Systematic review of consistency between adherence to cardiovascular or diabetes medication and health literacy in older adults.

OBJECTIVE: To review the relationship between health literacy and adherence to cardiovascular/diabetes medication. DATA SOURCES: We searched EMBASE (1974-February 2012) and MEDLINE (1948-February 2012). Search terms included health literacy, numeracy, health education and related terms, health literacy measurement tools, and medication adherence. STUDY SELECTION AND DATA EXTRACTION: English-language articles of all study designs were considered. Articles were included if they had a measurement of health literacy and medication adherence and if participants were older adults taking drugs for cardiovascular illness or diabetes mellitus. DATA SYNTHESIS: A total of 1310 citations were reviewed, including 9 articles that reported on 7 research studies. Most studies were retrospective, and all were based in the US. Because there was considerable diversity in measurements, participant characteristics, and outcome measures, we conducted a narrative synthesis rather than a meta-analysis. In assessing study validity, we looked at participant selection, method of measuring health literacy and medication adherence, missing data or losses, and adjustment for confounders. Of the 7 included studies, only 1 found a demonstrable association between health literacy and refill adherence. One clinical trial failed to show significant improvements in medication adherence after an intervention to improve health literacy.
CONCLUSIONS: The current evidence does not show a definite association between health literacy and medication adherence in older adults with cardiovascular disease or diabetes mellitus. In the absence of a definite link, efforts to develop interventions to improve health literacy would not necessarily improve adherence to cardiovascular medications. There is an urgent need for robust studies outside of the US, with wider, generalized recruitment of participants.