In the present population-based study, we evaluated the sex-related associations between body height and cognitive impairment among low-income elderly adults in rural China. We found that shorter body height was related to cognitive impairment independently of age, educational attainment, lifestyle factors, and health-related comorbid factors for elderly men, but not for elderly women. In a subgroup analysis, the association remained consistent among elderly men aged 60–64 years; each 1-dm increase in body height was associated with a 65% decrease in the prevalence of cognitive impairment.
Cardiovascular risk factors, including hypertension, diabetes mellitus, hyperlipidemia, and smoking, have been linked with cognitive decline in adults Childhood is a critical period for both brain and body development. Anthropometric measures, including head circumference and body height, are key indicators for brain and body development. A smaller head circumference was reported to be associated with poorer global cognitive performance and cognitive reserve [19, 20]. The Honolulu–Asia Aging Study suggested that height in middle life was a marker of childhood growth and was associated with dementia and cognitive impairment among elderly Japanese–American men living in Hawaii [7]. In a large Belarusian prospective birth cohort study, a taller height between birth and age 6.5 years was associated with higher cognitive scores at age 16 years, with a 2.5-point (95% CI 1.9, 3.0) per standard deviation increase [21]. Most studies in Western countries have suggested that height is associated with cognitive function in older age. A European study involving 11 countries reported that height was positively and significantly correlated with cognitive performance in later life, with each 10-cm increase in body height associated with a 0.04-standard deviation increase in a global cognitive score [8]. A cross-sectional study in a Portuguese community found that height was a good independent predictor of general cognitive function in later life, especially with respect to executive function and memory [9].
However, the relationships between body height in later life and cognitive impairment remain controversial in Asian countries. The Hallym Aging Study in Korea found sex-related associations between height and cognitive function. Among community-dwelling elderly men, compared with the tallest group, the shortest group had a 3.2-fold higher risk of cognitive impairment (OR 4.20; 95% CI 1.02–17.36), but this association was not present among elderly women [22]. A cross-sectional study from the Guangzhou Biobank Cohort suggested that body height was positively associated with cognitive function, but only in older men and younger women [13]. In addition, shorter sitting height and lower relative sitting height were found to be significantly associated with dementia among elderly women in the urban Shanghai community in China [14]. In the present study, body height had a positive association with cognitive function among low-income elderly men in rural China; however, no relationship was found for elderly women. Furthermore, another longitudinal Chinese study found that arm length was associated with cognitive impairment in men during a 3-year follow-up, but not in women [23].
Adult body height is the result of a combination of genetic and environmental factors [6]. Childhood environment, including nutrition and disease, accounts for 20% of variation in body height. Thus, body height is a good indicator of childhood living conditions. Early deficiencies in nutrition in childhood have adverse effects on physical growth and brain development, which in turn affect cognitive development [24]. Our findings suggest that shorter height and early-life nutritional deprivation may contribute to cognitive impairment among elderly men. A structural magnetic resonance imaging analysis performed in 515 middle-aged male twins revealed the mechanisms underlying this relationship: height was positively associated with total cortical surface area among male twins, which underlies the phenotypic height and general cognitive ability relationship [25]. Besides, male fetuses are more sensitive to disadvantageous prenatal conditions compared with girls in previous studies, which lead to lower birth weights and early life illness among men [26, 27]. Therefore, height might be a better indicator of early life conditions for men than women. Thus, there is still a need to elucidate the sex difference between body height and cognitive impairment.
Cardiovascular variables, including hypertension, diabetes, hyperlipidemia, and smoking, are risk factors for cognitive decline, while education is an independent protective factor against cognitive impairment and dementia in later life [28,29,30]. In a population-based study in a rural region of South Africa, short height in old age was associated with poor cognitive decline among those without a formal education but not among those with at least 8 years of formal education [31]. However, in the present study, we failed to find mediating effects of education on the height and general cognitive ability relationship. Consistent with our findings, height was significantly associated with cognitive function independent of education and other covariates in an English longitudinal survey of aging [32].
There are several limitations in this study. First, the study population was from a low-income, low-education, rural population in northern China, so its representation and generalizability are limited. Second, cognitive impairment was evaluated with MMSE scores; therefore, different types of cognitive impairment could not be further diagnosed in the study. Third, other confounding factors, including APOE4 genotype and diet, are important factors for cognitive decline, but they were not assessed in this study. Forth, low birth weight could be an important factor on cognitive and socioeconomic outcomes [33]. As all participants did not experience malnutrition at time of maternal pregnancy or the first years of life, birth weight or history of drought or famine was not included in present study. Finally, this was a cross-sectional study, so causal relationships between cognitive function and height could not be determined.