In this study, we assessed HRQoL and depression to evaluate the overall burden of T2D and associated risk factors on general health status (SF-12) and more specifically on mental health (PHQ-9). The SHIELD data demonstrate that respondents with T2D and those with a high number of risk factors (3
) have a self-reported lower HRQoL, compared with those having a lower number of risk factors (0–2), as well as the general population. Respondents with T2D and those with high risk reported significant decrements in physical health HRQoL compared with those with low risk, even after adjusting for modifiable and non-modifiable characteristics. Nearly 50% of those with T2D and those with high risk reported some limitation in the physical component, including work or moderate activities. This study also provided new evidence of decreased HRQoL and increased depressive symptoms among individuals at high risk for T2D but who were not currently diagnosed or treated as well as among those with diagnosed T2D. Ratings of HRQoL and depression in respondents with T2D and those at high risk of T2D were remarkably similar but significantly different from low-risk respondents. This observation may indicate that the accumulation of risk factors for T2D is altering HRQoL before a diagnosis is made.
Additionally, these results showed that health and disease status affected the emotional health of those with T2D and those with high risk in greater proportion than reported by the lower-risk group. In general, HRQoL decrements were greater for physical domains than for emotional or mental domains, but depression as measured by the PHQ-9 was significantly greater in the T2D and high-risk groups. A greater percentage of respondents with T2D and with high risk reported being moderately to severely depressed compared with the low-risk group.
Also evident in this study was the impact that demographic factors, such as age and income, have on individuals’ HRQoL. Those respondents with lower incomes, increased age, and who were obese, at high risk or with a T2D diagnosis reported lower HRQoL scores, after adjusting for non-modifiable risk factors (gender, race, geographic region and household size). These findings confirmed those in the Canadian National Population Survey, (18
) where T2D had a greater impact on HRQoL for older ages and low socio-economic status.
The present study confirms the lower HRQoL among T2D respondents that has been observed in other investigations (4
). Impaired physical and social functioning but not mental functioning among diabetes mellitus patients was observed in the present study as well as prior studies that utilised the SF-36 general measure (19
). Moreover, the present study observed the impact of T2D on HRQoL in a significantly larger population-based sample (n
= 3530 T2D) than previous investigations (n
= 221–254) (19
). However, these prior investigations typically compared T2D patients with the general population (18
), whereas this study demonstrated lower HRQoL among T2D and high-risk respondents when compared with low-risk respondents. The greater number of risk factors for T2D significantly impacted HRQoL in our study sample, similar to analyses of the Medical Expenditure Panel Survey, which showed that individuals with a cluster of similar cardiometabolic risk factors had a significant decrease in physical functioning (PCS-12) but not mental functioning (22
The MCS of the SF-12 did not differentiate risk groups as well as the PCS. The MCS scores were significantly higher for the low-risk than the high-risk or T2D groups, only after adjusting for other covariates such as age, race and gender. Further, the mental health component of the SF-12 did not differentiate risk groups as well as the PHQ-9 depression questionnaire. The PHQ-9 scores demonstrated that the low-risk group had significantly lower scores and smaller per cent of respondents with moderate-to-severe depression compared with the high-risk and T2D groups. Significant differences were observed among the low-risk as compared with the high-risk and T2D respondents for each of the nine items in the PHQ-9. These findings may indicate that the mental health component of the SF-12 may not be sufficiently sensitive to differentiate the groups on the impact of risk status on depression, whereas the PHQ-9 was especially as the MCS is a more general assessment of emotional problems and their impact on work, daily activities and social activities rather than depressive symptoms. The PHQ-9 not only has nine focused questions on depressive symptoms but also is more specific than the MCS for frequency of symptoms (not at all, several days, more than half the days and nearly every day).
This study provides evidence of the impact on HRQoL and depression in a large sample of T2D, high-risk and low-risk groups with a high survey response rate who are representative of the US population. Additionally, the evaluation of HRQoL and depression was carried out using standardised, validated measures so that normative-based results are provided. However, there are limitations to the study that should be considered. Only a small percentage (5–8%) of consumers invited to participate in the TNS panel elect to do so and those who participate are accustomed to completing surveys, leading to the possibility of selection bias. Household panels tend to under-represent the very wealthy and very poor segments of the population, and do not include military or institutionalised individuals. However, these limitations are true for most random sampling and clinically based methodologies. Additionally, the determination of T2D, high-risk and low-risk status was made based upon self-report rather than clinical or laboratory measures for blood glucose, hypertension, cholesterol, height and weight. It should also be noted that other comorbidities in the high-risk respondents, as well as those diagnosed with T2D, may contribute to their overall health burden and HRQoL. However, it is difficult to disentangle the HRQoL effects of such comorbidities from those of the risk factors or T2D, as many of these conditions are related to or a result of having the risk factors or T2D.