Background
Major depression (MD) and alcohol use disorders (AUD) are both widely recognized as chronic conditions: people with these health conditions suffer from frequent relapses [
1],[
2], and approximately 10-30% of people with these disorders experience a long-lasting course, of more than 24 months [
2]-[
5].
Depressive disorders and AUD are also the most important contributors to the burden of mental disorders, as measured in disability-adjusted life years (DALYs), in the United States and Europe [
6],[
7]. The study of the clinical course for these health conditions should also include functioning measures, since people generally consider improved day-to-day functioning as a relevant part of their recovery process [
8]. Moreover, problems in functioning are strong predictors for subsequent relapses in these health conditions [
9],[
10].
The literature generally agrees that these health conditions are associated with incidence of disability [
11]-[
13]. Remission from symptoms is associated with functional improvements [
14]. Increasing evidence has been also reported regarding functional improvements as a result of different treatments [
15]-[
18]. However, few studies have analyzed disability trajectories during the chronic course of MD and AUD. In the case of chronic depression, some studies have found that longer duration is associated with higher disability [
19],[
20]. Other studies have suggested that higher disability is a function of greater severity of symptoms and comorbidity, rather than longer duration [
21]. However, none of these studies have jointly examined whether chronic MD is a risk factor for both incidence of disability and persistence of disability in the general population.
Regarding chronic AUD, one study has analyzed prospectively the incidence of disability in different chronic groups of AUD [
11]. Incidence of disability was found to be higher in people who moved from alcohol abuse to alcohol dependence. No changes in disability were associated with persistent alcohol abuse and persistent alcohol dependence. However, this study did not analyze whether the level of disability experienced by persistent alcohol dependence and persistent alcohol abuse groups was different to the disability experienced by the general population. This study did not analyze either other variables associated with changes in disability scores for the different groups of AUD.
Furthermore, the role of help-seeking behavior in the course of disability has rarely been studied. Generally, help-seeking behavior has been selected as a study outcome. For instance, one study reported that higher disability was an associated factor for help-seeking [
22]. Similarly, help-seeking behavior has been associated with better clinical outcomes [
23]. Only a single study, to our knowledge, has analyzed the role of use of health services in disability [
24]; however, it included both chronic and non-chronic MD patients.
Therefore, the present study aimed to 1) verify whether chronic AUD and chronic MD are risk factors for incidence and persistence of disability in the general population; and 2) specify whether, after controlling for some confounders, help-seeking behavior hinders from incidence of disability in chronic MD and chronic AUD.
Results
Prevalence estimates of disability
Prevalence estimates for persistence and incidence of disability are shown in Table
1. Persistence rates were generally higher than incidence rates for the general population and for the chronic MD and AUD groups. People with chronic MD experienced higher persistence of disability than the general population for all the SF-12 domains. However, only estimates of persistent problems in mental health-related domains were significantly higher in the chronic AUD group than in the general population.
Table 1
Prevalence estimates (95% CI) of persistence of disability and incidence of disability in the general population, population with chronic major depression, and population with chronic alcohol use disorders
Persistence of disability
| | | |
Physical functioning | 16.69% (16.22 to 17.16) |
28.33% (21.67 to 34.99)
|
10.15% (7.88 to 12.43)
|
Physical role | 14.80% (14.35 to 15.24) |
30.70% (23.96 to 37.44)
|
10.39% (8.09 to 12.69)
|
Bodily pain | 20.86% (20.34 to 21.38) |
43.42% (36.13 to 50.70)
| 21.07% (18.05 to 24.09) |
General health | 27.19% (26.62 to 27.76) |
45.91% (38.65 to 53.17)
| 27.27% (24.03 to 30.52) |
Vitality | 24.96% (24.40 to 25.52) |
63.82% (56.96 to 70.68)
| 26.16% (23.01 to 29.32) |
Social functioning | 11.71% (11.31 to 12.12) |
47.92% (40.69 to 55.16)
|
17.33% (14.51 to 20.14)
|
Emotional role | 14.06% (13.62 to 14.50) |
49.24% (41.97 to 56.50)
|
19.30% (16.37 to 22.24)
|
Mental health | 16.27% (15.80 to 16.74) |
56.58% (49.36 to 63.80)
|
22.92% (19.88 to 25.96)
|
Incidence of disability
| | | |
Physical functioning | 11.80% (11.39 to 12.21) |
18.97% (13.16 to 24.77)
| 10.99% (8.64 to 13.34) |
Physical role | 10.53% (10.13 to 10.93) | 9.76% (6.03 to 13.50) | 11.11% (8.98 to 13.25) |
Bodily pain | 15.81% (15.33 to 16.29) | 18.63% (12.87 to 24.38) | 15.54% (12.99 to 18.10) |
General health | 13.99% (13.54 to 14.44) | 11.99% (7.23 to 16.76) | 13.61% (11.15 to 16.07) |
Vitality | 19.03% (18.52 to 19.53) | 16.46% (11.40 to 21.53) | 19.78% (16.88 to 22.67) |
Social functioning | 14.15% (13.71 to 14.60) | 19.56% (13.48 to 25.63) | 16.79% (14.12 to 19.46) |
Emotional role | 16.08% (15.60 to 16.55) | 16.32% (10.58 to 22.05) | 19.18% (16.32 to 22.04) |
Mental health | 15.91% (15.43 to 16.38) | 18.73% (12.80 to 24.66) | 16.96% (14.25 to 19.66) |
In the general population and in the chronic AUD group, the highest prevalence of persistent disability was found for the general health domain (27.19%, 95% CI = 26.62 to 27.76, in the general population; 27.27%, 95% CI = 24.03 to 30.52 in the chronic AUD group). In contrast, persistent disability was highly prevalent for the vitality domain in the group of chronic MD (63.82%, 95% CI = 56.96 to 70.68). Regarding the incidence of disability, the prevalence estimates ranged from 10.53% (physical role) to 19.03% (vitality) in the general population. The highest incidence rates were found for social functioning (19.56%, 95% CI = 13.48 to 25.63) and vitality (19.78%, 95% CI = 16.88 to 22.67) in the chronic MD and chronic AUD groups, respectively.
Risk Factors for Disability in the General Population
Risk factors for disability in the general population are shown in Table
2. After controlling for socio-demographics and other health conditions, chronic MD was the strongest risk factor for persistence of disability in the emotional role, social functioning and mental health domains in the general population. The presence of physical health conditions was the main predictor of persistent disability in the physical functioning, physical role, bodily pain, general health, and vitality domains. Chronic AUD also had an impact on persistence of disability, except for in the physical-health related domains. Similar results were found in the analyses to determine risk factors for incidence of disability in the general population (Table
2). Chronic MD and the presence of physical health problems were the strongest risk factors for incidence of disability in physical functioning and bodily pain, while the presence of physical health problems was the strongest risk factor for incidence of disability in the remaining physical-health related domains. Moreover, chronic MD was the strongest risk factor for incidence of disability in the social functioning, vitality, emotional role and mental health domains. Chronic AUD was a risk factor for incidence of disability in the vitality, social functioning and emotional role domains. Lower family income, lower educational attainment and unemployment were related to persistence and incidence of disability in the general population.
Table 2
Odds ratio (95% CI) associated with predictors for persistence of disability and incidence of disability in the general population
Persistence of disability
| | | | | | | | |
Educational attainment | 0.92***(0.91 to 0.93) | 0.93***(0.92 to 0.94) | 0.95***(0.94 to 0.96) | 0.85***(0.84 to 0.86) | 0.97***(0.96 to 0.98) | 0.98***(0.97 to 0.99) | 0.97***(0.96 to 0.98) | 0.97***(0.96 to 0.98) |
Family income | 0.93***(0.92 to 0.94) | 0.93***(0.92 to 0.94) | 0.96***(0.95 to 0.97) | 0.94***(0.93 to 0.95) | 0.96***(0.95 to 0.97) | 0.94***(0.93 to 0.95) | 0.94***(0.93 to 0.95) | 0.96***(0.95 to 0.97) |
Unemployment | 1.38***(1.24 to 1.54) | 1.43***(1.28 to 1.58) | 1.13*(1.02 to 1.25) | 1.43***(1.30 to 1.57) | 1.06(0.97 to 1.17) | 1.50***(1.36 to 1.66) | 1.54***(1.39 to 1.70) | 1.48***(1.34 to 1.63) |
Physical health conditions | 3.25***(3.08 to 3.43) | 2.99***(2.83 to 3.15) | 3.40***(3.23 to 3.58) | 2.47 ***(2.35 to 2.60) | 2.19***(2.08 to 2.30) | 2.30***(2.18 to 2.43) | 1.95***(1.86 to 2.05) | 1.73***(1.64 to 1.82) |
Mental health conditions | 1.77***(1.67 to 1.88) | 1.64***(1.55 to 1.74) | 1.78***(1.68 to 1.88) | 1.55***(1.47 to 1.63) | 1.87***(1.78 to 1.97) | 2.45***(2.31 to 2.59) | 2.40***(2.27 to 2.54) | 2.26***(2.14 to 2.38) |
Major depression | 1.49***(1.34 to 1.65) | 1.50***(1.35 to 1.67) | 1.58***(1.43 to 1.74) | 1.50***(1.36 to 1.64) | 2.13***(1.93 to 2.35) | 2.74***(2.48 to 3.02) | 2.99***(2.71 to 3.30) | 3.30***(2.99 to 3.63) |
Alcohol use disorders | 0.96(0.86 to 1.06) | 0.99(0.90 to 1.09) | 1.16***(1.07 to 1.26) | 1.07(0.98 to 1.16) | 1.09*(1.01 to 1.18) | 1.35***(1.23 to 1.47) | 1.31***(1.21 to 1.43) | 1.17***(1.08 to 1.26) |
Incidence of disability
| | | | | | | | |
Educational attainment | 0.94***(0.92 to 0.96) | 0.94***(0.92 to 0.96) | 0.94***(0.93 to 0.96) | 0.87***(0.85 to 0.88) | 0.97***(0.95 to 0.98) | 0.96***(0.95 to 0.98) | 0.95***(0.93 to 0.97) | 0.95***(0.93 to 0.96) |
Family income | 0.96***(0.95 to 0.97) | 0.96***(0.95 to 0.97) | 0.99(0.98 to 1.01) | 0.96***(0.95 to 0.97) | 0.98***(0.97 to 0.99) | 0.96***(0.95 to 0.97) | 0.96***(0.95 to 0.97) | 0.98***(0.97 to 0.99) |
Unemployment | 1.71***(1.39 to 2.10) | 1.50***(1.22 to 1.85) | 1.47***(1.23 to 1.76) | 1.31**(1.07 to 1.61) | 1.18(0.98 to 1.43) | 1.60***(1.33 to 1.93) | 1.21(0.99 to 1.48) | 1.41***(1.17 to 1.71) |
Physical health conditions | 1.96***(1.76 to 2.18) | 1.67***(1.49 to 1.88) | 1.89***(1.70 to 2.11) | 1.58***(1.41 to 1.78) | 1.48***(1.34 to 1.64) | 1.54***(1.39 to 1.70) | 1.52***(1.38 to 1.67) | 1.25***(1.13 to 1.38) |
Mental health conditions | 1.33***(1.18 to 1.51) | 1.37***(1.21 to 1.56) | 1.37***(1.22 to 1.54) | 1.04(0.91 to 1.17) | 1.27***(1.14 to 1.43) | 1.47***(1.31 to 1.64) | 1.46***(1.30 to 1.64) | 1.30***(1.15 to 1.46) |
Major depression | 2.06***(1.49 to 2.84) | 1.29(0.90 to 1.86) | 2.02***(1.41 to 2.88) | 1.44*(1.01 to 2.10) | 3.05***(2.00 to 4.67) | 4.44***(3.02 to 6.52) | 3.66***(2.31 to 5.82) | 4.82***(3.03 to 7.68) |
Alcohol use disorders | 1.19(0.94 to 1.50) | 1.22(0.98 to 1.51) | 1.19(0.98 to 1.45) | 1.03(0.83 to 1.27) | 1.28*(1.05 to 1.54) | 1.46***(1.20 to 1.78) | 1.59**(1.31 to 1.92) | 1.19(0.97 to 1.46) |
Risk factors for disability in people with chronic MD
Table
3 shows the risk factors for persistence and incidence of disability in respondents with chronic MD. Physical comorbidity was the strongest risk factor for persistence of disability in the physical functioning, physical role, bodily pain, general health, and vitality domains for respondents with this health condition. MD was also associated with social functioning and emotional role. Help-seeking behavior was significantly associated with persistent problems in the physical functioning, physical role, general health and emotional role domains. Severity of depressive symptoms was a risk factor for persistence in the general health, social functioning, emotional role and mental health domains. Low family income was related with persistence of disability for all SF-12 domains except for bodily pain and physical role, while unemployment and low educational attainment were related with persistence of disability in some of the physical health-related domains.
Table 3
Odds ratio (95% CI) associated with predictors for persistence of disability and incidence of disability, in the population with chronic major depression
Persistence of disability
| | | | | | | | |
Educational attainment | 0.88*(0.77 to 0.98) | 0.96(0.85 to 1.08) | 0.89(0.79 to 1.01) | 0.82**(0.72 to 0.93) | 1.00(0.88 to 1.13) | 1.05(0.93 to 1.17) | 0.99(0.89 to 1.11) | 0.93(0.82 to 1.06) |
Family income | 0.92**(0.87 to 0.98) | 0.95(0.90 to 1.01) | 0.97(0.92 to 1.03) | 0.94*(0.89 to 0.99) | 0.92**(0.87 to 0.98) | 0.91**(0.86 to 0.96) | 0.92**(0.87 to 0.98) | 0.90**(0.84 to 0.95) |
Unemployment | 1.39(0.68 to 2.82) | 1.96*(1.04 to 3.68) | 1.42(0.66 to 3.05) | 1.33(0.79 to 2.23) | 2.57*(1.06 to 6.24) | 1.48(0.64 to 3.40) | 1.02(0.44 to 2.34) | 1.68(0.57 to 4.93) |
Physical health conditions | 4.00***(2.29 to 6.97) | 5.11***(2.96 to 8.80) | 4.87***(2.71 to 8.73) | 2.25**(1.35 to 3.75) | 3.34***(1.75 to 6.38) | 1.77*(1.06 to 2.98) | 2.29*(1.20 to 4.37) | 1.58(0.86 to 2.88) |
Mental health conditions | 1.10(0.69 to 1.75) | 0.84(0.53 to 1.33) | 1.12(0.74 to 1.69) | 1.20(0.84 to 1.72) | 0.63(0.36 to 1.08) | 1.19(0.75 to 1.87) | 1.17(0.73 to 1.88) | 1.04(0.62 to 1.75) |
Severity of depression | 1.03(0.86 to 1.23) | 1.09(0.93 to 1.27) | 1.11(0.93 to 1.32) | 1.32**(1.12 to 1.55) | 1.20(0.99 to 1.46) | 1.40***(1.18 to 1.66) | 1.28*(1.03 to 1.58) | 1.25*(1.03 to 1.52) |
Seeking help for major depression | 2.01**(1.19 to 3.38) | 1.73**(1.16 to 2.58) | 1.52(0.96 to 2.42) | 1.57*(1.05 to 2.36) | 1.71(0.96 to 3.03) | 1.43(0.88 to 2.32) | 1.80*(1.04 to 3.10) | 1.48(0.82 to 2.65) |
Incidence of disability
| | | | | | | | |
Educational attainment | 0.78*(0.64 to 0.96) | 0.92(0.73 to 1.17) | 0.91(0.73 to 1.14) | 0.70*(0.54 to 0.92) | 0.83(0.62 to 1.11) | 0.82(0.64 to 1.05) | 0.78(0.57 to 1.07) | 0.65*(0.45 to 0.95) |
Family income | 0.98(0.89 to 1.07) | 0.94(0.84 to 1.06) | 0.98(0.88 to 1.10) | 1.01(0.87 to 1.16) | 1.03(0.89 to 1.19) | 0.86*(0.74 to 0.98) | 1.08(0.92 to 1.25) | 1.03(0.87 to 1.21) |
Unemployment | 3.98*(1.05 to 15.07) | 1.24(0.25 to 6.26) | 0.95(0.14 to 6.26) | 1.55(0.17 to 14.17) | 12.87*(1.15 to 144.69) | 0.40(0.08 to 1.98) | 0.11(0.01 to 1.58) | 0.15(0.01 to 4.42) |
Physical health conditions | 3.13*(1.01 to 9.78) | 0.92(0.14 to 5.99) | 2.54(0.58 to 11.10) | 4.80*(1.30 to 17.71) | 14.66*(1.12 to 192.35) | 6.38*(1.42 to 28.67) | 4.19(0.68 to 25.93) | 1.19(0.26 to 5.50) |
Mental health conditions | 1.51(0.55 to 4.14) | 0.80(0.29 to 2.20) | 1.15(0.45 to 2.97) | 1.21(0.40 to 3.71) | 2.09(0.62 to 7.04) | 1.13(0.31 to 4.08) | 0.51(0.15 to 1.67) | 1.60(0.33 to 7.67) |
Severity of depression | 0.74(0.50 to 1.09) | 0.97(0.62 to 1.51) | 0.89(0.63 to 1.27) | 0.79(0.54 to 1.15) | 1.30(0.80 to 2.10) | 1.07(0.63 to 1.80) | 1.20(0.84 to 1.73) | 0.69(0.43 to 1.12) |
Seeking help for major depression | 0.60(0.20 to 1.75) | 0.73(0.21 to 2.50) | 1.54(0.51 to 4.69) | 0.98(0.26 to 3.71) | 0.58(0.11 to 3.05) | 1.73(0.49 to 6.07) | 4.85(0.70 to 33.60) | 6.81**(1.83 to 25.43) |
Regarding incidence of disability, unemployment was the strongest risk factor for the physical functioning (OR = 3.98; 95% CI = 1.05 to 15.07) and vitality (OR = 12.87; 95% CI = 1.15 to 144.69) domains. Comorbidity with physical health conditions was a risk factor for incident disability in physical functioning, general health, vitality and social functioning. Finally, help-seeking behavior was significantly related to incidence of disability in the mental health domain (OR = 6.81; 95% CI = 1.83 to 25.43).
Risk factors for disability in people with chronic AUD
Finally, the results for the chronic AUD group are shown in Table
4. Regarding persistence of disability, comorbid physical disorders had the highest impact on the physical functioning, physical role, bodily pain, social functioning, vitality and general health domains, while the comorbid mental disorders variable was the strongest risk factor for mental health-related domains. Severity of AUD was associated with persistent disability for all SF-12 domains. Unemployment was strongly related with persistent disability in mental health (OR = 2.10; 95% CI = 1.38 to 3.20). Help-seeking behavior was marginally related with persistence of disability in social functioning (OR = 1.55, 95% CI = 0.99 to 2.45;
p = 0.058).
Table 4
Odds ratio (95% CI) associated with predictors for persistence of disability and incidence of disability, in the population with chronic alcohol use disorders
Persistence of disability
| | | | | | | | |
Educational attainment | 0.94(0.86 to 1.03) | 0.92(0.85 to 1.01) | 0.93*(0.87 to 0.99) | 0.83***(0.77 to 0.90) | 1.04(0.97 to 1.11) | 1.05(0.99 to 1.12) | 1.05(0.98 to 1.12) | 1.02(0.96 to 1.09) |
Family income | 0.92**(0.90 to 0.95) | 0.95*(0.92 to 0.98) | 0.95***(0.92 to 0.97) | 0.96**(0.94 to 0.98) | 0.98(0.95 to 1.01) | 0.98(0.96 to 1.01) | 0.97**(0.94 to 0.99) | 0.99(0.96 to 1.01) |
Unemployment | 1.71**(1.10 to 2.67) | 2.05**(1.28 to 3.29) | 1.30(0.87 to 1.96) | 1.75*(1.14 to 2.69) | 1.01(0.68 to 1.49) | 1.53*(1.02 to 2.31) | 1.40(0.91 to 2.16) | 2.10**(1.38 to 3.20) |
Physical health conditions | 3.16***(2.27 to 4.41) | 2.91***(2.06 to 4.12) | 3.06***(2.22 to 4.21) | 3.11***(2.28 to 4.23) | 1.64**(1.20 to 2.25) | 2.05***(1.48 to 2.84) | 1.51**(1.08 to 2.10) | 1.40*(1.02 to 1.92) |
Mental health conditions | 1.49***(1.10 to 2.02) | 1.74**(1.29 to 2.36) | 1.47**(1.14 to 1.90) | 1.46**(1.15 to 1.85) | 1.59***(1.27 to 2.00) | 2.04***(1.57 to 2.66) | 2.24***(1.74 to 2.88) | 2.09***(1.64 to 2.66) |
Severity of alcohol use | 1.13**(1.05 to 1.22) | 1.13***(1.05 to 1.21) | 1.12***(1.06 to 1.18) | 1.11***(1.05 to 1.17) | 1.14***(1.07 to 1.20) | 1.23***(1.16 to 1.31) | 1.21***(1.14 to 1.28) | 1.17***(1.10 to 1.23) |
Seeking help for drinking problems | 1.17(0.71 to 1.94) | 1.02(0.60 to 1.74) | 0.95(0.63 to 1.43) | 0.88(0.57 to 1.34) | 1.11(0.73 to 1.68) | 1.55(0.99 to 2.45) | 1.06(0.70 to 1.59) | 1.28(0.84 to 1.97) |
Incidence of disability
| | | | | | | | |
Educational attainment | 0.93(0.81 to 1.06) | 0.92(0.81 to 1.03) | 0.91(0.82 to 1.02) | 0.86*(0.76 to 0.98) | 0.98(0.88 to 1.09) | 1.02(0.91 to 1.14) | 1.01(0.91 to 1.12) | 0.98(0.87 to 1.09) |
Family income | 0.94(0.87 to 1.01) | 1.03(0.97 to 1.08) | 0.96(0.91 to 1.01) | 0.98(0.93 to 1.03) | 1.00(0.96 to 1.05) | 1.00(0.95 to 1.04) | 1.02(0.97 to 1.07) | 1.00(0.95 to 1.05) |
Unemployment | 1.95(0.80 to 4.75) | 1.91(0.83 to 4.38) | 1.46(0.66 to 3.20) | 2.48*(1.03 to 5.94) | 1.65(0.70 to 3.87) | 3.11**(1.47 to 6.58) | 1.46(0.67 to 3.19) | 1.54(0.65 to 3.67) |
Physical health conditions | 1.84(0.95 to 3.56) | 3.16***(1.71 to 5.86) | 1.74(0.93 to 3.27) | 1.30(0.60 to 2.83) | 1.39(0.77 to 2.51) | 1.48(0.83 to 2.64) | 1.72(0.94 to 3.12) | 0.94(0.51 to 1.72) |
Mental health conditions | 1.35(0.69 to 2.62) | 1.33(0.73 to 2.42) | 1.19(0.71 to 1.98) | 1.83*(1.04 to 3.19) | 1.41(0.84 to 2.37) | 1.62(0.99 to 2.64) | 1.42(0.82 to 2.46) | 1.21(0.68 to 2.15) |
Severity of alcohol use | 1.13(0.99 to 1.27) | 1.07(0.94 to 1.21) | 1.01(0.90 to 1.13) | 1.02(0.91 to 1.14) | 1.01(0.91 to 1.12) | 1.05(0.93 to 1.18) | 1.24***(1.11 to 1.38) | 1.05(0.95 to 1.17) |
Seeking help for drinking problems | 1.94(0.80 to 4.72) | 1.62(0.74 to 3.57) | 2.13(0.99 to 4.55) | 1.46(0.59 to 3.61) | 1.36(0.60 to 3.09) | 1.71(0.80 to 3.65) | 1.52(0.68 to 3.38) | 1.30(0.57 to 2.94) |
Regarding incidence of disability, comorbidity with mental disorders was a predictor for developing disability in general health (OR = 1.83; 1.04 to 3.19). Comorbidity with physical disorders was the strongest risk factor for worsening in the physical role domain (OR = 3.16; 95% CI = 1.71 to 5.86). Additionally, severity of AUD was a relevant risk factor for incident disability in emotional role, and was marginally associated with the incidence of disability in physical functioning (OR = 1.13, 95% CI = 0.99 to 1.27; p = 0.052). Help-seeking behavior was not significantly associated with incident disability, but some marginally significant trend of relationship could be observed; for example, in bodily pain (OR = 2.13, 95% CI = 0.99 to 4.55; p = 0.052). Lower family income was also marginally related with incidence of disability in physical functioning and bodily pain.
Discussion
The present study is the first to prospectively examine whether chronic course of MD and chronic AUD are risk factors for incidence and persistence of disability in the general population as well as to report specific risk factors for incidence and persistence of disability in these health conditions.
We found that, by and large, prevalence estimates for persistence of disability were higher than for incidence in the general population, as well as among respondents with chronic MD or chronic AUD. This is an expected result, if we consider that NESARC included on average three years between time assessments, and this period may not be a long enough interval to study incidence of disability in a relatively younger community-dwelling population.
Our findings clearly indicate that chronic MD is a risk factor for persistent disability in the general population. This is congruent with previous studies reporting that a long-lasting course of MD is associated with persistent disability [
41],[
42]. People at higher risk of chronic depression may require longer treatments to avoid a persistent course of disability. According to relevant experts [
43], key components of these treatments may be longer treatment periods and careful adherence monitoring.
Another important finding of the present study is that even after controlling for other potential confounders, chronic MD was associated with incidence of disability in a variety of domains. This finding is in the line with a previous longitudinal study [
19]. However, other studies have reported that recurrence and longer duration of depression were not risk factors for higher disability in MD [
21],[
24],[
44]. Several methodological differences might explain these differences. Firstly, chronicity was not measured prospectively in these previous studies. Secondly, recurrence and persistence were analyzed separately. In addition, disability scores were compared to patients with non-chronic depression and not to the general population, as done here. All these differences hinder study comparisons. Nevertheless, future longitudinal studies should compare whether individuals with chronic and non-chronic depression present similar risk for persistence and incidence of disability.
Our results also indicate that the presence of chronic AUD is a risk factor for persistence of disability in a wide range of functional areas, except for physical health-related domains. Some studies have previously reported that AUD are associated with mental health-related problems rather than physical ones [
45],[
46]. These results could be explained by the fact that physical problems might be associated with comorbidity and social exclusion factors, particularly frequent in people with AUD [
47]. Nevertheless, our findings suggest that chronic AUD might be considered an important risk factor for chronic disability in the general population. Treatments in AUD should be aimed at improving all those functional areas suffering long-lasting impairment, not only focusing on achieving complete long-term abstinence.
On the other hand, chronic AUD were risk factors for incidence of disability in the domains of vitality, social functioning and emotional role. This finding may suggest that disability in chronic AUD could be mostly persistent, and that only specific areas might be at higher risk of worsening over time. However, further studies should verify whether chronic AUD are risk factors for both incidence and persistence of disability over the longer term.
In addition, the present study is the first to analyze a wide range of risk factors for both persistence and incidence of disability in people with chronic MD and AUD. Comorbid physical disorders were strong risk factors for persistence of disability for most of the domains in both MD and AUD. This finding is congruent with the idea that physical comorbidity among mental disorders is highly disabling [
33]. Further research is necessary to test tailored mental health interventions for people with comorbid physical disorders [
48], since people with physical diseases (particularly some cardiovascular and liver diseases) have been frequently excluded from psychopharmacological trials.
Another important finding was that help-seeking behavior for mood problems was related to persistent disability in chronic MD. This outcome might be explained by the fact that people with MD seek help when they are suffering from more severe disability [
49],[
50]. In contrast, health care -seeking behavior for drinking problems was not significantly related to persistence of disability in people with chronic AUD. This finding might suggest that people with chronic AUD did not seek help in spite of suffering from persistent problems of functioning. More comprehensive treatment approaches, rather than emphasizing immediate abstinence, might be necessary to motivate treatment entry in persons with AUD [
51]. As opposed to our hypothesis, help-seeking behavior at Wave 1 did not protect from incidence of disability at Wave 2 in the either group, whether chronic MD or AUD. In addition, help-seeking behavior was identified as a risk factor for incidence of disability at Wave 2, specifically for mental health in the MD group, and marginally for bodily pain in AUD. There may be different reasons that explain why help-seeking behavior did not provide protection from incidence of disability. One is that people with chronic AUD and MD who were seeking help at baseline scored significantly lower in self-perception of health (results available at authors’ request). It has been previously reported in the literature that self-perception of health is longitudinally related to level of functioning [
52]; consequently, respondents who had already sought help at baseline could suffer from sub-threshold severe problems, and easily developed incidence of severe disability more often. Another possible explanation could be that help-seeking behavior has nothing to do with receiving high-quality treatment or with treatment compliance, which could be the factors directly related to better functional outcomes [
53]. Further studies should confirm how help-seeking behavior is related to subsequent disability.
As expected, higher severity of symptoms was also related to persistence of disability in all of the SF-12 domains in AUD, and for mental-health related domains in the MD group. However, severity was not as strong a risk factor for disability as has been reported in previous studies [
44]. In addition, a higher number of symptoms was not a relevant factor for developing new disability for either the AUD or MD groups. This finding could be due to people with comorbid health conditions also experiencing higher severity of symptoms.
Regarding socio-demographic variables, unemployment was a risk factor for persistence and incidence of disability in the general population. Consequently, societies with high rates of unemployment are at higher risk for developing severe and chronic disability. More effective policies should be applied to face the rates of unemployment that the US and some European countries are still suffering, particularly among the younger and less educated populations [
54]. Unemployment was also related to persistent disability for a variety of disability domains in both chronic MD and AUD, and with incidence of disability in chronic MD. Previous studies have already shown that people with mental disorders are vulnerable to being unemployed and to losing their jobs [
55]. More efforts should be made to ensure employment equity for people with mental problems.
Analyzing other demographic risk factors in the groups of specific health conditions, the current findings also confirm that the burden of chronic MD may be particularly dramatic for people with less resources, since lower family income and a lower education level were also risk factors for persistent disability in chronic MD. Lower income was also marginally related with incidence of disability in some physical health-related domains in chronic AUD. Mental health policymakers should focus their efforts on people with less resources in order to address the inequalities that mental disorders cause. The literature has suggested some actions that can promote mental health, maintaining good health care services and not compromising the care of citizens in times of economic recession [
56].
The present study should be also interpreted with the following limitations in mind. Our report has defined incidence of disability by the significant switch from a “normal” level of functioning to an “impaired” level of functioning. Persistence of disability was defined by the maintenance of the same impaired level of functioning. Although our definition of disability based on 25th percentile has been previously used for describing disability in the normal US population [
31] and to report incidence of disability [
57], we acknowledge that disability is well-established as a continuum [
58]. Particularly, our definition of incidence of disability neither provides information on the importance of the observed change nor considers relevant disability changes along all the possible SF-12 scores. One possible measure that might have been used is the decrease by more than one Standard Deviation (SD) of SF-12v2 scores from Wave 1 to Wave 2. However, the 25th percentile-based definition has been driven by the following reasons: firstly, to define persistence and incidence of disability likewise throughout the whole study; secondly, some SF-12v2 norm-based scores displayed only five possible values in our sample. Consequently, the use of a SD changes-based measure was not suitable for variables including limited number of values; thirdly, distribution change-based criteria are linked to the assumption that measurement error is constant across the range of possible scores. However, one study has reported that smaller SD are usually given at both scoring extremes [
59]. Finally, whereas one amount of SD change may be perceived as highly important for some functioning domains along the disability continuum, the same amount can be perceived as less relevant in others. Nevertheless, to verify whether the use of this cut off-point (25th percentile) might have altered our results, two sensitivity analyses were conducted considering the 20th percentile and the 30th percentile in the SF-12 domains as other possible cut-off points for disability. The results obtained using these cut-off points were similar to those reported in the present paper (these data are available upon request). Another important limitation was that prevalence of incidence of disability was generally low. These small sample sizes had an impact on the statistical power of our analyses, specifically in the group of chronic MD (less than 100 observations). Hence, the lack of significant findings in the analyses of incidence should be interpreted with caution. Finally, although the measures of severity of symptoms for AUD and MD have been used previously, counting the number of symptoms is an indirect approach to assess severity, and it might have nothing to do with the clinical severity of symptoms [
60].
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Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
All listed authors participated meaningfully in the study and they have seen and approved the final manuscript. Authors’ contributions were: MC conceptualized and oversaw analyses, and wrote the article. FFC carried out the statistical analyses, and contributed to the writing of the article. SC revised the statistical analysis and contributed to the interpretation of data. SC, AC, JLAM, reviewed the first draft of the manuscript. MC, SC, AC, JLAM, designed the study, oversaw all aspects of the study implementation, and contributed to the writing of the article. All authors made critical revision of the manuscript for important intellectual content. All authors read and approved the final manuscript.