Association of body mass index and dietary intake with mild cognitive impairment and dementia: a retrospective cohort study

BACKGROUND: The prevalence of cognitive impairment in older adults is gradually increasing, and this is leading to many adverse outcomes. Common causes of cognitive impairment in advancing age are mild cognitive impairment (MCI) and dementia. However, how the nutritional status and nutrient intake are related to MCI and dementia is controversial. Therefore, we aimed to evaluate the association of body mass index (BMI) and dietary intake with the risk of MCI and dementia. METHODS: This retrospective cohort study involved 821 participants aged ≥ 50 years from a previous population-based cohort study: the Electricity Generating Authority of Thailand (EGAT) study in 2013–2014 (baseline) and 2018–2019 (follow-up). Dietary intake was recorded using a 12-month self-reported food frequency questionnaire. MCI and dementia were diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria using the Montreal Cognitive Assessment with ADL and the Kessler Psychological Distress Scale (K10) at study entry and at the 5-year follow-up. RESULTS: Among the 821 participants, the mean age was 60.0 ± 4.3 years, and the incidence rate of MCI and dementia was 42.5 and 11.2 per 1,000 person-years, respectively. The rate of MCI and dementia was higher in participants aged ≥ 60 years and with an education level of < 7 years. The rate of MCI was also higher in those with a BMI of ≥ 25 kg/m(2) and type 2 diabetes. Compared to BMI 18.5–22.9 kg/m(2), BMI of ≥ 25 kg/m(2) (odds ratio 1.91 [95% confidence interval, 1.12–3.26], p < 0.001) was associated with an increased risk of MCI after adjusted for age, education level, and type 2 diabetes. Regarding dietary intake, fresh red meat consumption was inversely associated with the risk of MCI (p = 0.037) and dementia (p = 0.011) after adjusting for age, education level, type 2 diabetes, and BMI. CONCLUSION: Obesity was associated with a greater risk of MCI. Moreover, low consumption of fresh red meat could be a risk factor for MCI and dementia. Further studies are required to confirm and explain these findings. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12877-022-03700-5.