Higher BMI Appears to Have Protective Effect Against Dementia in Patients With PD

A recent study examined the extent to which body mass index (BMI) at the time of a Parkinson disease (PD) diagnosis is associated with cognitive decline and the future development of dementia.

BMI alterations and body weight are thought to be associated with PD, the researchers said, although a clear link has not yet been established. Patients with PD were found to have a lower BMI than controls in a meta-analysis, while overweight and normal-weight individuals were more prevalent in the PD group in another cross-sectional study.

There have also been conflicting reports on whether patients with PD gain or lose weight in the years before and after their diagnosis. One study found that patients with PD lost weight several years before the diagnosis, while another study found no BMI changes a diagnosis, and another study observed weight gain during early PD.

In populations without cognitive difficulties, the association between BMI and cognitive function varies with age; a higher BMI in midlife is linked with a higher risk of dementia, whereas the association is reversed in late life. And in patients with other neurodegenerative conditions, mild cognitive impairment or Alzheimer disease, a lower BMI is associated with faster cognitive decline and a higher risk of developing dementia.

In this study, investigators sought to determine whether the BMI seen at the diagnosis in patients with de novo PD impacts the subsequent cognitive decline and the future development of dementia; they also examined the pattern of cognitive dysfunction in terms of the overall cognitive ability and the ability in each cognitive domain over 6 years of follow-up.

Researchers recruited 70 patients with PD who underwent neuropsychological testing every 3 years. They classified patients into the following 3 groups based on their BMI at the diagnosis: under-/normal weight (n = 21), overweight (n = 22), and obese (n = 27). They then evaluated differences in the rate of cognitive decline over time among the groups using linear mixed models and the conversion rate to dementia using survival analysis.

Obese patients with PD showed a slower deterioration of global cognitive function as well as language and memory functions than did the under-/normal-weight group during the 6-year follow-up.

The 3 BMI groups showed different rates of conversion to dementia (log-rank test: P = .026). The combined overweight and obese group showed a lower risk of developing dementia compared with the under-/normal-weight group (hazard ratio = 0.36, 95% CI=0.12—0.82, P = .046).

The study shows that a higher-than-normal BMI at the time of a PD diagnosis has a protective effect against cognitive decline and the conversion to dementia. PD patients whose BMI or weight decreased during follow-up showed a worse baseline cognition or a faster cognitive decline than those who maintained a stable BMI or weight.

Reference

Yoo HS, Chung SJ, Lee PH, Sohn YH, Kang SJ. The influence of body mass index at diagnosis on cognitive decline in Parkinson's disease [published online October 1, 2019]. J Clin Neurol. doi: 10.3988/jcn.2019.15.4.517.