Could the size of your head be a predictor of dementia in later life? This intriguing possibility has emerged from a study conducted by researchers in Texas, who delved into three decades of health data and brain autopsies from nearly 700 elderly nuns across the United States.

These nuns, who shared similar lifestyles characterized by healthy eating, a strong sense of community, and an absence of harmful substances like alcohol, surprisingly still saw about 17 percent of their group develop dementia by their life’s end.

The researchers discovered that nuns who possessed both lower levels of education and smaller head circumferences were four times more likely to suffer from dementia compared to those with higher education and larger heads. This correlation was highlighted in a series of studies that provided deeper insights into the potential risk factors for dementia.

Additionally, the findings indicated that participants with dementia often had a smaller hippocampus, which is crucial for memory retention. This key detail supports the theory that reduced head and brain sizes may lower the number of essential brain cells, making individuals more susceptible when these cells become impaired with age and dementia-related conditions.

Experts suggest that a smaller brain offers less of a protective buffer against neurocognitive diseases, underscoring the importance of understanding the interplay between physical brain characteristics and cognitive health.

Experts believe having a smaller head and brain reduces the amount of vital brain cells a person has, so when those cells become damaged with age and precursors to dementia, there is less of a buffer to protect against neurocognitive diseases. 

Limited education, meanwhile, has long been linked to dementia, as learning helps strengthen connections between brain cells and increases the likelihood of following healthy habits. 

Most head development occurs in early childhood, showing that dementia prevention starts well before symptom onset.  

The size of a person’s head may increase their risk of developing dementia, a study suggests (stock image)

The findings comes as Alzheimer’s disease, the most common form of dementia, strikes nearly 7million Americans, with that figure set to nearly double by 2050.

The study participants were taken from The Nun Study, which started in 1991 and includes 678 Catholic nuns from seven cities across the US.

Participants were between 75 and 102 years old, and the average age was 83. 

All of them agreed to donate their brains upon death for study. 

All of them came from the same order with the same housing, income, nutrition and access to healthcare, and most had the same level of education. 

Nuns also avoid alcohol and smoking, major risk factors for dementia. 

Along with analyzing donated brains, researchers looked through medical and dental records, as well as autobiographies written by the sisters as young adults before they took their vows. 

Each sister also had yearly neurological exams and cognitive assessments, including exercises on word recall and recognition and basic daily living tasks. 

Rebecca Luna’s (pictured here) early-onset Alzheimer’s symptoms appeared in her late 40s. She would black out mid-conversation, lose her keys and leave the stove before returning to find her kitchen full of smoke

Cognitive tests at the start of the study showed 118 participants, or 17 percent, had signs of mild cognitive impairment, a precursor to dementia, and 80 met the criteria for dementia at baseline. 

Of the 334 participants who were followed up with two decades after the start of the study, 39 percent had severe cognitive impairment. 

Based on health records and brain autopsies, the researchers found participants with both low education levels and a smaller head circumference were four times more likely to be diagnosed with dementia compared to those who were more educated and had larger heads. 

However, having just one of those factors alone did not significantly raise dementia risk. 

Scientists believe a larger head circumference, which also indicates a bigger brain, provides a ‘cognitive reserve’ of extra brain cells and connections. When brain cells become damaged with age, a larger brain is able to withstand it easier than a smaller brain. 

Jana Nelson was 50 when diagnosed with early onset dementia, following severe personality changes and a sharp cognitive decline that left her unable to solve simple math problems or name colors

Education, meanwhile, helps the brain form more complex networks and a greater cognitive reserve. It has also been shown to strengthen connections between brain cells. 

People with a higher education level are also more likely to follow healthy habits such as a balanced diet, exercise and not smoking, all of which have been tied directly to dementia and overall brain health. 

About 90 percent of head growth occurs before age six, and the brain reaches about 75 percent of its adult size by an individual’s first birthday. 

The average head circumference is generally 21.7 inches (55 cm) for women and 22.5 inches (57 cm) for men. 

Prenatal factors such as a mother’s nutrition, weight and history of substance abuse may influence head size, and exposure to environmental toxins like lead may stall growth. 

The researchers wrote that ‘findings from the Nun Study underscore the fact that cognitive health and prevention of dementia is a life-long task and not limited to the later years of life.’