INTRODUCTION

Cognition is the mental capacity of an individual to understand and solve everyday problems based on perception, language, reasoning, and sensory abilities (^{Moraes et al., 2010}). Conversely, cognitive decline (CD) is a decline in intellectual abilities, affecting key areas such as memory, language, learning, and the performance of everyday tasks and behavior (^{De Ronchi et al., 2005}; ^{Machado et al., 2011}). This condition has an impact in terms of reduced functional capacity, independence, and autonomy, affecting the quality of life and causing psychosocial damage (^{Machado et al., 2011}; ^{Pavel et al., 2023}).

CD derives from the normal process of aging or the transition to dementia, a chronic condition characterized by the presence of CD affecting a significant portion of the older population (^{Machado et al., 2011}; ^{Trindade et al., 2013}). As a result of the aging process, the number of individuals exposed to CD gradually increases, significantly impacting public health (^{Lira & Santos, 2012}; ^{Rosa et al., 2018}). The global prevalence of CD in community-dwelling older adults ranges from 5.1% to 41% (^{Pais et al., 2020}). In Brazil, however, this prevalence exceeds 50% in older adults treated in Primary Health Care (PHC) (^{Pereira et al., 2020}).

CD can manifest itself during aging and is proportional to advancing age, causing a decline in the structures responsible for the normal functioning of brain systems (^{De Ronchi et al., 2005}). In addition to age, other determinants of CD include educational attainment, sex, social support, lifestyle, and marital status (^{Wu et al., 2011}; ^{Pereira et al., 2020}; ^{Horacio et al., 2021}). Moreover, this situation can be exacerbated by food insecurity (FI), a condition that can be acute or chronic, and results from a lack of regular, sufficient access to food in terms of quantity and quality.

FI is a shortage of the food and nutrients (protein with high biological value, vitamins, minerals, and fiber) essential to maintaining health, which can lead to poor nutritional status and mental health (^{Martin et al., 2007}; ^{Frongillo et al., 2017}; ^{Koyanagi et al., 2019}). In addition, FI may lead to stress, which can trigger the onset of CD (^{Smith et al., 2021}). Food insecurity (FI) is believed to cause multisystemic physiological dysregulation (an increase in allostatic load), caused by nutrient deficit and chronic stress. The immune and metabolic systems are most severely affected, causing inflammatory and neuroendocrine damage that disrupts homeostasis and may impair cognition (^{Pak & Kim, 2021}; ^{Wilbrecht et al., 2024}). Conversely, an adequate diet is a protective factor for the preservation of cognitive functions, enhancing the ability to perform daily activities (^{Martin et al., 2007}).

Despite scientific evidence demonstrating the relationship between FI and CD, there is a dearth of studies analyzing this phenomenon across the levels of FI (mild, moderate, and severe). Moreover, as most research is conducted in high-income (developed) countries, it is essential to understand this situation in settings such as northeastern Brazil, where older adults have higher rates of FI due to vulnerabilities associated with low income and poor education, exacerbated by the shortage of social and health public policies (^{Geib et al., 2012}; ^{Royer et al., 2021}).

Given the rapid aging of the population and the lack of evidence on this issue in Latin America, it is necessary to determine the impact of FI, associated with inadequate, irregular dietary habits, on CD. This study therefore sought to understand the association between FI and CD in older adults treated in Primary Health Care in a municipality in the Northeast Region of Brazil.

METHOD

RESULTS

Of the 316 individuals assessed (11.2% losses), 61.7% were female, 54.4% were aged 60 to 69, and 51.9% were Black or people of color. It was also found that 72.8% of the older adults had had fewer than four years of schooling, 51.6% were partnered and 16.1% lived alone. Regarding their health status, 69.9% had been diagnosed with SAH and 34.2% were classified as underweight according to BMI. The prevalence of FI was 63.3% among older adults, with 25.6% experiencing moderate or severe FI. The prevalence of CD was 59.8% (Table 1).    

In the bivariate analysis, a statistically significant association was found between FI and CD (p = .026). In addition to FI, CD was also associated with schooling (p = .001) (Table 1). In the logistic regression analysis, after adjustments, a statistically significant association was only observed between households with older adults with moderate/severe FI and CD (OR 1.878; 95%CI 1.002 - 3.521). There was no association between mild FI and CD (OR 1.529; 95% CI 0.888 - 2.634). In the final model, in addition to FI, there was also a statistically significant association between CD and < 4 years of schooling (OR 2.454; 95% CI 1.445 - 4.167) (Table 2). The final model fit was observed through the value obtained in the Hosmer-Lemeshow test (p = .911) and Nagelkerke R square = .088.    

DISCUSSION AND CONCLUSION

This study found a statistically significant association between moderate/severe FI and CD in community-dwelling older adults treated in PHC in a municipality in the Northeast of Brazil. It was observed that households with older adults experiencing moderate/severe FI were almost twice as likely to have CD. In other words, more severe FI conditions, characterized by severe limitations on both the quantity and quality of the diet, may be associated with cognitive impairment in community-dwelling older adults.

A systematic review study by ^{Royer et al. (2021)}found that FI status is associated with a decline in cognitive function across the lifespan. A similar result was found in a study of older American adults showing an inverse association between FI and cognitive ability (^{Frith et al., 2018}). It is therefore possible to observe a strong relationship between FI and CD in older adults, as cognitive functions such as memory, language, attention, and mathematical problem-solving have been shown to be more impaired in older adults with FI. At the same time, older adults with FS may have a lower risk of CD. A longitudinal study conducted in India with a representative sample assessing various cognitive aspects found that older people with FS were less likely to have word recall problems or computational problems compared to those with FI (^{Kumar et al., 2021}).

This study found that only more severe cases of FI (moderate/severe) were associated with CD. Similar results were observed in a study conducted by ^{Koyanagi et al. (2019)} of adult and older adult South Africans, showing that FI, especially in its more severe forms (moderate and severe), is associated with cognitive impairment. Older people with moderate and severe FI were about four times more likely to have CD. A study of adult and older adult Puerto Ricans found an association between more severe levels of FI and lower cognition and a greater likelihood of CD, particularly among the older population (^{Gao et al., 2009}).

FI can contribute to the development of CD through a number of mechanisms, including inadequate food intake and poor diet quality. This is because, in the context of FI, the diet comprises fewer foods with higher nutritional value and greater consumption of ultra-processed foods, leading to nutrient deficiencies (^{Frongillo et al., 2017}; ^{Hutchinson & Tarasuk, 2021}). There is a decrease in the consumption of vegetables, fruits, and dairy products, as well as foods that are sources of vitamins A and B-6, calcium, magnesium and zinc (^{Hanson & Connor, 2014}). A study of older adults in Singapore showed that compromised nutritional status, such as malnutrition, is associated with CD, probably due to the lack of nutrients required for brain function and cognition (^{Chye et al., 2018}).

The literature contains evidence of this association between micronutrient deficiencies and CD (^{Mustafa et al., 2022}). Another study of community-dwelling older Brazilian adults found a strong association between CD and zinc deficiency (^{Marchetti et al., 2022}). An integrative literature review indicated that vitamin B12 and folic acid deficiencies are associated with the risk of CD in older adults, due to increases in the concentration of homocysteine and methylmalonic acid, which cause changes in the central nervous system and affect cognition (^{Sousa et al., 2020}). Conversely, an adequate diet, which is usually the case for older adults in a FS situation, consisting of foods such as fruits and vegetables, which are sources of antioxidant micronutrients and anti-inflammatory agents, has been shown to preserve cognition and therefore delay the onset  of CD (^{Gardener & Rainey-Smith, 2018}).

Older adults with FI, especially at moderate and severe levels, experience a decrease in the number of meals, the amount of food per meal and therefore a lower intake of macro- and micronutrients (^{Pereira et al., 2022}). In the study conducted by ^{Cardozo et al., (2020)}, families with moderate and severe FI were 55% and 57% respectively more likely to adhere to a  restricted diet, characterized by a lower frequency of consumption of most food groups, including fruits and vegetables. Moreover, families with  FI were 41% less likely to adopt healthy eating habits. If  a healthy diet is unattainable for those with FI, nutrient deficiencies that fail to protect cognitive function become more likely. This dietary scenario contributes to the development of CD in older adults.

In addition, the experience of FI can lead to mental health damage due to the stress caused by not knowing where their next meal is coming from, mainly due to low socioeconomic status (^{Pereira et al., 2023}). Studies have shown that the experience of FI can cause psychological distress and stress, which, in turn, can lead to changes in brain structures and functions, resulting in the onset or worsening of cognitive impairment (^{Vilela et al., 2014}; ^{Smith et al., 2021}). As observed  in a longitudinal analysis of adult and older adult Puerto Ricans, FI was significantly associated with higher cortisol levels, hypothalamic-pituitary-adrenal (HPA) axis dysregulation, and sympathetic nervous system markers (^{Gao et al., 2009}).

Repeated stressful situations due to FI increase allostatic load, which causes wear and tear to the body, leading to brain changes that culminate in CD (^{McClain et al., 2018}). The increase in cortisol levels due to stress may increase the desire for more palatable foods, such as foods with a high sugar and fat content, to reduce stress levels, acting as a reward system (^{Adam & Epel, 2007}). There may therefore be a greater tendency to make less healthy food choices as a result of the stress caused by FI. Dietary insufficiency associated with higher levels of FI and the negative effects of this stressful experience may exacerbate CD and the health of older adults with this status.

Despite the methodological rigor of this cross-sectional study, and the results showing an association between CD and FI, it is not possible to make statements about the causality between exposure and outcome. Longitudinal studies on this issue, which are as yet limited, would therefore be required to show the direction of causality between FI and CD. Another aspect to consider was the use of the MMSE, which, although it is the most widely used tool for measuring CD, lacks a standardized cut-off point. Nevertheless, reference values were chosen that were appropriate for the characteristics of the population. Furthermore, it was necessary to exclude older adults with a high degree of CD, since it was impossible to administer the MMSE correctly. Another limitation was the sample size, which probably influenced the power value of the study, calculated post hoc (67%). Although losses in the sample certainly contributed to this condition, they did not affect the representativeness of the sample, since the distribution of losses was not concentrated in specific strata.Moreover, nutritional covariates were not used in this study. This aspect can be considered a limitation in the adjustment of statistical models.

In terms of contributions, it should be noted that this is the first study to address this issue in older Brazilian adults. Another key aspect is the fact that the study focused on community-dwelling older adults treated in PHC. It is also worth noting that FI was analyzed in terms of its different levels, mild and moderate/severe, with the understanding that eating patterns and strategies differ in the various categories of this status.

This study showed that the experience of moderate/severe FI in households with older adults registered with PHC in Brazil may be associated with the presence of CD. In other words, unhealthy dietary patterns, with restricted quantity and quality of food and nutrients, can result in cognitive impairment in older adults. Nutritional deficiencies and mental health effects caused by stress and psychological distress may explain this association. In this respect, given the characteristics  of aging and their impact on the health of individuals, FI must be addressed with public policies that facilitate access to sufficient healthy food.