1. Dementia is a growing problem worldwide, with numbers predicted to almost triple over the next 30 years.
2. The rise is generally attributed to the growing and aging population, but lifestyle can also contribute.
3. However, a new study suggests there may be some good news in the field of dementia.
4. It found that people’s brains have been getting larger over the past 100 years, and this increased brain reserve could, potentially, reduce the risk of age-related dementias.
As individuals age, the brain undergoes a slight reduction in size. Nevertheless, for individuals afflicted with dementia, various brain regions experience shrinkage due to damage and cell death, a phenomenon termed brain atrophy. Hence, could possessing a larger brain potentially mitigate one's susceptibility to dementia?
According to a recent investigation conducted by UC Davis Health, this proposition seems plausible. The study reveals that individuals born in the 1970s exhibited brains that were, on average, 6.6% larger than those born in the 1930s. The researchers postulate that a greater brain size implies heightened brain reserve, potentially lowering the risk of dementias associated with aging.
The study is published in JAMA Neurology Trusted Source.
“While these newly published results add to the body of literature on brain size and changes over time, this study was largely conducted in healthy, well-educated, non-Hispanic White individuals, and so [these findings] are not necessarily generalizable to other groups or individuals.”
— Ozama Ismail, PhD, Alzheimer’s Association director of scientific programs, who was not involved in the study.
Dementia’s effects on the brain
Presently, approximately 58 million individuals globally are affected by dementia, a figure anticipated to soar to 152.8 million by 2050.
While certain degrees of memory decline are intrinsic to the aging process, dementia stands apart. Dementia encompasses a spectrum of disorders, with Alzheimer's disease, the predominant form, contributing to 60-80% of instances. Additional variants include vascular dementia, Lewy body dementia (potentially linked to Parkinson's disease), frontotemporal dementia, and mixed dementia.
Symptoms of dementia, which worsen over time, may include:
1. memory problems
2. asking the same question repeatedly
3. difficulty finding or understanding words
4. feeling confused in unfamiliar environments
5. problems dealing with money and numbers
6. anxiety and withdrawal
7. difficulty planning and carrying out tasks
8. mood, personality and behavior changes
9. sleep disturbances
10. obsessive tendencies
Across all dementia types, there exists a degree of brain atrophy due to cell deterioration and death, with Alzheimer's disease and vascular dementia showing particularly notable shrinkage.
Human brain sizes are increasing
This research examined subjects from the Framingham Heart Study (FHS), a comprehensive investigation spanning over 75 years and involving 15,000 participants.
Within the FHS cohort, 3,226 individuals underwent two MRI scans deemed suitable for this analysis. Among them, 1,706 (53%) were females, and 1,520 (47%) were males. The scans assessed various metrics including intracranial volume (ICV), cortical gray matter, cerebral white matter, hippocampal volume, cortical surface area, and cortical thickness.
All participants were born between 1930 and 1970, with the median birth decade being the 1950s. Individuals born in the 1970s averaged 1.6 inches taller than those born in the 1930s, prompting researchers to adjust for this discrepancy when comparing brain metrics.
People born in the 1970s had greater brain volumes than those born in the 1930s.
They exhibited a 6.6% increase in ICV, 7.7% augmentation in white matter, 2.2% rise in cortical gray matter, 5.7% expansion in hippocampal volume, and a 14.9% enlargement in cortical surface area. The lone exception was cortical thickness, which experienced a 20.9% reduction. These variances retained significance even after adjusting for height disparities.
"The era of birth appears to exert influence on brain dimensions and potentially long-term brain well-being," remarked Charles DeCarli, MD, lead author of the study, esteemed professor of neurology, and head of the UC Davis Alzheimer’s Disease Research Center, as stated in a press release.
"While genetics undoubtedly plays a significant role in determining brain size, our findings suggest that external factors—such as health status, societal, cultural, and educational influences—might also contribute," he added.
“Larger brain structures like those observed in our study may reflect improved brain development and improved brain health. A larger brain structure represents a larger brain reserve and may buffer the late-life effects of age-related brain diseases like Alzheimer’s and related dementias.”
— Charles DeCarli, MD
Larger brain size may indicate lower dementia risk
Earlier research has proposed that increased brain volume may serve as a shield against dementia-related pathology, contending that individuals with larger head sizes can withstand a higher level of damage before experiencing cognitive decline.
Referred to as the 'brain reserve hypothesis,' this theory posits that a larger brain volume, characterized by a greater number of neurons and synaptic connections, may offer defense against cognitive deterioration stemming from brain atrophy. Clinicians utilize intracranial volume (ICV) on MRI scans and head circumference as metrics for assessing brain volume.
Nonetheless, the observed phenomenon might be influenced by other variables, as Ismail conveyed to Medical News Today:
“Larger brain volumes may be beneficial in maintaining resilience to cognitive decline and dementia, but many other factors can contribute to resilience, including genetics, environment, socioeconomic status, education, and active vs. sedentary lifestyle.”
Additional investigations have underscored the significance of cognitive reserve—reflecting the brain's functional capacity—as more crucial than mere brain size concerning dementia susceptibility. Individuals with elevated cognitive reserve typically manifest dementia symptoms at a later stage but experience a swifter decline once symptoms manifest.
The scientists involved in this study propose that the surge in brain volumes across the four decades of birth examined in their research may forecast a diminished dementia risk among individuals born later within the Framingham Heart Study (FHS) cohort.
Call for more diverse studies
The researchers recognize that their study sample primarily consists of non-Hispanic White individuals who are healthy and possess high levels of education, thus not reflecting the broader demographics of the United States population. Nevertheless, they stress the study's robustness, highlighting its multi-generational scope spanning over 80 years of births.
Ismail advocated for future investigations encompassing a more diverse range of participants, urging for studies that incorporate a broader spectrum of individuals.
“More diversity in research populations is needed before conclusions can be made about changes in brain size over generations and the influence it may have on cognition, resilience, and dementia risk.”
"This is particularly crucial considering the well-documented social, cultural, and health discrepancies prevalent in marginalized communities," he remarked.
The Alzheimer's Association's U.S. Study to Safeguard Brain Health via Lifestyle Intervention to Lower Risk (U.S. POINTER), slated to unveil findings next year, aims to bridge this research void, as Ismail disclosed to MNT:
"In the U.S. POINTER Trial, over 2,000 older adults who are at heightened risk for cognitive decline have volunteered and will be monitored over a two-year period. Nearly 30% of current participants hail from demographics historically underrepresented in Alzheimer's/dementia research."
