Background: Emerging evidence suggests the relationship between health literacy and health outcomes could be explained by cognitive abilities.
Objective: To investigate to what degree cognitive skills explain associations between health literacy, performance on common health tasks, and functional health status.
Design: Two face-to-face, structured interviews spaced a week apart with three health literacy assessments and a comprehensive cognitive battery measuring 'fluid' abilities necessary to learn and apply new information, and 'crystallized' abilities such as background knowledge.
Setting: An academic general internal medicine practice and three federally qualified health centers in Chicago, Illinois.
Patients: Eight hundred and eighty-two English-speaking adults ages 55 to 74.
Measurements: Health literacy was measured using the Rapid Estimate of Adult Literacy in Medicine (REALM), Test of Functional Health Literacy in Adults (TOFHLA), and Newest Vital Sign (NVS). Performance on common health tasks were globally assessed and categorized as 1) comprehending print information, 2) recalling spoken information, 3) recalling multimedia information, 4) dosing and organizing medication, and 5) healthcare problem-solving.
Results: Health literacy measures were strongly correlated with fluid and crystallized cognitive abilities (range: r=0.57 to 0.77, all p<0.001). Lower health literacy and weaker fluid and crystallized abilities were associated with poorer performance on healthcare tasks. In multivariable analyses, the association between health literacy and task performance was substantially reduced once fluid and crystallized cognitive abilities were entered into models (without cognitive abilities: β= -28.9, 95 % Confidence Interval (CI) -31.4 to -26.4, p; with cognitive abilities: β= -8.5, 95 % CI -10.9 to -6.0).
Limitations: Cross-sectional analyses, English-speaking, older adults only.
Conclusions: The most common measures used in health literacy studies are detecting individual differences in cognitive abilities, which may predict one's capacity to engage in self-care and achieve desirable health outcomes. Future interventions should respond to all of the cognitive demands patients face in managing health, beyond reading and numeracy.