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The incidence risk of type 2 diabetes mellitus in female nurses: a nationwide matched cohort study

  • Hsiu-Ling Huang1, 2,
  • Cheng-Chin Pan3,
  • Shun-Mu Wang1,
  • Pei-Tseng Kung4,
  • Wen-Yu Chou5 and
  • Wen-Chen Tsai5Email author
BMC Public HealthBMC series – open, inclusive and trusted201616:443

https://doi.org/10.1186/s12889-016-3113-y

Received: 17 December 2015

Accepted: 12 May 2016

Published: 26 May 2016

Abstract

Background

Diabetes is one of the most common chronic illnesses worldwide. This study was to assess whether the incidence risk of type 2 diabetes mellitus between female nurses and female non-nurses.

Methods

Study data were obtained from the Longitudinal Health Insurance Research Database, and nurses were sampled from the Registry for medical personnel. Nurses and non-nurses with similar traits and health conditions were selected via 1:1 propensity score matching. A total of 111,670 subjects were selected (55,835 nurses and 55,835 non-nurses). Stages of diabetes development were monitored until December 31, 2009. The Cox proportional hazards model was used to discuss risks and influencing factors related to diabetes. Poisson distribution methods were used to examine the incidence rate of diabetes per 1,000 person-years.

Results

The propensity matching results show that on average, female nurses who were diagnosed with diabetes were younger compared with the non-nurses (46.98 ± 10.80 vs. 48.31 ± 10.43, p <0.05). However, the results of the Cox proportional hazards model show that the nurses showed a lower risk of developing diabetes compared with the non-nurses (Adj. HR = 0.84, 95 % CI: 0.79–0.90). Factors influencing diabetes development risks among the nurses include advanced age and high Charlson Comorbidity Index levels.

Conclusion

The low degree of diabetes development among the nurses may be attributable to the fact that nurses possess substantial knowledge on health care and on healthy behaviors. The results of this study can be used as a reference to assess occupational risks facing nursing staff, to prevent diabetes development, and to promote health education.

Keywords

Diabetes Nurse Occupational health National health insurance Cohort study

Background

Nurses work on the front lines in the medical industry and account for 45.2 % of all professional medical personnel in Taiwan [1]. Numerous medical orders and procedures rely on the work of nurses; therefore, nursing care is highly correlated with care quality levels and with patient treatment outcomes, and nurses play a crucial role in the medical industry.

Ongoing care services are essential to the medical industry. Shift work creates certain occupational problems for nurses [2, 3]. Relevant studies have shown that in addition to causing an increasing number of accidents [4] and higher rates of disease and cancer development [5], engagement in shift work increases one’s likelihood of developing metabolic diseases [6, 7]. Previous studies have revealed that individuals working in occupations that involve shift work show higher risks of developing diabetes compared with those who do not work shifts [810].

Diabetes is one of the most common chronic illnesses worldwide. Statistics [11] show that approximately 366 million people worldwide were diagnosed with diabetes in 2011. This number is estimated to increase to 552 million by 2030, accounting for 4.4 % of the global population. In the United States, research has been conducted on the health status of 67,420 nurses from 1976 to 1996, and the results show that 7,401 (11 %) of the nurses were diagnosed with type 2 diabetes mellitus (DM) [12]. Since 2003, diabetes has ranked third among the top 10 causes of death among women in Taiwan [13]. Nurses are exposed to an occupational environment that may be detrimental to their health, which may affect the quality of medical care. The present study compares type 2 DM development risk levels among female nurses to those of the general female citizen population to further identify influencing factors. These data may serve as a foundation for future discussions on occupational health in relation to health promotion, prevention and protection.

Methods

Study design

A retrospective and longitudinal method was adopted in this study, and data were sourced from the National Health Insurance Research Database. To comply with privacy measures, personal information was removed from the collected data.

The Taiwanese government created a compulsory National Health Insurance (NHI) system in 1995, a governmental insurance system that all citizens are mandated to be insured under. Since the end of 2012, the NHI coverage rate reached to as high as 99.85 % [14]. The NHI covers costs for outpatient procedures; emergency procedures; and inpatient prescriptions, treatments, and examinations. The NHI database details all medical claims records for the insured, including treatments for chronic illnesses such as diabetes [15, 16].

Data sources and study participants

Data were sourced from the Longitudinal Health Insurance Research Database of 2000 published by the NHI, which included one million population randomly selected to be representative of whole population in Taiwan and a sample of nurses was selected from the nationwide Registry for Medical Personnel published by the NHI. We used female nurses and female non-nurses as the study participants. Nurses were defined as the nurses were listed in the Registry for Medical Personnel before December 31, 2000. Non-nurses were defined as the participants who had not registered as a licensed medical professional, such as physicians, dentists, physical therapists, nutritionists, and so on before the end of study observation. Participants younger than 20 years and older than 90 years and those diagnosed with type 2 DM prior to December 31, 2000 were excluded. Male nurses were excluded from the study, as most nurses in Taiwan are female (98.92 %) [17]. A total of 374,173 participants were selected, 70,675 of whom were nurses and 303,498 of whom were female non-nurses.

To objectively compare diabetes development risks among female nurses and female non-nurses, 1:1 propensity score matching was used to control for selection bias, and participants with similar characteristics and health conditions were selected from the two groups. After propensity score matching, we assigned 55,835 nurses to the observation group and 55,835 non-nurses to the control group (Table 1). Patterns of diabetes development were monitored until December 31, 2009, covering an average of 9.68 ± 1.06 years (9.72 ± 0.92 and 9.64 ± 1.19 y for nurses and non-nurses, respectively).
Table 1

Participants demographics before and after propensity score (PS) matching

Variables

Before PS Matching

After PS Matching (1:1)

Total

Non-nurses

Nurse

p -value

Total

Non-nurses

Nurse

p -value

N

%

N

%

N

%

 

N

%

N

%

N

%

 

Total participants

374173

100.00

303498

81.11

70675

18.89

 

111670

100.00

55835

50.00

55835

50.00

 

Age

       

<0.001

      

1.000

 

<25

59213

15.83

39267

12.94

19946

28.22

 

24912

22.31

12456

22.31

12456

22.31

 
 

25–34

107621

28.76

76758

25.29

30863

43.67

 

47271

42.33

23628

42.32

23643

42.34

 
 

35–44

88584

23.67

74351

24.50

14233

20.14

 

28221

25.27

14118

25.29

14103

25.26

 
 

45–54

54406

14.54

49631

16.35

4775

6.76

 

9550

8.55

4775

8.55

4775

8.55

 
 

55–64

32444

8.67

31771

10.47

673

0.95

 

1346

1.21

673

1.21

673

1.21

 
 

65

31905

8.53

31720

10.45

185

0.26

 

370

0.33

185

0.33

185

0.33

 

Average age (Mean, Std)

40.13

15.05

42.20

15.48

31.23

8.48

 

32.79

8.97

33.04

9.10

32.54

8.83

 

Monthly salary(NT$)

      

<0.001

      

1.000

 

Low-income household

1326

0.35

1312

0.43

14

0.02

 

28

0.03

14

0.03

14

0.03

 
 

17280

47252

12.63

42573

14.03

4679

6.62

 

9358

8.38

4679

8.38

4679

8.38

 
 

17281 ~ 22800

141273

37.76

134297

44.25

6976

9.87

 

13952

12.49

6976

12.49

6976

12.49

 
 

22801 ~ 28800

71049

18.99

61248

20.18

9801

13.87

 

19602

17.55

9801

17.55

9801

17.55

 
 

28801 ~ 36300

34972

9.35

23113

7.62

11859

16.78

 

20061

17.96

10023

17.95

10038

17.98

 
 

36301 ~ 45800

44721

11.95

20443

6.74

24278

34.35

 

27366

24.51

13680

24.50

13686

24.51

 
 

45801 ~ 57800

24273

6.49

14628

4.82

9645

13.65

 

16136

14.45

8068

14.45

8068

14.45

 
 

57801

9291

2.48

5868

1.93

3423

4.84

 

5167

4.63

2594

4.65

2573

4.61

 
 

Missing data

16

 

16

           

CCI

      

<0.001

      

0.980

 

0

93747

25.05

76960

25.36

16787

23.75

 

28218

25.27

14109

25.27

14109

25.27

 
 

1 ~ 3

127818

34.16

98810

32.56

29008

41.04

 

43511

38.96

21796

39.04

21715

38.89

 
 

4 ~ 6

87823

23.47

71246

23.47

16577

23.46

 

26529

23.76

13224

23.68

13305

23.83

 
 

7 ~ 9

42956

11.48

36932

12.17

6024

8.52

 

9815

8.79

4912

8.80

4903

8.78

 
 

10

21829

5.83

19550

6.44

2279

3.22

 

3597

3.22

1794

3.21

1803

3.23

 

Average CCI(Mean, Std)

3.38

3.34

3.48

3.43

2.93

2.89

 

2.93

2.90

2.92

2.89

2.93

2.92

 

CCI, Charlson Comorbidity Index; PS, propensity score

It’s 30 New Taiwan Dollar (NT$) per US dollar

p -value was considered significant at p < 0.05

Variables description

In this study, the type 2 diabetes mellitus was defined as a primary or secondary diagnosis with ICD-9-CM: 250 or A-code: A181 and the patients had made 3 or more clinic visits or been hospitalized at least once within 365 days [18], and this study excluded other types DM patients. We categorized residence areas into 7 levels, and level 1 was the most urbanized [19]. We used the modified Charlson Comorbidity Index (CCI) to classify the severity of comorbidity [20]. The CCI involved 17 comorbidities weighted based on severity. Higher score denoted greater comorbidity. Presence of catastrophic illnesses was defined as yes or no. The catastrophic illnesses or injuries were defined by National Health Insurance Administration in Taiwan including 30 categories of major illnesses (e.g., cancer, stroke, hemophilia, type I diabetes, autoimmune diseases, end-stage renal disease etc.) for which patients were exempted from copayment and thus avoided financial hardship [21].

Data analysis

A descriptive analysis was conducted to examine demographical traits of the research population (e.g., age, monthly salary, and CCI) and to classify the participants as nurses and non-nurses. Propensity matching (PS) methods were used, and a Chi-square test was subsequently employed to compare variations in diabetes development risks for the two groups. The Cox proportional hazards model was used to discuss relative risks and influencing factors related to diabetes. Hazard ratios (HRs) and 95 % CIs were derived from Cox proportional hazards models. Poisson distribution methods were employed to examine diabetes incidence rates for 1,000 person-years for the two groups. In this study, statistic significance was set at p < 0.05.

Results

Participants demographics

The data prior to propensity matching revealed significant differences (p <0.05) between age, monthly salary, and CCI levels for the two groups (Table 1). Before propensity score matching, the average age of the nurses was 31.23 ± 8.48 years, whereas that of the non-nurses was younger by 10.97 ± 7.00 years at 42.20 ± 15.48 years. Most of the nurses (34.35 %) earned a salary of NT$ 36,301–NT$ 45,800, and the non-nurses earned NT$ 17,281–NT$ 22,800 (44.25 %) on average. The CCI scores for the nurses and non-nurses were 2.93 ± 2.89 and 3.48 ± 3.43, respectively.

After performing the propensity score matching tasks, we did not find any significant differences in terms of age, monthly salaries, residence area urbanization levels, CCI levels, and in other catastrophic illness levels between the two groups (Table 1).

Stratified analysis on the risk of diabetes for the nurses and non-nurses

In the Table 2, the results of the bivariate analysis revealed a lower incidence of diabetes among the nurses (2.68 %) compared with that of the non-nurses (3.13 %), revealing a statistically significant difference (p <0.05). After controlling for other factors, Cox proportional hazards models were used to identify the risk of diabetes for the nurses and non-nurses (Table 3). The results of the nurses showed a lower risk of developing diabetes compared with the non-nurses (Adj. HR = 0.84, 95 % CI: 0.79–0.90). For age, in the 35–44- and 45–54-year age groups, the nurses exhibited a significantly lower risk of diabetes compared with the non-nurses (Adj. HR: 0.82 and 0.75, respectively). For the income groups of less than NT$ 17,280, NT$ 22,801–NT$ 28,800, and NT$ 36,301–NT$ 45,800, nurses presented significantly lower risks of diabetes development compared with those of the non-nurses (Adj. HR: 0.65, 0.77, 0.86, respectively). Regarding urbanization variables, with the exception of participants residing in Levels 4 and 5 urbanization areas, no significant differences in diabetes development risk were found between the nurses and non-nurses (p <0.05). In less urbanized regions, nurses showed lower risks of diabetes development than non-nurses (p <0.05).
Table 2

Bivariate analysis on the incidence of diabetes

Variables

Total

Without Diabetes

Diabetes

p -value

N

%

N

%

N

%

Total participants

111670

100.00

108422

97.09

3248

2.91

 

Nurses or non-nurses

      

<0.001

 

Non-nurses

55835

50.00

54085

96.87

1750

3.13

 
 

Nurses

55835

50.00

54337

97.32

1498

2.68

 

Age

       

<0.001

 

<25

24912

22.31

24695

99.13

217

0.87

 
 

25–34

47271

42.33

46626

98.64

645

1.36

 
 

35–44

28221

25.27

27085

95.97

1136

4.03

 
 

45–54

9550

8.55

8562

89.65

988

10.35

 
 

55–64

1346

1.21

1149

85.36

197

14.64

 
 

65

370

0.33

305

82.43

65

17.57

 

Average age (Mean, Std)

32.79

8.97

32.52

8.78

41.80

10.61

 

Monthly salary(NT$)

      

<0.001

 

17280

9386

8.41

9087

96.81

299

3.19

 
 

17281 ~ 22800

13952

12.49

13558

97.18

394

2.82

 
 

22801 ~ 28800

19602

17.55

19117

97.53

485

2.47

 
 

28801 ~ 36300

20061

17.96

19626

97.83

435

2.17

 
 

36301 ~ 45800

27366

24.51

26466

96.71

900

3.29

 
 

45801 ~ 57800

16136

14.45

15660

97.05

476

2.95

 
 

57801

5167

4.63

4908

94.99

259

5.01

 

Urbanization of residence

      

0.662

 

Level 1

42449

38.01

41210

97.08

1239

2.92

 
 

Level 2 & 3

52585

47.09

51079

97.14

1506

2.86

 
 

Level 4 & 5

12212

10.94

11849

97.03

363

2.97

 
 

Level 6 & 7

4424

3.96

4284

96.84

140

3.16

 

Other catastrophic illnesses

      

<0.001

 

No

109183

97.77

106068

97.15

3115

2.85

 
 

Yes

2487

2.23

2354

94.65

133

5.35

 

CCI

      

<0.001

 

0

15926

14.26

15894

99.80

32

0.20

 
 

1 ~ 3

44302

39.67

43328

97.80

974

2.20

 
 

4 ~ 6

31181

27.92

30138

96.66

1043

3.34

 
 

7 ~ 9

14076

12.60

13342

94.79

734

5.21

 
 

10

6185

5.54

5720

92.48

465

7.52

 

Average CCI (Mean, Std)

3.75

3.16

3.69

3.13

5.71

3.48

 

CCI, Charlson Comorbidity Index; HR, hazard ratio; CI, confidence interval

It’s 30 New Taiwan Dollar (NT$) per US dollar

Urbanization level of residence area (overall 7 levels; Level 1 was the most urbanized)

p -value was considered significant at p < 0.05

Table 3

Stratified Cox proportional hazard model analysis on the risk of diabetes for the nurses and non-nurses

Variables

Non-nurses

Nurses

Adj. HR*

(Nurse:GP)

95 % CI

p -value

Total

Diabetes (N)

Diabetes (%)

Total

Diabetes (N)

Diabetes (%)

Total

55835

1750

3.13

55835

1498

2.68

0.84

0.79

0.90

<0.001

Age(y/o)

          
 

<35

36084

434

2.23

36099

428

2.24

0.97

0.85

1.11

0.628

 

35–44

14118

617

4.37

14103

519

3.68

0.82

0.73

0.92

<0.001

 

45–54

4775

563

11.79

4775

425

8.90

0.75

0.66

0.85

<0.001

 

55–64

673

104

15.45

673

93

13.82

0.85

0.64

1.13

0.260

 

65

185

32

17.30

185

33

17.84

0.98

0.60

1.62

0.943

Monthly salary(NT$)

          
 

17280

4693

176

3.75

4693

123

2.62

0.65

0.52

0.82

<0.001

 

17281 ~ 22800

6976

211

3.02

6976

183

2.62

0.84

0.69

1.03

0.089

 

22801 ~ 28800

9801

273

2.79

9801

212

2.16

0.77

0.64

0.92

0.004

 

28801 ~ 36300

10023

218

2.17

10038

217

2.16

0.97

0.81

1.18

0.779

 

36301 ~ 45800

13680

479

3.50

13686

421

3.08

0.86

0.76

0.99

0.030

 

45801 ~ 57800

8068

251

3.11

8068

225

2.79

0.93

0.78

1.12

0.433

 

57801

2594

142

5.47

2573

117

4.55

0.80

0.63

1.03

0.080

Urbanization of residence

 

Level 1

22883

695

3.04

19566

544

2.78

0.86

0.76

0.96

0.006

 

Level 2 & 3

25499

804

3.15

27086

702

2.59

0.84

0.76

0.93

<0.001

 

Level 4 & 5

5544

181

3.26

6668

182

2.73

0.85

0.69

1.05

0.133

 

Level 6 & 7

1909

70

3.67

2515

70

2.78

0.71

0.50

1.00

0.050

Other catastrophic illnesses

 

No

54530

1680

3.08

54653

1435

2.63

0.84

0.78

0.90

<0.001

 

Yes

1305

70

5.36

1182

63

5.33

0.93

0.66

1.31

0.667

CCI

 

3

30433

552

2.70

29795

454

2.10

0.82

0.73

0.93

0.002

 

4 ~ 6

15428

551

3.57

15753

492

3.12

0.87

0.77

0.98

0.026

 

7 ~ 9

6912

389

5.63

7164

345

4.82

0.85

0.74

0.99

0.030

 

10

3062

258

8.43

3123

207

6.63

0.80

0.66

0.96

0.015

*The stratified Cox proportional hazards models have controlled for age, monthly salary, urbanization of residence, other catastrophic illnesses, CCI

CCI, Charlson Comorbidity Index; HR, hazard ratio; CI, confidence interval

It’s 30 New Taiwan Dollar (NT$) per US dollar

p -value was considered significant at p < 0.05

An analysis on the comorbidity of other catastrophic illnesses indicated that risks of diabetes development facing those nurses who did not have other catastrophic illnesses were significantly lower than those of non-nurses (Adj. HR: 0.84; p <0.05). While risks of diabetes development among the nurses with catastrophic illnesses were lower than those for the non-nurses, the results were non-significant (p <0.05). The results of the CCI analysis show that the nurses presented significantly lower susceptibility to diabetes development overall compared with the non-nurses (p <0.05).

Relative factors and the incidence of diabetes among nurses

The analysis results presented in Table 4 show that age and CCI serves as critical factors that influence diabetes development risks among nurses. Regarding age variables, a 10-year period was used as an interval to create age groups. The older nurses presented relatively higher risks of diabetes development compared with the nurses of less than 25 years (Adj. HR: 1.56–16.85). Nurses who were older than 65 years of age showed a 16.85-fold higher risk of developing diabetes compared with nurses who were younger than 25 years of age (95 % CI: 11.47–24.75).
Table 4

Relative factors and the incidence risk of diabetes among nurses

Variables

Unadj.

HR

P-value

Adj.

HR

95 % CI

p -value

Age

 

<25 (reference)

      
 

25–34

1.57

<0.001

1.56

1.30

1.87

<0.001

 

35–44

4.52

<0.001

4.19

3.50

5.01

<0.001

 

45–54

11.29

<0.001

9.59

7.97

11.55

<0.001

 

55–64

18.10

<0.001

13.85

10.67

17.99

<0.001

 

65

25.34

<0.001

16.85

11.47

24.75

<0.001

Monthly salary(NT$)

 

17280(reference)

      
 

17281 ~ 22800

1.00

0.991

1.23

0.98

1.55

0.077

 

22801 ~ 28800

0.83

0.090

1.03

0.82

1.28

0.830

 

28801 ~ 36300

0.76

0.015

1.11

0.89

1.38

0.350

 

36301 ~ 45800

0.81

0.035

1.06

0.87

1.29

0.588

 

45801 ~ 57800

0.92

0.449

0.98

0.79

1.23

0.884

 

57801

1.42

0.006

1.08

0.84

1.39

0.537

Urbanization of residence

 

Level 1(reference)

      
 

Level 2 & 3

0.98

0.672

0.97

0.87

1.08

0.572

 

Level 4 & 5

1.05

0.545

0.97

0.83

1.14

0.719

 

Level 6 & 7

1.11

0.407

0.91

0.72

1.16

0.441

Other catastrophic illnesses

 

No(reference)

      
 

Yes

2.18

<0.001

1.24

0.97

1.59

0.090

CCI

 

0 (reference)

      
 

1 ~ 3

12.75

<0.001

12.25

6.74

22.28

<0.001

 

4 ~ 6

21.44

<0.001

18.66

10.27

33.90

<0.001

 

7 ~ 9

34.13

<0.001

24.85

13.64

45.30

<0.001

 

10

48.23

<0.001

28.48

15.51

52.29

<0.001

CCI, Charlson Comorbidity Index; HR, hazard ratio; CI, confidence interval

It’s 30 New Taiwan Dollar (NT$) per US dollar

Urbanization level of residence area (overall 7 levels; Level 1 was the most urbanized)

p -value was considered significant at p < 0.05

CCI significantly influences diabetes development risks among nurses. The analysis results indicate that those nurses with a higher CCI were at a higher risk of developing diabetes than the reference group (CCI = 0). Those nurses with a CCI of 10 presented 28.48-fold higher relative risks of diabetes development than the reference group (95 % CI: 15.51–52.29). The research results shown in Table 5 indicate that diabetes incidence rates per 1,000 person-years for the nurses were lower than those of the non-nurses (2.76 ‰ vs. 3.25 ‰). The analysis results on the various variables reveal that with the exception of the 25-year age group, the incidence rate of diabetes per 1,000 person-years for nurses of all of the age groups was lower than that of the non-nurses.
Table 5

The incidence rate of diabetes per 1000 person-years

Variables

Non-nurses

Nurses

p -value

Diabetes (N)

Incidence rate(%)

Diabetes (N)

Incidence rate(%)

Total participants

1750

3.25

1498

2.76

<0.001

Age

 

<25

104

0.87

113

0.94

0.574

 

25–34

330

1.44

315

1.36

0.492

 

35–44

617

4.53

519

3.78

0.003

 

45–54

563

12.63

425

9.41

<0.001

 

55–64

104

17.25

93

14.97

0.322

 

65

32

21.99

33

20.62

0.794

Average age (Mean, Std)

48.31

10.43

46.98

10.80

<0.001

Monthly salary(NT$)

 

17280

176

4.07

123

2.71

<0.001

 

17281 ~ 22800

211

3.14

183

2.70

0.139

 

22801 ~ 28800

273

2.89

212

2.23

0.005

 

28801 ~ 36300

218

2.25

217

2.23

0.924

 

36301 ~ 45800

479

3.61

421

3.16

0.045

 

45801 ~ 57800

251

3.20

225

2.86

0.221

 

57801

142

5.68

117

4.68

0.120

Urbanization of residence

 

Level 1

695

3.14

544

2.85

0.094

 

Level 2 & 3

804

3.28

702

2.67

<0.001

 

Level 4 & 5

181

3.40

182

2.82

0.077

 

Level 6 & 7

70

3.81

70

2.87

0.093

Other catastrophic illnesses

 

No

1680

3.19

1435

2.70

<0.001

 

Yes

70

5.72

63

5.63

0.928

CCI

 

0

22

0.26

10

0.14

0.107

 

1 ~ 3

530

2.52

444

2.01

<0.001

 

4 ~ 6

551

3.69

492

3.22

0.028

 

7 ~ 9

389

5.89

345

5.01

0.029

 

10

258

9.06

207

7.01

0.006

CCI, Charlson Comorbidity Index

It’s 30 New Taiwan Dollar (NT$) per US dollar

Urbanization level of residence area (overall 7 levels; Level 1 was the most urbanized)

p -value was considered significant at p < 0.05

Discussion

After the research population was collected from the NHI database, 1:1 propensity score matching was employed. The results of the bivariate analysis shown in Table 2 indicate that the nurses presented a lower risk of diabetes development than the non-nurses (2.68 % vs. 3.13 %), which is consistent with that of the Cox proportional hazards model (Table 3 and Fig. 1; Adj. HR: 0.83, 95 % CI: 0.78–0.89).
Fig. 1

Relative risk of diabetes in nurses and non-nurses

Previous studies [810] have determined that individuals who work in professions that require shift work present higher risks of developing diabetes. After propensity score matching, our nurses cohort and non-nurses control group were similar in terms of demographics, socioeconomic status, and health conditions. However, the nurses showed lower risks of developing diabetes than the non-nurses, and this may be attributed to nurses’ medical knowledge and educational training. Furthermore, nurses are assume health promotion and education responsibilities [22] and are thus likely to live healthy lifestyles and to invest in their long-term health. This phenomenon is known as the healthy worker effect [23, 24]. Nurses must be in excellent health to achieve effective performance; therefore, nurses are generally healthier than non-nurses.

The aforementioned results may be correlated with knowledge, attitudes, and practice (KAP) theory principles [25, 26]. Self-care levels depend on patient behaviors, and a patient’s knowledge influences his or her attitudes, thereby affecting his or her practices. Acquiring correct knowledge about a disease and adopting positive and proactive attitudes are essential for motivating self-care behaviors, which directly or indirectly affect health outcomes. Nurses are equipped with comprehensive medical knowledge and thus possess a favorable view of personal health and diseases and a positive attitude toward medical care, resulting in superior self-care [27]. However, further study is needed to examine the effect of KAP theory on the nurses’ incidence risk of developing diabetes.

The results presented in Tables 3 and 4 show that for the entire sample population, age and CCI variables most heavily influenced diabetes development risks. The older participants presented higher risks of diabetes development than the reference group (<25 y), complementing the results of previous studies [2830], and this shows that glucose tolerance levels decrease with age; therefore, diabetes development risks increase rapidly among individuals who are older than 45 years of age. As shown in Table 5, a rapid increase in the incidence rate of diabetes per 1,000 person-years was observed among both nurses and non-nurses of 45 years of age and older. As shown in Tables 3 and 4, a higher CCI involves an increased relative risk of diabetes development, complementing the results of Huang [31] and Monami et al. [32]. Thus, CCI serves as a critical variable for predicting diabetes development risks.

Study limitations

There are several limitations to our analyses. According to the International Statistical Classification of Diseases (ICD), DM diagnosis is based on an ICD-9 diagnosis code. Therefore, clinical diagnostic data could not be acquired and verified. To optimize the accuracy of this study while compensating for this limitation, diabetes occurrence was identified when patients visited an outpatient department three times or when they were hospitalized more than once within 365 days of receiving a primary or secondary diabetes diagnosis (ICD-9-CM: 250 or A-code: A181) [17]. Some risk factors are not present in analysis. For instance, information on lifestyle, health behaviors and clinical testing data were not available and thus could not be used in variable analyses. So, we used the propensity score matching to control for selection bias. The propensity score adjustment is an important statistical technique to reduce the bias from confounding variables in observational studies and mimic the results of a randomized controlled trial [33]. In addition, the long follow-up and national design provided adequate power.

Conclusion

This study is the first to use a nationwide database to compare risks of diabetes development among female nurses and female non-nurses. The results show that nurses present a lower risk of developing diabetes than non-nurses. This result may be attributable to the fact that nurses possess superior medical knowledge and thus have lower incidence risk of developing diabetes.

Abbreviations

CCI, Charlson Comorbidity Index; CI, confidence interval; DM, diabetes mellitus; HR, hazard ratio; ICD, International Statistical Classification of Diseases; KAP, knowledge, attitudes, and practice; NHI, National Health Insurance; NT$, New Taiwan Dollar; PS, propensity score.

Declarations

Acknowledgments

We are grateful for use of the National Health Insurance Research Database provided by the National Health Research Institutes. The interpretations and conclusions contained herein do not represent those of the Ministry of Health and Welfare, Taiwan, R.O.C.

Funding

This study was supported by the grant (CMU102-ASIA-12) from China Medical University and Asia University as well as the grant (DOH 10216) from Ministry of Health and Welfare.

Availability of data and materials

Data are available from the National Health Research Institutes (NHRI), Taiwan. All interested researchers can obtain the databases published and managed by the NHRI. All researchers are allowed to use the databases for their studies if they are interested in using the data. Before using the databases for research, all studies should get the IRB permission.

Authors’ contributions

HLH and WCT drafted the manuscript. WCT and PTK designed the study. CCP, SMW, PTK and WYC collected data. HLH, PTK and WCT were responsible for study conceptualization and developing the analytical plan. All authors read and approved the final manuscript.

Competing interests

The authors declare that they have no competing interests.

Consent for publication

Not applicable.

Ethics statement

The institutional review board of China Medical University approved this study (IRB No.: CMUH 20130326C).

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Authors’ Affiliations

(1)
Department of Aged Welfare & Social Work, Toko University
(2)
Department of Public Health and Department of Health Services Administration, China Medical University
(3)
Department of Urology, Hengchun Tourism Hospital, Ministry of Health and Welfare
(4)
Department of Healthcare Administration, Asia University
(5)
Department of Health Services Administration, China Medical University

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Copyright

© Huang et al. 2016

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