Greater exposure to clinical obesity during young adulthood is associated with a greater burden of white matter lesions in the brain in middle age, according to new research from the long-running Bogalusa Heart Study.
The researchers analysed data from 190 participants whom the study has followed from childhood into adulthood for more than 50 years. The participants underwent repeated assessments of their cardiometabolic health during young adulthood and middle age, followed later by brain MRI scans.
Rather than relying solely on body mass index, the scientists classified participants using the Lancet Commission's framework, which distinguishes preclinical obesity—excess fat without evidence of ongoing disease—from clinical obesity, in which excess fat is accompanied by impaired organ or tissue function or limitations in daily activities.
The findings showed that people with greater cumulative exposure to clinical obesity from young adulthood to middle age had more white matter hyperintensities by their mid-50s. These hyperintensities are areas of increased signal on MRI scans that may reflect small vessel disease and other forms of damage. No significant association was found between cumulative clinical obesity and the ratio of grey matter volume to total intracranial volume.
Dr Owen Carmichael, a professor of dementia research, explains that earlier studies of obesity and brain ageing produced mixed findings, with some even suggesting that greater obesity could be better for the brain. He says one reason for the confusion is that researchers had not clearly distinguished between people with excess body fat who had serious metabolic consequences and those who did not, and the Lancet Commission's framework seeks to address this problem.
The framework was developed by an international panel of experts that included three researchers from the Pennington Biomedical Research Center: Dr Eric Ravussin, Dr Philip Schauer and Dr John Kirwan. Dr Ravussin notes that the Commission sought to move the definition of obesity beyond body mass index towards a better understanding of how excess fat affects health and the function of tissues and organs.
The study is noteworthy because most previous research relied on body mass index measurements taken at a single point in time. Undergraduate student Christian Corsten, a co-author, stresses that metabolic health is not a snapshot and that the effects of metabolic disease can accumulate throughout life, with consequences for brain ageing.
The study was published in Neurology Open Access. The longitudinal design of the Bogalusa Heart Study, which began in 1972, allowed the researchers to examine cumulative exposure to clinical obesity over decades, something that is difficult to capture in short-term studies.
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