Introduction

Cognitive health is defined as “the development and preservation of multidimensional cognitive structure that allows the older adult to maintain social connectedness, an ongoing sense of purpose, and the abilities to function independently, to permit functional recovery from illness or injury, and to cope with residual functional deficits” ¹ (p. 12). The maintenance of cognitive skills is one of the criteria used for the characterization of successful ageing and is associated with longevity, a satisfactory quality of life as well as physical and social wellbeing ².

The evidence indicates that older adults with normal cognitive performance maintain satisfactory degrees of autonomy ², independence ³ and community participation ⁴. Such individuals generally have higher levels of schooling and income ⁵ and are younger ³. Regarding lifestyle, older adults with no cognitive decline consume a moderate amount of alcohol ⁶, have broader social networks ⁷ and participate in activities involving mental, physical and social stimulation ⁸.

Most of the studies have focused either on the evaluation of factors related to the differences between individuals with cognitive decline and the ones considered to be normal ³ or the predictors of maintaining cognition function ^{4 , 8}. However, within the individuals with no cognitive decline the ones with above-average performances may have characteristics that make them a different group of interest for studying the cognition function, as these factors may assist in the establishment of prevention strategies aimed at preserving cognitive health among older individuals.

Thus considering the lack of evidence about the factors related to high performers with regard to cognitive function, the aim of the present study was to identify factors associated with above-average cognitive performance among older adults without cognitive decline in the city of São Paulo, Brazil.

Methods

A cross-sectional study was carried out using data collected in 2006 from the SABE study (Health, Well-Being and Ageing). The sample included survivors from the baseline study carried out in the year 2000 who participated in the second wave of the study in 2006 as well as the data on older adults from the second cohort started in 2006. All participants had no cognitive impairment and had complete information on the covariates needed for analysis. The sample was made up of 923 participants representing 730,051 community-dwelling older adults in the city of São Paulo. The SABE study is a multicenter survey launched in 2000 and carried out in seven countries in Latin America and the Caribbean. In Brazil, the sample size was calculated to represent the urban population aged 60 years and older living in the city of São Paulo. In 2006, the survey was continued in São Paulo and a new cohort was started, thereby transforming the SABE study into a multiple cohort study. Details on the sample size calculation have been published previously ⁹. All data were collected at the participants’ homes with the use of an interviewer-administered structured questionnaire addressing socioeconomic variables, general health and living conditions as well as a set of anthropometric measures.

The sample of the present study comprised 923 elderly individuals with no cognitive decline. The exclusion of individuals with cognitive decline was based on the score of the Mini Mental State Exam (MMSE) ¹⁰ using cutoff points based on level of schooling ¹¹.

Dependent variable

Cognitive performance was the dependent variable and categorized as “normal” or “above-average”. The above-average cognitive performance was determined based on scores equal to the highest tertile (no schooling: ≥ 24 points; 1 to 3 years of schooling: ≥ 26 points; 4 to 7 years of schooling: ≥ 29 points). The remaining scores were considered indicative of normal cognitive performance. Distribution in tertiles was not possible for individuals with 8+ years of schooling, as only three scores were possible for this group following the exclusion of individuals with cognitive deficit (28, 29 and 30 points) and 59.72% of the individuals had the maximum score (30 points). Thus, 30 points was considered indicative of above-average cognitive performance in this group and ≤ 29 points was considered indicative of normal performance. Figure 1 displays the sample selection process and distribution of participants based on cognitive performance.

Figure 1  Composition of sample. 

Results

The final sample was made up of 923 individuals, representing 730,051 community-dwelling older adults in the city of São Paulo. A total of 28.4% of the sample was classified as having above-average cognitive performance. Table 1 displays the distribution of the sample according to the independent variables. The vast majority belonged to the “60 to 74 year-old” age group and lived in multi-person home arrangements. 57.4% of the sample was made up of females. More than 70% reported being independent with regard to daily living activities.

The bivariate analysis revealed that individuals with above-average cognitive performance were younger (60 to 74 years of age), resided in multi-person home arrangements and had a conjugal partner. The prevalence of above-average cognitive performance was higher among males and individuals who reported having sufficient income to meet their daily needs. The group with above-average cognitive performance also had a lesser proportion of difficulties regarding BADLs and IADLs, maintained more contact with family and friends, managed their own finances and consumed a non-abusive amount of alcohol (Table 1).

Table 2 displays the results of the final multiple logistic regression model. Above-average cognitive performance was associated with two socio-demographic variables (age and self-rated sufficient income). Older adults with active social contact and those who consumed a non-abusive amount of alcohol had a significantly greater chance of having optimal performance and those with difficulty on IADLs had a 42% less chance of having optimal performance.

Figure 2 shows a lower likelihood of optimal performance with the increase in age. Maintaining alcohol intake and performance on IADLs constant (non-abusive alcohol intake and no difficulties on IADLs) and allowing for the progressive increase in age, individuals with social contacts and self-rated sufficient income (Model 1) had a greater likelihood of cognitive performance above-average than those with social contacts but insufficient income (Model 2) as well as those with a lack of social contact and insufficient income for basic expenses (Model 3). Maintaining all variables in the first model constant except self-rated income sufficiency, those at 60 years of age who reported insufficient income had an 8% lower likelihood of above-average cognitive performance in comparison with those with sufficient income (Model 2). The same comparison between the first model and the third model shows that those with insufficient income and a lack of social contact had about a 16% lower likelihood of above-average cognitive performance (Model 3).

Figure 2 Probabilities of above-average cognitive performance according to different ages. 

Discussion

The findings of the present study indicate that people with above-average cognitive performance are different to older individuals with normal performance: they tend to be younger and independent when it comes to more complex daily living activities. Moreover they have active social contacts and report on possessing an income that is sufficient for their basic expenses.

The differences in the methodologies used to evaluate cognitive performance and the lack of research studies evaluating individuals with a high level of cognitive performance make it difficult to compare studies. Concerning demographic and socioeconomic factors, a review of the literature reveals conflicting results regarding factors associated with cognitive performance. Some studies report that functional impairment is greater among older adults at a more advanced age ²³ and among those with a lower level of schooling ^{8 , 24}. In contrast to the findings of the present study, other authors have found no association between performance and gender ⁸. These differences between studies could be due to the methods applied to classify cognitive performance and to the analysis employed: a cross-sectional ²⁴ and longitudinal analysis focused on the evaluation of the maintenance of cognitive function ^{8 , 23}. The increase in age in the present study led to a significant reduction in the odds of exhibiting above-average cognitive performance, which is in agreement with findings described in previous studies ^{2 , 8 , 25}. The advance in age has been associated with a reduction in cognitive plasticity and brain reserves, diminishing the efficiency of global cognitive performance ²⁶. Moreover, self-rated sufficient income was an important predictor of above-average cognitive performance. Studies analyzing the relationship between income and cognition report that older adults with a higher income exhibit optimal performance at baseline and lower likelihood of a reduction in performance during follow-up evaluations ^{27 , 28}. Self-rated income sufficiency may be an indication of the efficient use of cognitive resources in the planning, evaluation and management of finances, which implies a better pattern of cognitive function ²⁹.

The only general health variable associated with the outcome was “difficulties with instrumental activities of daily living ”. This association may be related to the fact that older adults with a better functional performance have greater opportunities to be cognitively active. Analyzing older American women over a 15-year period, Barnes et al. ⁴ found a 40% chance of maintaining a satisfactory global cognitive performance among those who reported having no difficulties on IADLs. Pérez et al. ²⁹ found that those older adults without cognitive decline but with difficulties on IADLs at baseline had a greater chance of developing dementia over a ten-year follow-up period. Approximately half of the variance in the performance of activities of daily living is associated with cognitive performance ³⁰. Instrumental activities of daily living are those that require more sophisticated cognitive resources (memory, attention, quick reasoning, executive planning and functions, mobility, locomotion, interest, purpose and social interaction) ²⁹ and therefore constitute a good indicator of cognitive performance among seniors ³⁰. However, the direction of the association may be in the opposite way considering the cross-sectional design of the study. In this case people with lower cognitive performance would have more difficulty to perform more complex activities.

In the present investigation, the number of chronic health conditions and past living and health conditions were not associated with above-average cognitive performance. This is in contrast to findings described in previous studies ^{4 , 5 , 31}. The association between individual chronic diseases and above-average cognitive performance was also tested, but did not achieve statistical significance even in the bivariate analyses. In contrast, Barnes et al. ⁴ found that the maintenance of optimal performance was associated with the absence of diabetes and hypertension. Yaffe et al. ⁸ found a higher incidence of optimal performance among older adults without hypertension and diabetes in the bivariate analyses, but these associations lost their statistical significance after controlling for age and lifestyle. In a systematic review, some authors report that the association between chronic disease and cognition tends to be robust in studies in which the comparison group is made up of older adults with cognitive decline and dementia ⁵. Once again among the reasons for the lack of association could be the design of this study, as individuals with poorer health status with regard to chronic diseases may be lost to follow-up and therefore excluded in the present wave.

Regarding lifestyle, older adults who consumed a moderate amount of alcohol had greater odds of exhibiting above-average cognitive performance. However, there is no consensus in the literature on the benefits of alcohol intake with regard to cognitive performance, the adequate amount to produce such effects ^{6 , 20} or the most beneficial type of drink ³². According to Corley al. ⁶, the ingestion of small amounts of alcohol may be related to reductions in damage to white brain matter, subclinical cerebrovascular infarction and activity associated with fibrinogen as well as increases in high-density lipoprotein cholesterol and insulin sensitivity, all of which benefit the cardiovascular system and cognitive function in old age.

Conflicting findings are reported in the literature on the effects of social networks regarding the maintenance of cognitive performance. Some longitudinal studies have found that limited social contacts were associated with an increased risk of cognitive decline ³³, whereas other investigations have found no protective effect on cognition stemming from the size of one’s social network ³⁴, social ties and participation in groups ³⁵ or the size, frequency and composition of social networks ³⁶. Engagement in occupational and social activities has also been considered an indicator of above-average cognitive performance ^{8 , 24 , 37 , 38}. Older adults who remain socially active are thought to employ more cognitive resources, stimulate the potential for cerebral plasticity, benefit emotionally from interactions with others and have fewer depressive symptoms ^{7 , 39 , 40 , 41}.

According to Bosma et al. ⁴¹ and Salthouse ³⁸, the association between advanced activities of daily living and cognition may be reciprocal. The same could be observed in social relationships and in the engagement in productive activities. The non-engagement in such activities may be associated with lesser cognitive function, functional limitations, a lower income, depressive symptoms and a preclinical sign of decline in individuals classified as healthy in cognitive screening assessments ⁵.

There is evidence that older adults with broader social networks are more likely to exhibit optimal global cognitive performance ^{7 , 40 , 42}. However, the reported frequency of social contacts with family and friends was not associated with optimal performance in the present study, unlike the finding with regard to the existence of contacts. This suggests that the quality of social contacts may be more important than the quantity. Indeed, an individual can be surrounded by people, but not interact with them. This is especially true for individuals on the threshold of cognitive decline ³⁶.

Despite the importance of the data presented herein, the findings should be interpreted and generalized with caution, since the cross-sectional design does not make it possible to determine the direction of associations between above-average cognitive performance and the factors analyzed. Another limitation of the present study is related to the use of a screening test to evaluate cognitive performance, which does not imply that the individuals that were classified with a cognitive decline according to the cut-off points had a disease. Moreover, there are still divergences regarding the best cut-off points to be used in order to reduce the influence of education levels in the performance of the test. In this vein, individuals with low levels of education may have failed in the test in the absence of a disease and the ones with higher levels of education with mild levels of cognitive decline may have passed ⁴³.

The present findings confirm the notion that cognitive performance in old age is a multidetermined process and the result of different factors associated with lifestyle, living conditions and health. With the exception of the absence of chronic diseases, the present data are in agreement with the theoretical model of successful ageing proposed by Rowe & Kahn ⁴⁴, in which above-average cognitive performance is associated with the absence of disabilities and chronic diseases as well as greater engagement in life, as measured by participation in community and productive activities. The identification of factors associated with above-average cognitive performance can contribute substantially to successful ageing by allowing for the establishment of health promotion actions and prevention strategies aimed at cognitive decline.