Our growing brains could help lower risks of dementia
Human brains are gradually getting bigger, decade by decade, potentially lowering people’s risk of developing age-related dementia, according to a recent study published by Alzheimer’s researchers at UC Davis Health.
People born in the 1970s have more brain volume and more brain surface area than people born in the 1930s, according to the study, published March 25 in JAMA Neurology.
“Our brains are growing and that’s a good thing,” said Dr. Charles DeCarli, first author and director of the UC Davis Alzheimer’s Disease Research Center.
More brain volume and surface area means more “brain reserve” — which acts as a sort of buffer if one loses some brain function due to injury — and researchers believe this gradual increase could mean the overall population’s risk of developing age-related dementia is dropping. The study also showed gradual increases in brain structures where connections between and among nerve cells occur that are important for cognition.
“Think of it like a hybrid car,” DeCarli said. “If the battery runs out, you still have the gas engine.”
The reasons brains are getting larger are believed to be linked to improvements in the early childhood environment at the population level, including better prenatal care, nutrition, health care and education.
Increasing brain size could be one reason why the incidence of age-related dementia is declining, even though the overall number of people diagnosed with dementia is rising.
An estimated 7 million Americans are living with Alzheimer’s disease, and that is expected to rise to 13 million by 2050, according to the Alzheimer’s Association. But there’s been a 20% drop in the incidence of dementia — newly reported cases as a proportion of the population — each decade since the 1970s, according to a 2016 study in the New England Journal of Medicine.
The 2016 study included about 5,200 U.S. adults 60 and older who participated in the Framingham Heart Study, a landmark continuing study begun in 1948 to study cardiovascular disease among healthy adults in Framingham, Mass.
The UC Davis research examined MRI images of the brains of about 3,200 healthy U.S. adults between 1999 and 2019. The average age at the time of the MRI was 57.
Researchers found that brain volume and surface area grew gradually but consistently in people who were born in each subsequent decade between the 1930s and 1970s. People born in the 1970s had 6.6% more average brain volume than those born in the 1930s — 1,321 milliliters compared with 1,234 milliliters, the analysis found. And people born in the 1970s had nearly 15% more average brain surface area — 2,104 square centimeters compared with 2,056 square centimeters.
It’s not clear whether the trend is continuing in people born after the 1970s.
There are some caveats to the findings. The study participants are part of the Framingham Heart Study, which initially included only healthy adults. The study subsequently included the children of the original cohort and the children’s spouses and, later, the generation after that. The participants are generally healthy and motivated to participate in scientific research, and not representative of the world or even the U.S., DeCarli said.