Obesity significantly reduces blood flow to the brain, a new Irish study has found.

However, increased physical activity can positively modify, or even negate, this reduced blood flow, according to scientists at The Irish Longitudinal Study on Ageing (TILDA) at Trinity College Dublin. This is an ongoing study of people over the age of 50 in Ireland.

Figures from the World Health Organization (WHO) show that over one billion adults worldwide are currently overweight, while 300 million are clinically obese. Previous TILDA research has shown that over one-third of Irish adults aged 50 and older are obese and a further 43% are overweight.

Obesity can have a major impact on physical and mental health. Furthermore, the increased strain it puts on the immune system is particularly important given the current Covid-19 pandemic.

The study looked at three different measures of obesity – body mass index (BMI), waist-to-hip ratio and waist circumference. It also looked at physical activity levels in those over the age of 50.

The flow of blood in the brain was measured using cutting-edge MRI scanning and analysis techniques.

The study found that increased BMI, waist-to-hip ratio and waist size were all associated with less blood supply to the brain.

While brain blood flow is known to decline with age, the scientists found that the negative influence of obesity on brain blood flow was greater than that of age.

They noted that a waist size increase of just one additional centimetre was associated with the same reduction in brain blood flow as being an additional year older.

However, higher levels of physical activity were found to modify the links between reduced brain blood flow and obesity.

The scientists recommended that people should try to achieve at least 90-120 minutes of ‘being active’ throughout the day, engaging in activities that require moderate effort, such as fast walking or cycling. However, they also emphasised that any increase in physical activity, such as gardening, should help maintain and possibly improve blood flow to the brain.

“Our study not only shows that there is a link between obesity and reduced brain blood flow, but also that it is possible to protect against the negative consequences of obesity through regular physical exercise.

“Whereas these findings are of relevance in the global context, because of the rapidly evolving global burden of obesity, the research is especially important to Irish adults because obesity and being overweight is a considerable health issue in Ireland,” commented TILDA principal investigator and the study’s co-author, Prof Rose Anne Kenny.

According to Dr Silvin Knight, research fellow at TILDA and the study’s lead author, consistent, healthy blood supply is critical because it ensures that the brain is provided with enough oxygen and nutrients to function correctly.

“If brain blood flow becomes impaired, it can lead to serious health issues as we age, such as increasing the risk of dementia. We know that obesity can predispose a person to age-related conditions, illness, and disease, and even reduce life expectancy by up to six years in men and seven years in women, after the age of 40,” he explained.

Prof Kenny added that these findings can be used “to prepare meaningful public health policies that will promote impactful and positive lifestyle habits, such as regular physical activity, to mitigate against some of the negative consequences of the growing obesity crisis”.

Details of the findings are published in the journal, Neurobiology of Aging.