The role of health literacy in diabetic foot disease : simple communication is no mean feet!

Aims Diabetic Foot Disease is a devastating complication of diabetes and places a significant burden on individuals and healthcare systems alike. Whilst people with diabetes have low health literacy, which is associated with poorer health outcomes in diabetes, its role in diabetic foot disease and its prevention, is unclear. This thesis aims to identify, and subsequently address gaps in knowledge of the role of health literacy in diabetic foot disease. Methods This thesis comprises a systematic review and meta-analysis and The Southern Tasmanian Health Literacy and Foot Ulcer Development in Diabetes Mellitus (SHELLED) study, a prospective study of 222 participants with diabetes recruited from a single tertiary hospital outpatient clinic. The aim of the systematic review was to investigate associations between health literacy and diabetic foot disease and its risk factors of peripheral neuropathy, peripheral artery disease and foot deformity. Databases of PubMed, EMBASE, CINAHL, Web of Science, Scopus and Science Direct were searched and studies in English with valid and reliable measures of health literacy and published tests of association were included. Data on associations between diabetic foot disease and its risk factors as well as foot care, were extracted. Where appropriate, meta-analyses were performed using random effects models. Recruitment for SHELLED was conducted between 2015 and 2016, with four years of follow up thereafter. Participants with Type 1 or Type 2 diabetes aged >40 years without a history of foot disease, psychotic disorders or dementia were recruited. Baseline measures of peripheral neuropathy, peripheral artery disease and foot deformity were conducted by a podiatrist according to published guidelines. Health literacy was measured in two ways ‚ÄövÑv¨ functional health literacy using the short form Test of Functional Health Literacy in Adults (S-TOFHLA) and nine domains of health literacy by the Health Literacy Questionnaire (HLQ). Covariates measured at baseline included demographic characteristics, cognition, psychological measures and foot care behaviors. Participants were followed up annually via telephone to enquire if they had developed an index foot ulcer, defined as a non-healing wound for >2 weeks below the ankle, during the preceding 12 months. This was confirmed by the participants‚ÄövÑv¥ general practitioner or from hospital medical records. Three sets of analyses were performed using logistic and linear regression as appropriate. The first analysis was of baseline associations of health literacy with individual risk factors for, and combined overall risk for foot ulcer development were assessed using logistic regression. The second investigated associations of demographic variables with health literacy measures from baseline data. The final analysis examined associations of health literacy with index foot ulcer development at 4 years. Results Sixteen articles were included in the systematic review, with 11 in the meta-analysis. The strongest evidence was of there being no association between health literacy and foot care (7 studies, 1033 participants, correlation coefficient 0.01 (95% CI -0.07, 0.10). There was no statistically significant difference in health literacy levels between people with and without peripheral neuropathy (2 studies, 399 participants, standardized mean difference -0.14 (95% CI -0.47, 0.18). People with inadequate health literacy had twice the odds of diabetic foot disease compared to those with adequate health literacy, which although not statistically significant, may be clinically important (2 studies, 1278 participants, OR 1.99, 95% CI 0.83, 4.78). In the SHELLED study, participants were predominantly (58.6%) male with a mean duration of diabetes of 18 years, with 77.9% insulin-dependent. 88 (39.6%) participants had mild cognitive impairment. 127 (57.2%), 81 (36.5%) and 14 (6.3%) of participants had zero, one and more than one risk factors for foot disease respectively. In the first analysis, higher S-TOFHLA scores were associated with lower risk for foot disease (OR 0.96, 95% CI 0.93, 0.99) and loss of protective sensation (OR 0.95, 95% CI 0.91, 0.995) in univariable but not multivariable analyses. There were no other clinically important or statistically significant associations between health literacy and peripheral artery disease, foot deformity or overall risk of foot disease. In the second analysis, variables significantly associated with poorer functional health literacy in multivariable analysis were poorer cognition (OR 0.71, 95% CI 0.63, 0.79) and greater educational attainment (OR 0.88, 95% CI 0.76, 0.99). Age was negatively associated with two HLQ domains (appraisal of health information and ability to find good health information) (both beta =-0.01). Educational attainment was positively associated with four domains (having sufficient information to manage my health, actively managing my health, appraisal of and ability to find good health information) (beta ranging from +0.03 to 0.04). Diabetes distress was negatively associated with five domains (having sufficient information to manage my health, social support for health, ability to actively engage with healthcare providers, navigating the healthcare system and ability to find good health information) (beta ranging from -0.14 to -0.18). At the end of four years, 191 (86.0%) participants completed the study, with 31 (13.9%) lost to follow-up. 178 (80.1%) were ulcer free and 13 (5.9%) had developed an incident ulcer. In multivariable analyses, better functional health literacy scores were protective against foot ulcer development (S-TOFHLA OR 0.94, 95% CI 0.88, 0.99). Better scores on two HLQ domains reduced the odds of foot ulcer (actively managing my health (OR 0.23, 95% CI 0.08 to 0.65) and understanding health information well enough to know what to do (OR 0.39, 95% CI 0.19 to 0.78). After adjustment for MOCA scores, the protective effect of better overall health literacy persisted but not functional health literacy. Better cognition scores also reduced the risk for incident foot ulcer development by as much as 23% (OR 0.77, 95% CI 0.63, 0.94). This was independent of baseline category of risk for foot disease. Conclusions The strongest evidence from this thesis is that both functional and overall health literacy, as well as cognition, are significantly associated with development of an index foot ulcer. This is despite the lack of significant associations identified in the systematic review and meta-analysis, and the cross-sectional component of the SHELLED study. People with these deficits should be identified and their health literacy and cognitive needs accommodated in health policy and communication to improve diabetic foot disease prevention