Intrinsic capacity (IC) is defined as "all the physical and mental attributes possessed by the older person." This concept has gained momentum in recent years because it provides insights into the changes in the functional capacity of individuals during their life. Reserves and deficits in IC occur in different ways among older adults, making them difficult to study and address.
Introduction
The World Health Organization operationally defines intrinsic capacity (IC) as "all the physical and mental attributes possessed by the older person." This construct is based on a longitudinal pattern consistent with the continuous process of individual aging, which must be assessed through multiple observations over time rather than a single assessment. Recently, studies have analyzed the five IC domains (cognitive, locomotor, psychological, vitality, and sensory) and their relationship with sociodemographic and clinical conditions in older adults. In Latin American countries such as Mexico, all IC domains tend to decline with age, especially among women. While some clinical factors associated with IC decline have been identified separately in Mexico and Colombia, sociodemographic and familial determinants that may influence the decline in IC reserves have not been explored.
Study Design and Participants
This cross-sectional, correlational study included 348 community-dwelling older adults. Older community members were enrolled from Ciudad Madero, Tamaulipas (Mexico) and Manizales (Colombia). Participants from Mexico were recruited through the community clubs for older adult members of the "Adults in Action Programme." Participants from Colombia were recruited from the Primary Care Programs operating in the city's health centers. All participants were characterized by age >60 years and regular attendance of primary care programs. We determined a random sample by applying the formula for the estimation of averages with a known sampling frame, assuming a type I error of 0.05, precision of 0.03, and standard deviation of 0.3. Therefore, minimums of 280 and 297 individuals from Mexico and Colombia, respectively, were required.
Data Collection and Assessment
Sociodemographic, clinical, and family conditions were assessed as possible associated factors, and IC was analyzed across five domains: cognitive, locomotor, psychological, vitality (malnutrition through deficiency and excess), and sensory (visual and auditory).
We investigated sociodemographic characteristics including age, sex, marital status, and level of schooling. Clinical variables were identified by asking about the presence or absence of diseases with a predominance of cardiovascular, brain, and vascular diseases, as well as alcohol and tobacco consumption. Additionally, we assessed fall risk using the Downton scale. The number of steps walked per day was determined by providing pedometer and recording for 7 days, using the cut-off points proposed by Tudor-Locke as reference.
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We analyzed the five domains separately. Each domain was interpreted by considering the cutoff points established in the validated instruments and subsequently recoded as a dichotomous response to identify preservation or impairment in each domain as follows:
- Cognitive Domain: Assessed using the Pfeiffer questionnaire, in which some level of intellectual impairment was considered cognitive impairment and normal scores as preserved cognitive domain.
- Locomotion Domain: Assessed using the Tinetti Scale, with minimal and high risks defined as balance or gait impairment and no risk as preserved locomotor domain.
- Psychological Domain: Assessed using the Yesavage Scale, in which levels of mild and established depression were considered depressive symptoms, and the absence of symptoms was considered preserved psychological domain.
- Vitality Domain: Assessed using the Mini Nutritional Assessment (MNA) and anthropometric measurements (weight/height) were used to determine the body mass index (BMI; as the MNA does not identify overweight or obesity). After each result was obtained separately, two new variables were created to determine malnutrition deficiency and excess. The first was obtained by defining MNA scores <24 and BMI scores <27 kg/m2 as deficit malnutrition and the remaining scores as not having deficit malnutrition. The second variable defined MNA results >24 and BMI scores ≥27 kg/m2 as excess malnutrition, with the remaining scores defined as no excess malnutrition.
- Sensory Domain: Assessed by self-reporting the presence or absence of visual and auditory impairments.
Finally, the total IC was calculated by summing all the domains under a theoretical scale of 0-7 points (considering that two aspects were assessed in the sensory domain), where each impaired domain contributed one point (0 and 1 points for the preserved and impaired domains, respectively). Thus, the higher the score, the greater the IC impairment.
Ethical Considerations
This project was developed under the ethical and legal considerations for research in Mexico and Colombia. This proposal was approved by the ethics committees of the educational institutions of the authors (Colombia IRB No. 122/ 25 /06/2018, Mexico IRB No. 301.511-6/17-7700). We obtained informed consent from the participants and complied with bioethical principles (autonomy, beneficence, non-maleficence, and justice).
Statistical Analysis
Data were processed using IBM SPSS Statistics for Windows, version 24.0 (IBM, Armonk, NY, USA). Sociodemographic, clinical, and family characteristics were analyzed as frequencies, percentages, and measures of central tendency (for scale variables), and cross-tables were constructed by comparing the proportions for each country and applying the chi-square test. We proceeded in the same way for the characterization of the IC domains to identify the proportions of deterioration or conservation of each domain according to country. Finally, to identify the associated factors as possible predictors, we explored binary logistic regression models using the backward method and only the independent variables that were statistically significant in the bivariate analysis.
Results
For the whole sample, the age range was 60-92 years (average 70±6 years, median 69 years). Age discrimination by category showed statistically significant differences, with a higher proportion of older people in the 60-79-year age group in both countries. We also observed significant differences in the distributions by sex and level of education, with higher proportions of women and individuals with a low level of education (no education or primary education) in both countries. Marital status and occupation did not differ significantly between countries.
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Intrinsic Capacity Domains by Sex and Country
The IC domains showed no significant sex differences, except in the visual sensory domain, where self-reported visual impairment prevailed in 56.9% of women (p=0.016). We observed statistically significant differences for all domains according to country, except for the psychological domain. In older adults in Mexico, the three domains that reported the greatest deterioration were vitality (excess malnutrition, 59.3%), followed by the sensory (self-reported visual impairment, 57.5%) and locomotor (balance/gait impairment, 26%) domains. In Colombia, the main impaired domains were the locomotor (balance/gait impairment, 46.7%), sensory (self-reported visual impairment, 45.1%), and vitality (malnutrition due to excess, 32.0%) domains.
Factors Associated with Impairment in IC Domains and Total IC
Binary regression (for all participants) revealed factors associated with impairment in all domains and total IC. The locomotor domain had the highest number of associated factors, followed by excess malnutrition. Fall risk was the most frequent clinical condition associated with impairment in four of the eight models.
Cognitive Domain
A dysfunctional family environment was the main factor in the cognitive domain, which is consistent with recent findings in another study showing a lower prevalence of family functioning among groups of families with older people with mild cognitive impairment compared with their counterparts without cognitive impairment (59.3% vs. 89.7%). Family functionality implies coherence between the relationships of its members; individuation mechanisms that improve communication, knowledge, and growth of its members; and adaptation to changes in situations to guarantee security, independence, and greater autonomy.
Locomotor Domain
The locomotor domain showed the highest number of factors in this study. Among these factors, myocardial infarction demonstrated the greatest effect. Myocardial infarction has been reported as a cause of physical deterioration (especially in females) and presents as slower walking speed and frailty. Herein, the prevalence of myocardial infarction in the two countries was only 10.5%; however, 66.7% of these patients were females. We identified family functionality as the second factor, in which 16.4% of people living with dysfunctional family processes showed impairments in this domain. The third factor associated with locomotor impairment was age, in which 5.5% of people aged >80 years had impaired balance and gait. Another factor associated with the deterioration of this domain was related to dedicating oneself solely to household chores (vs. working or studying). In this case, the decrease in locomotion is explained by restricted mobility in the living space, with the consequent limitation of instrumental and social activities in the neighborhood and city in which the individual lives. However, herein, being single was associated with increased locomotor deterioration.
Psychological Domain
The main associated factor in the psychological domain was living in a dysfunctional family. Other studies have demonstrated a relationship between family functionality, the perception of health, and the presence of depressive symptoms in nonagenarians and centenarians. Our findings demonstrated a dysfunctional family environment was associated with a 6.7-fold increased likelihood of deterioration in the psychological domain in older adults, making this a significant finding.
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Vitality Domain
In the vitality domain, we observed a greater number of factors associated with excess malnutrition, including age (60-79 years), which is consistent with the findings of another study in South America reporting a higher risk of obesity in women in the same age group (odds ratio [OR]=1.88; 95% confidence interval [CI] 1.16-3.04). We observed a higher risk in the present study, (OR=4.1), which can be explained by the fact that the overweight and obese groups were analyzed together. Another factor related to deterioration in this domain was walking <7,499 steps/day, which, according to Tudor-Locke et al., corresponds to a group of people with basal or low physical activity, in whom the number of steps is not sufficient for weight control.
Sensory Domain
Factors such as being female and at a higher risk of falls were significantly related to impairment in the sensory domain. The causes of visual impairment (cataracts and corrected refractive errors) are associated with demographic transition; likewise, women aged ≥50 years show a higher prevalence of visual impairment. In the present study, 80% of older adults who reported having some type of visual impairment were females. Regarding the risk of falls, the relationship between visual and hearing impairments and postural control is well known.
Total Intrinsic Capacity
Finally, the results of the total IC revealed three factors, the most significant being a dysfunctional family environment. Family living conditions can be a protective factor that contributes to member support and well-being; however, problematic conditions are also associated with stress and health impairment. The results of the present study revealed that family dysfunctionality can lead to a 5.7-fold higher probability of IC deterioration in older individuals. These findings provide significant data to inform health interventions, particularly nursing interventions that aim to preserve the intrinsic reserves necessary for adaptation to the environment and performance of the maximum number of possible activities in daily life. Moreover, not having a partner decreased the total IC; thus, this condition can lead to unfavorable or disadvantageous situations over time, with the consequent loss of intrinsic and health reserves. Previous studies have reported higher relative mortality rates among divorced, widowed, and single individuals compared with married individuals. Additionally, the risk of falls increased the probability of the deterioration of total IC by 3.0-fold; however, this was the only geriatric syndrome that was considered a possible risk factor.