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