Association with Health Behaviors and Outcomes
Poor health literacy is only a problem if it leads to negative health outcomes. By now, the knowledge we have about health behaviors and outcomes associated with different levels of health literacy is quite extensive. An article by Berkman et al. (2011) provides a systematic review of this research. The review is a synthesis of 96 studies of good or fair quality, reported in 111 published articles: 98 focusing on health literacy and 22 on health numeracy. Studies typically measured health literacy via versions of REALM or TOFHLA, and numeracy via general math tests not specifically designed for the health-related context. The big picture created by the systematic review suggests that lower health literacy is associated with several poor outcomes. For a number of health conditions (asthma, congestive heart failure) and populations groups (elderly, inner-city patients), it is associated with higher rate of ER visits and hospital admissions, which suggests poorer disease management and more complications (Baker et al., 2004; Cho et al., 2008; Hope et al., 2004). Lower health literacy is also associated with underuse of important preventive services such as mammography screening and flu vaccination (Guerra et al., 2005; White et al., 2008). Individuals with lower health literacy also have more difficulty interpreting medications and nutritional labels and taking medications as directed (Davis et al., 2006; Kripalani et al., 2006). They also have more trouble interpreting health messages (Davis et al., 2006). Studies also suggest that, for the elderly, lower health literacy may be related to overall poorer health (Cho et al., 2008; Lee et al., 2009) and higher mortality (Baker et al., 2017; Baker et al., 2008; Sudore et al., 2006).
For a number of other outcomes (e.g., access to care, various specific health behaviors), the evidence of association with health literacy was deemed insufficient because of poor methodology of studies or inconsistent results. The relationship between numeracy and health outcomes was similarly judged as presently inconclusive because of insufficient or inconsistent findings. This means that there are some studies pointing at such associations, but it is too early to make a conclusive statement about it. As more research evidence is accumulated and methodology is refined, this evidence may emerge with stronger support.