The study found that a body mass index (BMI) of 30 or greater at age 50 years but not at 60 or 70 years was associated with an increased risk of dementia.
“Taken together, the present data demonstrate that the association between obesity and dementia is modified by age at obesity measurement, such that midlife obesity is a risk factor for dementia, but BMI begins to decline in those with dementia in the years before diagnosis,” Archana Singh-Manoux, Ph.D., of University College London and colleagues wrote.
For the study, 10,308 adults (33% women) aged 35 to 55 years in 1985, who were participants in the Whitehall II study, were followed up until 2015. (The Whitehall II study is an ongoing cohort study of men and women originally employed by the British civil service in London-based offices.) BMI was assessed six times, and 329 cases of dementia were recorded. Changes in BMI for more than 28 years before dementia diagnosis were compared with changes in BMI in those who did not develop dementia.
Researchers modeled the risk associated with obesity at ages 50, 60, and 70 years. To study the changes in BMI, they used repeat data and model trajectories of BMI for more than 28 years and a backward timescale anchored to the year of dementia diagnosis. The World Health Organization classification was used to categorize BMI as ≥30 (obese), 25 to 29 (overweight), and <18.5 (underweight).
A total of 10.9% of the participants in the trial were obese at age 50, 17.1% at age 60, and 18.7% at 70 years. BMI in those with dementia was higher at age 50 years but not different from those without dementia at age 60 and 70 years. “BMI is suitable for the assessment of risk of dementia and death,” Singh-Manoux and colleagues concluded.
“In the past 40 years there has been a startling increase in the number of obese persons, rising from 105 million in 1975 to 641 million in 2014,” they wrote. “Our results suggest midlife obesity is a risk factor for dementia, and the extent to which the continuing obesity epidemic will create a surge in future dementia rates is an important public health issue.”
For related information, see the Psychiatric News article “New Dementia Measures Address Disclosure of Diagnosis to Patients.”