In this randomized controlled trial in patients with type 2 diabetes, we found an improvement in some aspects of both physical and emotional HRQoL in the group that was randomized to 3 months with the step promoting smartphone app DiaCert, compared to the control group receiving routine care. No long-term effects were seen after 6 months of follow-up, i.e., 3 months after the intervention had ended. Furthermore, being randomized to use the DiaCert-app did not have a statistically significant effect on the primary outcome (moderate to vigorous physical activity) or secondary outcomes of HbA1c, BMI, waist circumference, serum lipids or blood pressure (unpublished data).
The presence of diabetes per se is a known risk factor for impaired HRQoL, but several studies also show that HRQoL is even lower if diabetes complications are present [7, 30]. In a review on HRQoL among patients with diabetes in the Nordic countries , the presence of diabetes complications had the greatest impact on HRQoL. Two of the included studies, that comprised both patients with type 1 and type 2 diabetes, found a greater difference in HRQoL between patients with type 2 diabetes and the general population, than of type 1 diabetes and the general population [31, 32]. In another study by Wändell et al. , patients with both type 2 diabetes and angina pectoris showed lower HRQoL than those with only angina pectoris. Similarly, HRQoL was found to be lower in patients with diabetes or hypertension, compared to healthy individuals .
However, in a meta-analysis by Jing et al. physically active persons with type 2 diabetes had a better HRQoL in five of the included health concepts when measured using the SF-36 questionnaire, compared to less physically active persons. Comparable to our study, the health concept scores role limitations due to physical health problems and emotional well-being were two of the health concepts that showed an effect in the study . This might imply that the physical activity aspect of using the app DiaCert affects these health concepts in a positive way. However, better HRQoL in patients with type 2 diabetes has been shown to be associated with regular care, continuity of care, education by a diabetes nurse, and satisfaction with diabetes education . The daily support from an app might also affect the HRQoL. With a growing diabetes population, strategies to support patients to improve HRQoL are needed.
Several studies have evaluated the effect of apps on health outcomes among patients with diabetes. However, few have studied the effect on HRQoL in patients with type 2 diabetes, and, to the best of our knowledge, even fewer apps have focused on physical activity alone. The majority of apps previously studied are heterogeneous in the functions they provide [18, 19]. In a review by Veazie et al. , studies evaluating five commercially available apps for self-management of type 2 diabetes were included, but none of them targeted physical activity. Further, only one of the included studies evaluated the effect on HRQoL, and no difference in change in HRQoL was presented between the intervention and control group . This is in line with another review and meta-analysis by Bonoto et al. . They included six studies on efficacy of apps for patients with type 2 diabetes, where only one study by Holmen et al.  measured HRQoL. The patient group in the study by Holmen et al. was similar to ours, consisting of 59%, men with a mean age of 57 years, and a mean BMI of 31.7 kg/m2. However, their app did not focus on physical activity alone, but also targeted other aspects of self-management, e.g., diet. They conducted a 3-arm randomized controlled trial (RCT) with two intervention groups, both using the app, while one also received telephone counseling with a diabetes nurse. The control group received routine care. No improvement in HRQoL was seen in any of the three groups after 4 months and 1 year of intervention, respectively [37, 38]. This is in contrast to our study, as we found an effect on some aspect of HRQoL, immediately after 3 months of usage of the app.
Nevertheless, in a recent two group RCT by Coombes et al. , 30 participants with type 2 diabetes were randomized to either a 3 month long physical activity intervention, or to a control group receiving usual care. The intervention consisted of weekly exercise sessions and a wrist-worn heart rate monitor connected to a smartphone app, which informed the user if they performed enough physical activity. The sample size in the study by Combes et al. was smaller than ours, but the patient group was similar to ours, consisting of 67% men, with a mean age of 61 years, and a mean BMI of 30.8 kg/m2. Comparable to our study, the intervention group had a significant improvement in the health concept score role limitations due to emotional problems, compared to the control group. Long-term effects were however not studied.
The improvements seen in HRQoL at the 3 month follow-up in our study were not maintained after 6 months of follow-up, i.e., 3 months later, when participants had not had access to the app for 3 months. This may suggest that active support from the app is necessary for sustained change. Our results are comparable to the results of a study by van der Weegen et al. . In their 3-armed RCT, patients with chronic obstructive pulmonary disease or type 2 diabetes were randomized to one of three groups. One of the interventions consisted of the use of an accelerometer linked to a smartphone and Web app, combined with physical activity counseling with a nurse, while the other intervention group only received the physical activity counseling. The third group received routine care only. At the end of the intervention, participants receiving the interventions had improved in mental health aspects of HRQoL compared to participants in the group that received routine care only. However, this was not maintained at an additional follow-up 3 months later . Different to our study, the population studied  did not only comprise patients with type 2 diabetes, and the use of the app by itself was not studied. Nevertheless, reviews on mHealth interventions in patients with diabetes that have studied the long-term intervention effects have suggested a trend of decreasing intervention effect over time, which is in line with both our results and the results by Weegen et al. [40,41,42].
A strength of our study is the comparatively large sample size. With 166 participants included in our analyses, our analytical sample is larger or comparable with other studies that have evaluated the effect of apps on HRQoL among patients with type 2 diabetes [36, 37, 39, 40]. Further, participants were recruited from five primary care centers and one specialized medical center located in different areas with diverse populations and levels of socioeconomic status. Our study included a larger number of men compared to women, which reflects the higher prevalence of diabetes type 2 among men, compared to women in Sweden [43,44,45]. The ratio of men and women, the age of the participants, as well as the recruitment from several primary care centers show external validity, i.e., the generalizability of the study results to the general type 2 diabetes population external to the study population. Moreover, the RAND-36 has previously been used by patients with type 2 diabetes [8, 25,26,27], and the Swedish version of the RAND-36 has been found to be valid, reliable, responsive, and sensitive [46, 47].
Another strength of our study is the follow up at 6 months, i.e., 3 months after the intervention ended. It is conceivable that 3 months is too short a time for and intervention like this and that daily self-measurement and continuous support using behavioral change techniques is needed to keep the initial improvement in HRQoL over time. However, it should be noted that adherence to the use of the app is unknown, which is a limitation of the study. Furthermore, 22% of the RAND-36 data is missing at follow-up. This is comparable with the follow-up in the study by Holmen et al. where 21% of self-reported data, including HRQoL, was missing . Moreover, in the study by Wayne et al. 35% of the trial completers had missing HRQoL data at the 6 months follow up .
Limitations of our study include that the participants were non-blinded to their group allocation. Although the participants in the control group were not aware of what was included in the app during the intervention period, some controls could have found other ways to improve their physical activity, and thereby also affect their HRQoL. Potentially, since participants knew they would receive access to the app at the 6 months follow up, the risk of e.g., using a commercially available app promoting physical activity was reduced.
With a mean age of 60 years, the participants were younger than the general patient with type 2 diabetes in Sweden, with a mean age of 68 years [44, 45]. This may be due to the inclusion criteria of having a smartphone. However, 9 of 10 Swedes use a smartphone regularly . With a growing diabetes population and more people using smartphones, support from an app could be used as a strategy to improve short term HRQoL. However, apps developed for patients should undergo rigorous scientific evaluation.