**1. Introduction**

Health literacy (HL) is an individual's ability to gain, understand, process, and apply health information to make appropriate health decisions [1]. Health literacy has been found imperative for improved individual health. Many studies have shown a positive relationship between HL and health knowledge, such as knowledge of the negative effects of smoking and drinking and how to control chronic diseases such as HIV and hypertension [2]. Low HL, conversely, is associated with poor health, limited use of preventative care, and higher hospitalization rates [3]. Moreover, a recent literature review found that low HL is linked to low medication compliance and misunderstanding medical information, which helps explain findings linking low HL to decreased health among certain at-risk populations [4]. Unfortunately, the majority of HL measures, interventions, and research has been focused in the United States among primarily White populations [1,5,6]. Global HL research is essential more now than ever given the recognition, attention, and resources being dedicated to addressing health disparities throughout the world on an individual, community, and societal level [7–9]. A global effort to understanding HL is necessary when seeking to address the needs of migrant populations—particularly the growing migration networks connecting the U.S., Mexico, and Central America [8].

A focus on HL in Mexico is of particular importance at this time due to the country's recent implementation of universal healthcare [10]. Through a series of nationwide health reforms and financial restructuring between 2003 and 2012, universal healthcare in Mexico, known as Seguro Popular, is now utilized by over 60 million Mexican citizens. Prior to the beginning of reforms in 2003, the Mexican healthcare system was decentralized, and it fell on specific states to provide healthcare to the uninsured population. Often this meant high out-of-packet expenses for low-quality care, while insured Mexican citizens received healthcare from well-funded federal hospitals and clinics. This created inequalities in health services between the insured and uninsured. The goals of the healthcare reforms were to offer the equivalent of the federal health services to the uninsured population, reduce out-of-pocket-expenses, and take some of the financial responsibilities off the states. There were a large number of changes under the healthcare reform (for a full overview of the policy and further statistics, see Knaul et al. [11]); the current system (Seguro Popular) now works as a public fund under the Ministry of Health that the government, the states, and individual citizens (based off income, with lower-income families exempt) all pay into. The fund covers essential healthcare services of enrolled citizens who do not have health insurance through employment, creating an option of health coverage for all Mexican citizens [11]. While citizens have the choice of whether or not to enroll, many states have elected to automatically enroll all their citizens as governmen<sup>t</sup> funding for healthcare distributed to each state is based on enrollment numbers [11]. Since the implementation of Seguro Popular, use of health services by Mexican citizens of all ages has steadily increased [12], and the dramatic improvements in healthcare coverage and service delivery have been heralded by health watchdogs and governments throughout the world [13]. However, several limitations of healthcare access in Mexico still persist, especially in isolated rural areas where there are a lack of clinics, doctors, and relatively low patient–provider ratios [13–15]. Furthermore, vulnerable groups in Mexico such as women, the elderly, and low-income populations are still facing insurance gaps, and preventative care practices are not available for large portions of the population [16], as any services not deemed "essential" by the governmen<sup>t</sup> are not covered under Seguro Popular [11].

Unfortunately, an improved health system does not necessarily lead to improved HL among consumers. In fact, a changing healthcare system could make navigating services more difficult for individuals [17], particularly those with low HL. For example, Gazmararian et al. [18] found that among those with access to universal healthcare in the U.S. (i.e., Medicare for the elderly), 23.5% of English-speakers and 34.2% of Spanish-speakers still had inadequate HL. Furthermore, citing statistics from a Kaiser Permanente survey, Levitt [19] discussed the implications of the Affordable Care Act (ACA) on newly enrolled Americans. Only 57% of the surveyed population understood the term "provider network" and only 53% could define "a deductible", demonstrating the challenges facing new consumers trying to find their way within a complex health bureaucracy. Since individuals with limited HL inherently struggle to obtain care and make informed health decisions, assessing the HL of healthcare recipients should be a priority whenever there is a major shift in the structure of a national healthcare system. Unfortunately, at the time of this literature review, to our knowledge only one study has assessed HL in Mexico after the full implementation of Seguro Popular. Verastegui, De La Garza, and Allende-Perez [20] surveyed adults in an outpatient Mexican cancer clinic and found low HL in 15.4% of their sample, suggesting the vast majority had at least adequate HL. While their study provides important information for a unique subset of the population (adult patients with cancer), HL research is nonexistent among the majority of the Mexican population, including groups with historically low HL, such as youth [21].

An understanding of HL among youth is important because adolescence is a key development stage where children foster skills for adulthood [22]. Research suggests that low HL in youth—which can lead to the misinterpretation or misuse of health information—is correlated with adolescent obesity [23], less positive health habits [17], and an increase in risky behaviors, such as unsafe sex [24]. In developing nations, it is particularly important for youth to be able to discern between correct and erroneous health information as they typically have less access to the internet, fewer health professionals in their communities, and poorer health outcomes compared to youth in more developed regions of the world [25]. Although a few studies on adolescent HL have been conducted outside the US, the majority of HL studies among adolescents have focused on children in the U.S. [26].

One of the few studies that collected data outside of the U.S. was conducted by Hoffman and Marsiglia [25]. Using a sample of 230 adolescents, they explored the link between HL and substance use among youth in Guatemala. They found that those who went through a substance abuse prevention program scored higher on HL assessments than those who did not. Their results sugges<sup>t</sup> that in more rural, developing parts of the world, utilizing existing health promotion programs and resources could be a viable, and economically beneficial, way to target and improve HL. Another global study offered a preliminary look at adolescent HL in Taiwan [27]. In her sample of over 1600 Taiwanese high school students, Chang found that adolescents with lower HL also had lower health status and poor health behaviors. Studies such as these are important foundational efforts, and similar efforts—within the context of critical HL—are needed in countries such as Mexico where information about the impact of healthcare changes is crucial for identifying systematic strengths and shortcomings in their new system.

In response to the growing recognition of the value of studying adolescent HL, frameworks with attention to adolescents specifically have been developed [6,28]. One such framework was developed by Massey, Prelip, Calimlim, Quiter, and Glik [29], who conducted 12 focus groups with 137 publicly insured teenage youth in the U.S., and completed 36 key informant interviews with primary care physicians. The authors' goals were first, to clearly operationalize the growing definition of adolescent HL, which had lacked a clear and succinct definition in the literature [22], and second, to develop a framework that can be used to develop specific measures and scales of adolescent HL. They identified five prominent domains, each of which serves to operationalize an adolescent's knowledge, attitudes, and practices in a healthcare setting: (1) their ability to appropriately navigate the health system (e.g., knowing how to make an appointment); (2) their knowledge and implementation of their own rights and responsibilities; (3) their knowledge of the need for and the implementation of preventative care practices; (4) their demonstration of appropriate and accurate health information seeking practices; and (5) their ability to form positive and effective patient–provider relationships. Competence in each of these domains can help to define the extent to which an adolescent is "health-literate", as utilizing an operationalization of adolescent HL with multiple domains can better capture the varying definitions of HL [29]. With this expanded framework, policy makers and stakeholders may be able to better identify where gaps in services exist.

This model in particular serves as a useful lens for analyzing adolescent HL as it focuses on many aspects of critical HL, specifically on how adolescents actually interact with health systems. This is becoming more imperative as more and more adolescents gain access with the expansion of universal healthcare worldwide [29]. Critical HL differs from other aspects of HL (e.g., document, quantitative, and functional HL) in that it centers on the ability of an individual to apply their health knowledge in a manner that allows them to exert control over their health [30–32]. Chinn [31] defines three unique aspects to critical HL: information analysis and appraisal, social/structural aspects of health, and collective action. While HL addresses an individual's ability to obtain health knowledge through reading, listening, or searching out information, critical HL is application and action-focused, and thus is a more robust framework for assessing the HL of populations or groups as it points to the ability to actually use information to improve one's health [33]. Within Massey et al.'s [29] model for adolescent HL, there is an underlying focus on actions adolescents can take to gain control over their health; specifically, asking questions of their doctors, taking appropriate steps to access their healthcare, and making preventative health decisions, which may ultimately improve their health. This focus on action also incorporates the growing efficacy and control adolescents have over their healthcare [22]. Massey et al.'s model [29] may also serve as a guide for cross-cultural research because it focuses on actual health behaviors, which allows for more attention to variation across cultures, versus solely health knowledge of adolescents, which many times is measured through comprehension only [22]

and, subsequently, with stakeholders in policy considerations aimed narrowly at increasing adolescent knowledge. Considering the changing landscape of healthcare in Mexico, use of Massey et al.'s framework, which specifically focuses on interaction with the health system, may be able to provide valuable insights concerning the assessment, promotion, and actions taken by adolescents with regard to HL. Therefore, the purpose of this study was to assess the fit of Massey et al.'s framework of critical HL among Mexican youth by exploring their experiences utilizing healthcare services at a community health center. In doing so, we recognize the inherent limitations of applying a US derived model to Mexican youth, namely that the US and Mexico have very different health systems and distinctive norms and expectations surrounding healthcare utilization. Rather than comparing findings across cultures, we focus on the extent to which Massey et al.'s model fits, which may provide a useful framework for understanding Mexican youth experiences in their own right. Expanding our understanding of adolescent HL and health-seeking behaviors in Mexico is a foundational step towards understanding the potential impact of a changing healthcare system on their ability to meet their personal health goals.
