Body mass index and mild cognitive impairment among rural older adults in China: the moderating roles of gender and age

BACKGROUND: Evidence concerning the association between body mass index (BMI) and cognitive function among older people is inconsistent. This study aimed to investigate gender and age as moderators in association between BMI and mild cognitive impairment (MCI) among rural older adults. METHODS: Data were derived from the 2019 Health Service for Rural Elderly Families Survey in Shandong, China. In total, 3242 people aged 60 years and above were included in the analysis. Multilevel mixed-effects logistic regression was used to examine the moderating roles of gender and age, then further to explore the relationship between BMI and MCI. RESULTS: There were 601 (18.5%) participants with MCI. Compared with normal BMI group, low BMI group had a higher risk of MCI among older people [adjusted odds ratio (aOR) = 2.08, 95% confidence interval (CI): 1.26–3.44], women (aOR = 2.06, 95% CI: 1.35–3.12), or the older elderly aged ≥75 years old (aOR = 3.20, 95% CI: 1.34–7.45). This effect remained statistically significant among older women (aOR = 3.38, 95% CI: 1.69–6.73). Among older men, elevated BMI group had a higher risk of MCI (aOR = 2.32, 95% CI: 1.17–4.61) than normal BMI group. CONCLUSIONS: Gender and age moderated the association between BMI and MCI among Chinese rural older adults. Older women with low BMI were more likely to have MCI, but older men with elevated BMI were more likely to have MCI. These findings suggest rural community managers strengthen the health management by grouping the weight of older people to prevent the risk of dementia. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12888-021-03059-8.