Height is representative of childhood health and nutrition, which affects the development of intelligence [1]. Childhood height is a strong predictor of cognitive function [2]. Likewise, if their health and nutritional status are good, adolescents are taller and have better cognitive abilities [3]. Fetal and early childhood nutritional status are also associated with the incidence of chronic disease in midlife [4]. Such disease can result in brain damage and thus in cognitive decline [5]. In one Finnish study of the school health examinations of males aged 6 and above, those who grew rapidly within a single year had a lower risk of coronary heart disease [4]. In the Nurses' Health Study [6], taller women had a lower risk of coronary heart disease. In some studies, greater height has been associated with reduced mortality [7,8], while in another study, short stature was associated with a lower rate of chronic disease and longer life expectancy [9]. In a study of elderly men (aged 76-95 years), it was suggested the onset of dementia could be postponed or prevented by maximizing growth of the body through improving childhood living conditions and adolescent nutrition [10], while in another study, taller elderly individuals had better cognitive functioning [1]. In the Health and Retirement Study, which was initiated to examine the physical and mental health, quality of life, and living environment in the population aged 50 and above since 1992, height was associated with various important health outcomes after 50 years of age in a follow-up study. In addition, taller elderly individuals had better cognitive functioning [1]. Likewise, height reflects childhood living conditions and is an important factor for healthy senescence.

There are only few domestic studies on the relationship between height and cognitive function. The study by Kim et al. [11] in women aged 60 and above is representative. One of the other studies is on the relationship between the lengths of extremities and dementia in an elderly population aged 65 and above [12], while another one is investigated the association between the length of the upper limbs and cognitive function [13].

Therefore, given the paucity of research in this area, this study investigated the relationship between height and cognitive function in a senior population residing in Chuncheon.

In the males, more educated subjects tended to be in the normal group compared to uneducated subjects. Uneducated subjects of the female group were more distributed in the cognitive impairment group, and educated subjects were in the normal group. The cognitive impairment group in males was much more likely to contain subjects with a current smoking status. The average height in the males was 159.4 cm in the cognitive impairment group and 162.9 cm in the normal group. For the females, the average height was 146.8 cm in the cognitive impairment group and 149.4 cm in the normal group. These results were statistically significant (p<0.001). Height was divided into quartile ranges (Q1-Q4) by sex. In the males, the shortest group was highly distributed, with 46.5% in the cognitive impairment group, followed in sequence by Q2 (=Q3) and Q4. In the cognitively normal group, individuals were evently distributed by height. In the females, as in the males, there were an increasing number of subjects in the cognitive impairment group as height decreased. The proportion of normal subject in the shortest group, on the other hand, was 17.7%, while that of normal subjects in the tallest group was 29.2%. This meant that taller subjects tended to be in the normal group (Table 1).

Cognitive function scores in each height quartile range were divided by sex. In both sexes, greater height was associated with higher cognitive scores, and this was statistically significant under the significance level of 0.05 (Figures 2 and 3).

A logistic regression analysis was performed to investigate the relationship between cognitive function and height. After correction for age, education, and smoking factors, the risk of cognitive impairment was 4.20 times higher in the shortest group (Q1) than in the tallest group (Q4) of the males (95% confidence interval [CI]=1.02-17.36) (Table 2). In the females, the risk of cognitive impairment was 4.29 times higher in the shortest group than in the tallest group (95% CI=2.07-8.92); however, there was no relationship after correction for age and education factors (OR, 1.65; 95% CI, 0.62-4.40) (Table 2). Because short height and cognitive function may be affected by medical history, the data was analyzed with stratification by diseases; however, there was no significant difference in the results before and after stratification (data not shown).

In this study, a relationship between height and cognitive impairment was shown in the males with correction for age and educational factors; but there was no relationship in the females. In various recent studies, height has been shown to be an indicator of childhood living environment, and childhood health condition strongly affects health in adulthood and senescence [16].

Reviewing previous studies on the relationship between height and cognitive function, it was reported that height was associated with Alzheimer's disease and vascular dementia in a cohort study of Israeli males [10]. Another British birth cohort study [17] has suggested that height in all ages showed a positive relationship with cognitive function in 3,000 people. In a study of Japanese males who moved to the US, short height in early life indicated a stronger potential for cognitive impairment [18]. In addition, it was reported that height had a positive association with cognitive impairment in Korean females [11]. In most studies, it has been suggested that height has a relationship with cognitive function; however, no relationship was shown for the females in this study. Mak et al. [19] suggested that the length of the lower extremities had no association with cognitive function in 290 males and females aged 55-75 grouped by three-year intervals in a follow-up study. Furthermore, in the study of Jeong et al. [13] on 235 males and females aged 65 and above residing in Namwon City, South Korea, although there was no association with cognitive impairment, the length of the arms showed a relationship with cognitive impairment; thus, it was suggested that the length of the arms was a more stable predictor of cognitive function.

Childhood living environment and cognitive development level affect educational attainment, school achievement, and eventual choice of occupation [1]. Some part of the reason that the childhood living environment affected cognitive function in senescence may be that children with high socioeconomic status had a high education level [1]. The males in the generation that is currently elderly had a greater opportunity to be educated than the females of the same cohort. The difference by sex could be explained by the complex effects of education and social roles rather than by sex itself [20]. With a life course perspective, women have fewer chances to obtain social positions, opportunities, and resources during their whole life course, and this result accumulated [21]. Likewise, the difference in cognitive function by sex is caused by the different opportunities for education, and thus there was no relationship between height and cognitive function with the correction for educational factors in the females.

The genetic factor contributes only 20% to height, and the effect of the genetic factor is decreased by poor environment [22]. Poor childhood health and nutrition affect physical health in adulthood, and thus cognitive function. Furthermore, these conditions cause diabetes mellitus, hypertension, and cardiovascular diseases, which are related to cognitive impairment of the elderly [23]. At the same time, a cohort study of twins suggested that height had a strong association with a genetic factor as well as childhood environmental factors [24]. Moreover, in a Danish cohort study [25], it was reported that the relationship between height and cognitive function decreased in developed social environments after the Second World War. As Korean socioeconomic conditions have continued to develop rapidly, ongoing studies on the relationship between height and cognitive function are needed.

It is difficult to explain the direction of cause and effect between height and cognitive function with this study because it is a cross-sectional study. Because cognitive function is affected by various factors and changes over time, it can be concluded that a cohort study to investigate cognitive function and the factors affecting it would be more effective than a cross-sectional study.

This study was performed to examine the relationship between height and cognitive function in the elderly population aged 65 and above residing in Chuncheon City, South Korea. In the males and the females, taller elderly individuals had a better average cognitive functioning score. With the logistic regression analysis, the risk of cognitive impairment in the shortest group was higher than in the tallest group for the male, while, no relationship was shown in the female.