This study showed that intensive interventions tailored to the needs of low-income Latinos can result in clinically important short-term improvements in glucose control and glucose variability. However, strategies to sustain these improvements are needed. The clinical significance of the impact of this intervention is considerable in light of the UK Prospective Diabetes Study (UKPDS) data showing that, for every percentage point decrease in HbA1c
, there was a 35% reduction in risk of diabetes complications (22
). Furthermore, there appears to be no sharp threshold for the clinical importance of reducing HbA1c
level, which even at levels associated with insulin resistance but not clinical diabetes is still a marker for increased risk of cardiovascular disease (23
This theory-based intervention targeting patients’ diabetes knowledge, self-efficacy, and self-management behaviors was successful in producing significant improvements in all three targets areas. Furthermore, these improvements were significantly associated with HbA1c
at 12 months, showing that the theoretical constructs mediated the effect between the intervention and HbA1c
. Improvements in knowledge and self-efficacy suggest that literacy-sensitive materials and strategies can bring about important and needed changes. Likewise, the focus on skills building through hands-on activities may have facilitated the development of self-efficacy and behavioral skills needed to implement the newly acquired knowledge. Of particular interest were the dietary change findings and their mediating role in the observed improvement in glycemic control. The maintenance of dietary changes at the 12-month follow-up are encouraging given the common negative attitudes toward dietary change in this population (13
). Previous studies have not assessed the impact of intervening to promote dietary change among Latinos with diabetes (5
). Our findings that self-monitoring twice per day or more was associated with improvements in glucose control is also relevant because the importance of blood glucose self-monitoring among patients with type 2 diabetes has been questioned (24
). Our emphasis on teaching participants to use glucose data to modify their diet intake or their activity may have contributed to our findings. The lack of an important intervention impact on physical activity may reflect the relatively weaker emphasis on exercise in the protocol and probably contributed to the nonsignificant intervention effect at 12 months. However, a previous study of Latinos with diabetes also failed to produce significant improvement in physical activity (6
Intervention attendance decreased during the follow-up phase of the intervention and correlated with the decreased impact of the intervention over time. While less than ideal, attendance rates reflect the reality of many health centers serving low-income populations (i.e., typically high cancellation and no-show rates). In contrast to efficacy studies, which recruit only highly motivated individuals (i.e., those able to demonstrate that they can adhere to study protocols before being considered for study enrollment), or clinical trials with advertisement-based recruitment methods (likely to recruit self-selected populations), we recruited from a general pool of patients with diabetes from health centers serving low-income communities, often regarded as “hard to reach.” A third factor contributing to the reduced change differences between intervention and control conditions was the slight improvement in HbA1c
observed in the control group. This finding is consistent with those of previous trials (25
), suggesting that participation in a trial per se, independent of any intervention, produces glucose control improvements. As in this study, such improvements are greater among individuals with higher baseline HbA1c
. With regression to the mean ruled out as a possible explanation for this phenomenon (3
), other mechanisms possibly accounting for HbA1c
improvements include contact and attention from research staff, information discussed during the screening, consenting and assessment sessions, and patient motivation. Laboratory results mailed to patients’ providers also could have influenced outcomes.
A limitation of this study was the self-reported nature of the behavioral data (diet and blood glucose self-monitoring). In addition, we were unable to objectively measure physician prescription patterns and patient medication adherence or estimate the mediating effect of medications on physiological outcomes. However, our measure of diabetes medications intensity showed no differences at baseline or over time between the intervention and the control groups. Another limitation was the lack of blood glucose variability for the usual-care group.
To our knowledge, this is the first large RCT to test a culturally tailored, literacy-sensitive diabetes self-management intervention for low-income Spanish-speaking Latinos of Caribbean origin. Unlike the two previous studies of diabetes interventions targeting Latinos (5
), this study recruited patients from real-world clinical settings; included comprehensive assessments of clinical, behavioral and theory-based constructs; and included assessment of factors mediating HbA1c
improvements. With currently climbing rates of obesity, the prevalence of diabetes and its associated complications will continue to increase among Latinos. Future studies will need to examine innovative ways to enhance diabetes self-management, especially long-term glycemic control, and the cost-effectiveness of these interventions.