Human brains are getting bigger: Could this lead to lower dementia risk?

• Dementia is a growing problem worldwide, with numbers predicted to almost triple over the next 30 years.
• The rise is generally attributed to the growing aging population, but lifestyle can also contribute.
• However, a new study suggests there may be some good news in the field of dementia.
• It found that people’s brains have been getting more prominent over the past 100 years, and this increased brain reserve could, potentially, reduce the risk of age-related dementias.

In all types of dementia, as brain cells are damaged and die, there is some degree of brain shrinkageTrusted Source, with this being particularly pronounced in Alzheimer’s disease and vascular dementia. 

Human brain sizes are increasing.

This study looked at participants in the Framingham Heart Study (FHS), a long-term study that has followed 15,000 individuals for over 75 years.

Of the FHS cohort, 3,226 people had two MRI scans suitable for this study. Of them, 1,706 (53%) were women, and 1,520 (47%) were men. The scans measured intracranial volume (ICV), cortical gray matter, cerebral white matter, hippocampal volume, surface area, and thickness.

The participants were all born between 1930 and 1970, with the median decade of birth being the 1950s. On average, people born in the 1970s were 1.6 inches taller than those born in the 1930s, so the researchers adjusted for this when comparing brain measurements.

People born in the 1970s had more significant brain volumes than those born in the 1930s.

They had a 6.6% greater ICV, 7.7% more white matter, 2.2% more cortical gray matter, 5.7% greater hippocampal volume, and 14.9% larger cortical surface area. The one measure that had decreased was cortical thickness, which was 20.9% lower. These differences remained significant when the researchers adjusted for height differences.

“The decade someone is born appears to impact brain size and potentially long-term brain health,” said Charles DeCarli, MD, first author of the study, distinguished professor of neurology, and director of the UC Davis Alzheimer’s Disease Research Center in a press release. 

“Genetics plays a major role in determining brain size, but our findings indicate external influences — such as health, social, cultural and educational factors — may also play a role,” he said.

Larger brain size may indicate lower dementia risk

Previous trusted Sources have suggested that larger brain volume protects against the effects of dementia pathology, arguing that those with a greater head circumference can endure a greater degree of damage before they start to show cognitive impairment.

This ‘brain reserve hypothesis’Trusted Source suggests that a larger brain volume, with more neurons and synaptic connections, could protect against cognitive decline from brain atrophy. Experts use ICV on MRI and head circumference as indicators of brain volume.

However, this observed effect could be due to other factors, as Ismail told GMHCN: Other studiesTrusted Source have stressed that cognitive reserve — how well the brain functions — is more important than brain size in dementia risk. People with a higher cognitive reserve tend to show dementia symptoms later but then decline faster once symptoms become evident. 

The researchers in this study suggest that the increase in brain volumes over the four birth decades in their research could predict a lower risk of dementia in people born later in the FHS. 

Call for more diverse studies.

The researchers acknowledge that their study cohort was predominantly non-Hispanic White, healthy, and well-educated, so not representative of the general population of the United States. However, they emphasize that the study’s strengths include its following three generations spanning over 80 years of births.

Ismail called for further studies that include a greater diversity of people: “This is particularly important given the known sociocultural and health disparities that exist in underrepresented populations,” he added.

The Alzheimer’s Association’s U.S. Study to Protect Brain Health Through Lifestyle Intervention to Reduce Risk (U.S. POINTER), which should publish results next year, aims to help address this gap in the research, as Ismail told GMHCN:

“In the U.S. POINTER Study, more than 2,000 volunteer older adults at increased risk for cognitive decline are enrolled and will be followed for two years. Nearly 30% of current participants are from populations historically underrepresented in Alzheimer’s/dementia research.”

As healthy people age, the brain decreases slightly in size. However, in people with dementia, as nerve cells are damaged and die, many regions of the brain shrink, a process known as brain atrophy. So, could a larger brain help reduce a person’s risk of dementia?

A new study from UC Davis Health has suggested that it might. Researchers found that people born in the 1970s had brains that were, on average, 6.6% larger than those born in the 1930s. They suggest that larger brain size means increased brain reserve — which may reduce the risk of age-related dementias.

JAMA Neurology, a trusted source, published the study. Dementia’s effects on the brain

Currently, around 58 million trusted Source people worldwide have dementia, and that number is projected to reach 152.8 million by 2050.

Although some memory loss is a natural part of aging, dementia is not. Dementia describes a range of diseases, with the most common being Alzheimer’s disease, causing 60-80% of cases. Others include vascular dementia, Lewy body dementia (which may be associated with Parkinson’s disease), frontotemporal dementia, and mixed dementia.

Symptoms of dementia, which worsen over time, may include: memory problems asking the same question repeatedly, difficulty finding or understanding words feeling confused in unfamiliar environments, issues dealing with money and numbers, anxiety and withdrawal, difficulty planning and carrying out tasks, mood, personality, and behavior changes sleep disturbances obsessive tendencies.