Baseline characteristics.
Participants’ basic characteristics are shown in Table 1. The middle-aged and elderly groups were matched by the propensity score of 3,957 people. According to their income level, they were divided into quartiles comprising 921 people in the low group, 999 people in the low-mid group, 1012 people in the high-mid group, and 1025 people in the high group.
Table 1
Baseline characteristics by household income level after propensity score matching.
| Middle-aged group | Elderly group |
| Low | Low-mid | High-mid | High | P-value | Low | Low-mid | High-mid | High | P-value |
| (N = 921) | (N = 999) | (N = 1012) | (N = 1025) | | (N = 921) | (N = 999) | (N = 1012) | (N = 1025) | |
Age | 44.0 ± 12.6 | 44.3 ± 12.5 | 43.9 ± 12.4 | 44.8 ± 12.6 | 0.194 | 71.9 ± 4.6 | 72.0 ± 4.8 | 71.7 ± 4.7 | 71.6 ± 4.7 | 0.047 |
Sex | | | | | 0.817 | | | | | 0.817 |
Male | 415 (45.1%) | 436 (43.6%) | 460 (45.5%) | 450 (43.9%) | | 415 (45.1%) | 436 (43.6%) | 460 (45.5%) | 450 (43.9%) | |
Female | 506 (54.9%) | 563 (56.4%) | 552 (54.5%) | 575 (56.1%) | | 506 (54.9%) | 563 (56.4%) | 552 (54.5%) | 575 (56.1%) | |
SBP | 116.4 ± 15.6 | 116.3 ± 15.7 | 115.8 ± 15.4 | 115.1 ± 15.8 | 0.063 | 128.9 ± 17.0 | 129.2 ± 18.1 | 127.7 ± 16.5 | 128.4 ± 17.3 | 0.236 |
DBP | 75.9 ± 10.4 | 75.9 ± 10.3 | 76.1 ± 10.5 | 75.5 ± 10.4 | 0.535 | 73.5 ± 10.1 | 72.8 ± 10.4 | 72.8 ± 9.7 | 73.2 ± 9.5 | 0.635 |
WC | 81.0 ± 10.0 | 80.8 ± 9.6 | 80.7 ± 9.6 | 79.8 ± 9.6 | 0.005 | 84.5 ± 9.2 | 83.9 ± 9.0 | 84.6 ± 8.9 | 84.3 ± 8.9 | 0.880 |
BMI | 23.9 ± 3.7 | 23.9 ± 3.4 | 23.8 ± 3.3 | 23.5 ± 3.3 | 0.01 | 24.0 ± 3.2 | 23.9 ± 3.1 | 24.1 ± 3.0 | 24.1 ± 3.1 | 0.127 |
Total cholesterol | 188.6 ± 35.5 | 191.1 ± 36.8 | 189.7 ± 34.7 | 190.6 ± 35.2 | 0.38 | 189.0 ± 38.9 | 187.9 ± 36.4 | 188.3 ± 38.1 | 185.8 ± 35.4 | 0.084 |
MDRD eGFR | 97.0 ± 18.8 | 96.6 ± 17.4 | 96.3 ± 18.4 | 94.8 ± 17.2 | 0.008 | 83.6 ± 17.5 | 82.9 ± 18.0 | 83.3 ± 18.1 | 81.7 ± 18.1 | 0.034 |
Current smoker | 244 (26.5%) | 227 (22.7%) | 222 (21.9%) | 175 (17.1%) | < 0.001 | 123 (13.4%) | 101 (10.1%) | 111 (11.0%) | 73 (7.1%) | 0.000 |
Education | | | | | 0.000 | | | | | 0.000 |
Elementary school | 183 (19.9%) | 143 (14.3%) | 88 (8.7%) | 55 (5.4%) | | 680 (73.8%) | 698 (69.9%) | 585 (57.8%) | 443 (43.2%) | |
Middle school | 120 (13.0%) | 101 (10.1%) | 85 (8.4%) | 58 (5.7%) | | 107 (11.6%) | 138 (13.8%) | 165 (16.3%) | 131 (12.8%) | |
High school | 393 (42.7%) | 411 (41.1%) | 395 (39.0%) | 357 (34.8%) | | 102 (11.1%) | 127 (12.7%) | 188 (18.6%) | 254 (24.8%) | |
College | 225 (24.4%) | 344 (34.4%) | 444 (43.9%) | 555 (54.1%) | | 32 (3.5%) | 36 (3.6%) | 74 (7.3%) | 197 (19.2%) | |
SBP, Systolic Blood Pressure; DBP, Diastolic Blood Pressure; WC, Weight Change; BMI, Body Mass Index; MDRD, Modification of Diet in Renal Disease; eGFR estimated glomerular filtration rate. |
In the middle age group, no differences in systolic and diastolic blood pressure according to income level were found. Abdominal circumference and BMI tended to be higher among those with lower income levels. Further, the Modification of Diet in Renal Disease (MDRD) eGFR and proportion of smokers was higher among those with lower income levels. Regarding educational level, higher income levels were significantly positively associated with university education, and negatively associated with elementary school education.
In the elderly age group, no significant differences in blood pressure, abdominal circumference, BMI, and total cholesterol level were found by income level. Lower income levels were associated with higher MDRD eGFR. Further, educational level and smoking rate showed similar trends by income level, as in the middle-aged group.
Prevalence of chronic disease and medical service needs.
In the middle age group, lower income levels were associated with a higher prevalence of hypertension, diabetes, and metabolic syndrome. The prevalence of hypertension was 17.5% and 24.0% in high- and low-income groups respectively. Additionally, 6.3% and 10.0% of patients in the high- and low-income group were diagnosed with diabetes, respectively. However, the prevalence of CKD did not differ between groups. Regarding the lack of access to necessary medical services due to economic reasons, 0.5% and 7.6% of those in the high- and low-income groups, respectively did not receive essential medical services owing to economic reasons (Table 2). However, no statistically significant difference was observed for this variable.
Table 2
Prevalence of chronic disease and medical service needs by household incomes between the age groups.
| Low | Low-mid | High-mid | High | P-value |
Middle-age group (N = 3957) | (N = 921) | (N = 999) | (N = 1012) | (N = 1025) | |
Chronic disease | | | | | |
Hypertension | 221 (24.0%) | 209 (20.9%) | 214 (21.1%) | 179 (17.5%) | 0.012 |
DM | 92 (10.0%) | 79 (7.9%) | 66 (6.5%) | 65 (6.3%) | 0.013 |
CKD | 12 (1.3%) | 11 (1.1%) | 8 (0.8%) | 12 (1.2%) | 0.161 |
Metabolic syndrome | 133 (14.4%) | 119 (11.9%) | 128 (12.6%) | 98 (9.6%) | 0.010 |
Metabolic syndrome score | | | | | 0.002 |
0 | 368 (40.0%) | 415 (41.5%) | 421 (41.6%) | 496 (48.4%) | |
1 | 255 (27.7%) | 287 (28.7%) | 271 (26.8%) | 270 (26.3%) | |
2 | 165 (17.9%) | 178 (17.8%) | 192 (19.0%) | 161 (15.7%) | |
3 | 109 (11.8%) | 95 (9.5%) | 90 (8.9%) | 74 (7.2%) | |
4 | 24 (2.6%) | 24 (2.4%) | 38 (3.8%) | 24 (2.3%) | |
Lack of access to necessary medical services owing to economic reasons | 70 (7.6%) | 25 (2.5%) | 20 (2.0%) | 5 (0.5%) | 0.730 |
Elderly group (N = 3957) | (N = 921) | (N = 999) | (N = 1012) | (N = 1025) | |
Chronic disease | | | | | |
Hypertension | 555 (60.3%) | 629 (63.0%) | 616 (60.9%) | 621 (60.6%) | 0.611 |
DM | 222 (24.1%) | 210 (21.0%) | 233 (23.0%) | 228 (22.2%) | 0.772 |
CKD | 217 (23.5%) | 205 (20.5%) | 221 (21.8%) | 220 (21.46%) | 0.499 |
Metabolic syndrome | 222 (24.1%) | 201 (20.1%) | 239 (23.6%) | 216 (21.1%) | 0.095 |
Metabolic syndrome score | | | | | 0.006 |
0 | 127 (13.8%) | 192 (19.2%) | 186 (18.4%) | 185 (18.0%) | |
1 | 305 (33.1%) | 275 (27.5%) | 309 (30.5%) | 314 (30.6%) | |
2 | 267 (29.0%) | 331 (33.1%) | 278 (27.5%) | 310 (30.2%) | |
3 | 173 (18.8%) | 162 (16.2%) | 197 (19.5%) | 179 (17.5%) | |
4 | 49 (5.3%) | 39 (3.9%) | 42 (4.2%) | 37 (3.6%) | |
Lack of access to necessary medical services owing to economic reasons | 100 (10.9%) | 61 (6.1%) | 66 (6.5%) | 30 (2.9%) | < 0.001 |
DM, Diabetes Mellitus; CKD, Chronic Kidney Disease |
In the elderly age group, unlike the middle-aged group, no differences were observed across the groups in the prevalence of hypertension, diabetes, CKD, and metabolic syndrome. However, there were significant differences regarding the lack of access to necessary medical services due to economic reasons according to income level. Food safety scores in the survey showed significant differences between groups (Table 3).
Table 3
Food security questionnaire for the Korean National Health and Nutrition Examination Survey (Investigated over 65 years).
| Low | Low-mid | High-mid | High | P-value |
Age ≥ 65 years | | | | | |
1. Food security | | | | | 0.000 |
A. We were able to eat a sufficient amount and variety of food. | 303 (32.9%) | 388 (38.8%) | 468 (46.2%) | 590 (57.6%) | |
B. We were able to eat a sufficient amount of food, but not a variety of foods. | 480 (52.1%) | 524 (52.5%) | 504 (49.8%) | 418 (40.8%) | |
C. Because of a lack of money for food, food didn’t sometimes last | 103 (11.2%) | 68 (6.8%) | 30 (3.0%) | 15 (1.5%) | |
D. Because of a lack of money for food, food didn’t often last | 35 (3.8%) | 19 (1.9%) | 10 (1.0%) | 2 (0.2%) | |
2. During the last 12 months, because of a lack of money for food, how often did food not last in your household? | | | | | 0.000 |
A. Often | 31 (3.4%) | 17 (1.7%) | 11 (1.1%) | 4 (0.4%) | |
B. Sometimes | 97 (10.5%) | 87 (8.7%) | 49 (4.8%) | 23 (2.2%) | |
C. Never | 793 (86.1%) | 895 (89.6%) | 952 (94.1%) | 998 (7.4%) | |
3. During the last 12 months, because of a lack of money for food, how often have you/others in your household worried about running out food before getting money to buy more? | | | | | 0.000 |
A. Often | 109 (11.8%) | 62 (6.2%) | 35 (3.5%) | 23 (2.2%) | |
B. Sometimes | 168 (18.2%) | 165 (16.5%) | 107 (10.6%) | 61 (6.0%) | |
C. Never | 644 (69.9%) | 772 (77.3%) | 870 (86.0%) | 941 (91.8%) | |
4. During the last 12 months, because of a lack of money for food, how often were you (you/others in your household) unable to afford to eat balanced meals? | | | | | 0.000 |
A. Often | 107 (11.6%) | 107 (10.7%) | 53 (5.2%) | 29 (2.8%) | |
B. Sometimes | 177 (19.2%) | 153 (15.3%) | 130 (12.8%) | 68 (6.6%) | |
C. Never | 637 (69.2%) | 739 (74.0%) | 829 (81.9%) | 928 (0.5%) | |
5. During the last 12 months, because of a lack of money for food, have you (you/other adults in your household) ever either cut the size of your meals or skipped meals? | | | | | 0.000 |
A. Yes | 53 (5.8%) | 22 (2.2%) | 6 (0.6%) | 5 (0.5%) | |
B. No | 319 (34.6%) | 318 (31.8%) | 220 (21.7%) | 122 (11.9%) | |
C. Doesn’t know or refuses to answer | 549 (59.6%) | 659 (66.0%) | 786 (77.7%) | 898 (87.6%) | |
5 − 1. How often? | | | | | 0.000 |
A. Almost every month | 18 (2.0%) | 6 (0.6%) | 2 (0.2%) | 2 (0.2%) | |
B. Some months but not every month | 16 (1.7%) | 6 (0.6%) | 0 (0.0%) | 0 (0.0%) | |
C. Only one or two months | 19 (2.1%) | 10 (1.0%) | 4 (0.4%) | 3 (0.3%) | |
6. During the last 12 months, because of a lack of money for food, have you ever eaten less than you felt you should? | | | | | 0.000 |
A. Yes | 98 (10.6%) | 88 (8.8%) | 53 (5.2%) | 24 (2.3%) | |
B. No | 274 (29.8%) | 252 (25.2%) | 173 (17.1%) | 103 (10.0%) | |
7. During the last 12 months, because of a lack of money for food, have you ever not eaten although you were hungry? | | | | | 0.000 |
A. Yes | 52 (5.6%) | 24 (2.4%) | 12 (1.2%) | 3 (0.3%) | |
B. No | 320 (34.7%) | 316 (31.6%) | 214 (21.1%) | 124 (12.1%) | |
8. During the last 12 months, because of a lack of money for food, have you ever lost weight because you did not eat as needed? | | | | | 0.000 |
A. Yes | 43 (4.7%) | 27 (2.7%) | 10 (1.0%) | 1 (0.1%) | |
B. No | 329 (35.7%) | 313 (31.3%) | 216 (21.3%) | 126 (12.3%) | |
9. During the last 12 months, because of a lack of money for food, have you (you/you or other adults in your household) ever been hungry for a whole day? | | | | | 0.000 |
A. Yes | 7 (0.8%) | 1 (0.1%) | 0 (0.0%) | 0 (0.0%) | |
B. No | 115 (12.5%) | 99 (9.9%) | 57 (5.6%) | 28 (2.7%) | |
9 − 1. How often? | | | | | 0.021 |
A. Almost every month | 1 (0.1%) | 0 (0.0%) | 0 (0.0%) | 0 (0.0%) | |
B. Some months but not every month | 2 (0.2%) | 0 (0.0%) | 0 (0.0%) | 0 (0.0%) | |
C. Only one or two months | 4 (0.4%) | 1 (0.1%) | 0 (0.0%) | 0 (0.0%) | |
10. During the last 12 months, because of a lack of or being frugal about money for food, how often have you fed your child/children with only one or two kinds of low-cost food? | | | | | 0.000 |
A. Often | 9 (1.0%) | 5 (0.5%) | 7 (0.7%) | 3 (0.3%) | |
B. Sometimes | 10 (1.1%) | 14 (1.4%) | 13 (1.3%) | 7 (0.7%) | |
C. Never | 57 (6.2%) | 58 (5.8%) | 92 (9.1%) | 179 (17.5%) | |
11. During the last 12 months, because of a lack of money, how often did you not feed your child/children a balanced meal? | | | | | 0.000 |
A. Often | 10 (1.1%) | 3 (0.3%) | 9 (0.9%) | 3 (0.3%) | |
B. Sometimes | 11 (1.2%) | 14 (1.4%) | 8 (0.8%) | 14 (1.4%) | |
C. Never | 55 (6.0%) | 60 (6.0%) | 95 (9.4%) | 172 (16.8%) | |
12. During the last 12 months, because of a lack of money, how often did you not feed your child/children as needed? | | | | | 0.000 |
A. Often | 7 (0.8%) | 5 (0.5%) | 5 (0.5%) | 1 (0.1%) | |
B. Sometimes | 12 (1.3%) | 7 (0.7%) | 11 (1.1%) | 8 (0.8%) | |
C. Never | 57 (6.2%) | 65 (6.5%) | 96 (9.5%) | 180 (17.6%) | |
13. During the last 12 months, because of a lack of money, have you ever cut the size of your (child’s/children’s) meals? | | | | | 0.612 |
A. Yes | 3 (0.3%) | 0 (0.0%) | 2 (0.2%) | 2 (0.2%) | |
B. No | 22 (2.4%) | 25 (2.5%) | 22 (2.2%) | 18 (1.8%) | |
14. During the last 12 months, because of a lack of money, have your child/children ever skipped meals? | | | | | 0.461 |
A. Yes | 0 (0.0%) | 0 (0.0%) | 1 (0.1%) | 2 (0.2%) | |
B. No | 25 (2.7%) | 25 (2.5%) | 23 (2.3%) | 18 (1.8%) | |
14 − 1. How often? | | | | | |
A. Almost every month | | | | | |
B. Some months but not every month | | | | | |
C. Only one or two months | | | | | |
15. During the last 12 months, because of a lack of money, have your child/children ever not eaten although they were hungry? | | | | | 0.967 |
A. Yes | 2 (0.2%) | 2 (0.2%) | 2 (0.2%) | 2 (0.2%) | |
B. No | 23 (2.5%) | 23 (2.3%) | 22 (2.2%) | 18 (1.8%) | |
16. During the last 12 months, because of a lack of money, have your child/children ever been hungry for a whole day? | | | | | |
A. Yes | | | | | |
B. No | | | | | |
Total score of food security | 1.1 ± 1.9 | 0.8 ± 1.5 | 0.5 ± 1.2 | 0.3 ± 0.9 | 0.000 |
Four levels of food security | | | | | 0.000 |
I. Food secure | 762 (82.7%) | 875 (87.6%) | 935 (92.4%) | 982 (95.8%) | |
II. Food insecure without hunger | 119 (12.9%) | 111 (11.1%) | 72 (7.1%) | 42 (4.1%) | |
III. Moderate food insecure with hunger | 37 (4.0%) | 13 (1.3%) | 5 (0.5%) | 1 (0.1%) | |
IV. Severe food insecure with hunger | 3 (0.3%) | 0 (0.0%) | 0 (0.0%) | 0 (0.0%) | |
All of the food security questions were recoded into two categories [(often/sometimes vs. never) or (yes vs. no) or (almost every month/some months but not every month vs. only one or two months)]. Each item was given a score of 1, if the answer pointed often/sometimes, yes or almost every month/some months but not every month, or 0 for the rest responses. An additive total score was created and was classified into four levels of food security: 1) food secure [score: 0–2 (households with children); 0–2 (households without children)]; 2) food insecure without hunger [score: 3–7 (households with children; 3–5 (households without children)]; 3) moderate food insecure with hunger (8–12; 6–8); and 4) severe food insecure with hunger (13–18; 9–10) |
Table 4
A. Effect of income level on the prevalence of hypertension.
| Model 1 | Model 2 | Model 3 | Model 4 |
Under 65 years of age | Odds ratio | 95% CI | Odds ratio | 95% CI | Odds ratio | 95% CI | Odds ratio | 95% CI |
Income (ref. high income level) | | | | | | | | |
Low | 1.49 | 1.19 ~ 1.86 | 1.55 | 1.23 ~ 1.94 | 1.15 | 0.91 ~ 1.46 | 1.12 | 0.82 ~ 1.52 |
Low–mid | 1.25 | 1.00 ~ 1.56 | 1.26 | 1.01 ~ 1.58 | 1.01 | 0.80 ~ 1.27 | 0.93 | 0.69 ~ 1.24 |
High–mid | 1.26 | 1.01 ~ 1.58 | 1.27 | 1.02 ~ 1.59 | 1.12 | 0.89 ~ 1.41 | 1.05 | 0.79 ~ 1.41 |
Food security (ref. Food secure) | | | 0.78 | 0.56 ~ 1.07 | 0.72 | 0.51 ~ 0.99 | 0.76 | 0.50 ~ 1.15 |
Over 65 years of age | Odds ratio | 95% CI | Odds ratio | 95% CI | Odds ratio | 95% CI | Odds ratio | 95% CI |
Income (ref. high income level) | | | | | | | | |
Low | 0.98 | 0.82 ~ 1.18 | 0.98 | 0.81 ~ 1.17 | 0.88 | 0.73 ~ 1.07 | 0.85 | 0.68 ~ 1.06 |
Low–mid | 1.10 | 0.92 ~ 1.32 | 1.10 | 0.91 ~ 1.31 | 1.00 | 0.83 ~ 1.21 | 1.05 | 0.84 ~ 1.30 |
High - mid | 1.01 | 0.84 ~ 1.20 | 1.01 | 0.84 ~ 1.20 | 0.95 | 0.79 ~ 1.14 | 0.98 | 0.79 ~ 1.03 |
Food security (ref. Food secure) | | | 1.05 | 0.84 ~ 1.30 | 1.00 | 0.81 ~ 0.93 | 0.90 | 0.70 ~ 1.16 |
Regression analysis based on income level.
In the middle age group, the relative risk of hypertension according to income level was 1.49 times (95% CI 1.19–1.86) and 1.55 times (95% CI 1.23–1.94) higher in the low-income group, compared with that in the high-income group in Models 1 and 2, respectively (Table 4A). However, since there was no significant increase in risk in Models 3 and 4, the effect of education level and food safety on the prevalence of hypertension could not be confirmed. The relative risk of diabetes according to income level was 1.63 times (95% CI 1.17–2.28) and 1.61 times (95% CI 1.15–2.27) higher in the low-income group, compared with that in the high-income group in Model 1 and 2, respectively; however, the effect of education level and food safety could not be confirmed (Table 4B). There was no increase in the relative risk of CKD in any of the Models.
In the elderly age group, no increase in the relative risk of hypertension or diabetes in Model 1–4 was observed. The effect of income level, education level, and food security on the prevalence of hypertension and diabetes could not be identified. However, the relative risk of CKD due to food insecurity increased by 1.33 times (95% CI 1.00–1.74) and 1.34 times (95% CI 1.01–1.75) in Models 2 and 3, respectively. (Table 4C).