According to the World Health Organization, the prevalence of obesity nearly doubled between 1980 and 2008. They report that more than 1.4 billion adults were overweight and more than half a billion were obese in 2008. At least 2.8 million people each year die as a result of health implications from being overweight or obese. While obesity was previously mostly associated with high-income countries, obesity is now also prevalent in low- and middle-income countries. The World Health Organization has gone as far as to label obesity a global epidemic.1
Diabetes, cancer, and cardiovascular disease have each been linked to obesity. Researchers have evaluated the negative health effects of obesity on not only these health conditions, but also the possible effects on the human brain as well. As life spans are lengthening and the number of older people continues to climb, these associations and the increased rate of obesity in the world population make it important to understand the full impact of obesity on brain health.
White matter volume was compared between lean and overweight or obese patients. The findings showed an average increase in ‘brain age’ of approximately 10 years for the overweight and obese individuals compared to lean patients. The results demonstrate that increased adipose (fat) has a significant impact on brain structure.
Researchers recruited 527 people between the ages of 20 and 87 years, who were cognitively healthy adults, from the local community over a period of 5 years as part of an ongoing project to investigate the effects of aging on memory and cognition at the Cambridge Centre for Aging and Neuroscience.2 Of these 527 people, 54 were excluded on the basis of being underweight, defined as a Body Mass Index (BMI) of less than 18.5kgm−1, under the age of 20, or for poor MRI scan quality.
The mean age of the participants was 54 years (range 20–87), and mean BMI was 26 kg/m2 (18.5–45.5). The final study group included 246 (51%) lean controls (BMI between 18.5–25 kgm−2), 150 overweight subjects (31%; BMI 25–30 kgm−2), and 77 obese subjects (BMI >30 kgm−2). There was a significant positive correlation between age and BMI ( p < 0.001). Self-report data was collected including history of diagnosis of diabetes, stroke, cancer, myocardial infarction, high blood pressure, high cholesterol, and total estimated physical activity per week. Education level was noted (those with or without degree-level qualifications) as well as gross household income (those above and below a threshold income of £30,000). Cognitive performance was measured and there were no incidences of Parkinson’s disease or multiple sclerosis.
When the data was analyzed, researchers found a nonlinear change in brain white-matter volume with age, increasing to a maximum in middle-age, and decreasing thereafter (Fig. 2p < 0.0001). When they compared models of white-matter volume between lean and overweight or obese subjects, they estimated an average increase in brain age of approximately 10 years for the overweight and obese individuals when compared to controls. At an age of 50 years, overweight or obese subjects had an estimated white-matter volume of 445 cm3 whereas the lean subjects reached the same volume at the average age of 60 years, equating to an average 10 years increased brain age for overweight or obese patients. Overall cortical surface area was negatively impacted by age in each group (lean controls, overweight, and obese). However, there was not a BMI-related difference in total cortical surface area and also there was not an age to BMI interaction.
Cognitive scores were available for 463 of the 473 individuals included in the analysis. The cognitive scores displayed a significant nonlinear decline with age and were independently predicted by brain size. However, there were no BMI or age to BMI effects between lean and overweight or obese individuals.
The results demonstrate that increased adiposity (adipose, or fat, content) has a significant impact on brain structure. The relationship between adiposity, white-matter volume, and age may be equivalent to an increase in brain age of up to 10 years in overweight and obese individuals. As the world’s population is increasing in prevalence of overweight and obese individuals, this relationship between adiposity and brain effects is concerning for the brain health of an increasing number of people across the globe.
- World Health Organization. Fact File: 10 Facts on Obesity. http://www.who.int/features/factfiles/obesity/facts/en/index1.html. Accessed September 1, 2106.
- Ronan L, Alexander-Bloch AF, Wagstyl K, et al. Obesity associated with increased brain-age from mid-life. Neurobiology of Aging. 2016; DOI: 10.1016/j.neurobiolaging.2016.07.010