Towards understanding the associations between health literacy and physical health

Low levels of health literacy—low “capacity to obtain, process and understand basic health information and services needed to make appropriate health decisions”—constitute a risk factor for poor health. For example, low health literacy is associated with a failure to adopt preventive and early detection strategies, limited knowledge of particular health issues, poor ability to perform specific health tasks and to adhere to medication plans and, most importantly, with numerous manifestations of poor physical health itself, including hospitalization rates and mortality. In order to lift the literacy-related barriers to health, it has been suggested to enhance people’s levels of health literacy and/or to adjust health-services to recipients’ literacy. For instance, interventions have been targeted at improving diabetes management or information access skills, and attention is being paid to simplifying patient-doctor communications and medical information given to patients. The success of these interventions has varied.
Whatever the strategy of responding to low health literacy, its effectiveness is likely to depend on how well the phenomenon itself, its antecedents and pathways to physical health are understood. For one, it is necessary to understand how health literacy is associated with other, better-established psychological and social constructs and whether these associations can help to explain why health literacy is related to health outcomes. Theoretical models of health literacy introduce general cognitive ability as one of its underpinnings, along with other factors such as educational and occupational influences. There is indeed some empirical evidence that scores on health literacy measures—which are in fact very similar to regular cognitive ability test—are related to broader cognitive differences among people. This is also consistent with the literature that shows associations between general cognitive ability and physical health. An obvious question that arises is to what degree general cognition accounts for the associations between health literacy and actual health outcomes. If it does so substantially, plans to raise heath standards by increasing health literacy can learn from the attempts to raise general cognitive ability. Likewise, prevention and health services should be adjusted to meet people’s skills in a broader set of areas, not just literacy (or numeracy) alone.
Alternatively, rather than being related directly to general cognitive ability per se, health literacy may stem from other correlates such as educational attainment or occupational level. This would, then, suggest that health literacy is a domain-specific set of skills and knowledge that is relatively independent of general cognitive ability and that people develop in response to life-course socioeconomic opportunities.
The present study investigated whether three popular operationalizations of health literacy were predictive of a sample of nine indicators of physical health in community-dwelling older people at age around 73 years. The unique feature of the participants, the Lothian Birth Cohort 1936, is that all participants had been administered a well-validated general intelligence test when they were about 11 years old. This made it possible to consider of the influence of general cognitive ability before people absorb most of the life-course influences on health literacy and health, and before adult ill health affects cognitive ability. We first tested the degree to which general cognitive ability, observed concurrently with the health literacy assessments in old age, could account for the health literacy associations with health outcomes. We then investigated the earlier life-course roots of the health literacy-health associations by testing to which extent the associations could occur due to shared influences from childhood cognitive ability, educational level and adult occupational social class.