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The prevalence of obesity has grown rapidly in the Chinese population over the past decade. Between the periods of 2002 and 2012, according to the China Nutrition and Health Survey (CNHS), the obesity rate increased from 7.1% to 11.9% in Chinese adults[1,2]. According to a recent estimate, 0.13 billion adults are obese [body mass index (BMI) ≥ 28 kg/m2] in China[3]. Compared with the general obesity rate, the prevalence of abdominal obesity in the Chinese population was higher. Approximately 26.0% men [waist circumference (WC) ≥ 90 cm] and 25.3% women (WC ≥ 85 cm) adults had abdominal obesity in 2012. The age-adjusted prevalence of abdominal obesity increased by 42.1% among men and 26.5% among women from 2002 to 2012[4].
High BMI has been identified as the fourth leading risk factor for global death, following high systolic blood pressure, smoking, and high fasting plasma glucose; it was reported to cause 4.72 million deaths and 148 million DALYs globally by a 2017 GBD study[5]. However, Asians have higher prevalence of abdominal obesity despite the relatively lower prevalence of general obesity than other races[6]. Adverse health consequences associated with obesity may be increasingly underestimated by trends in BMI alone[7]. Unfortunately, BMI does not consider the distribution of body fat, but a number of diseases and mortality are more closely related to visceral fatty tissue accumulation than overall body fatness[8–11]. Moreover, BMI has undetermined validity for use as a measure of fatness in older people, as aging is generally associated with a considerable loss in lean body mass and some increase in fat mass[12]. Accumulating evidence showed that measurement of abdominal obesity is strongly and positively associated with all-cause, CVD, and cancer mortality independent of general obesity[13,14]; it may be a better predictor for the risk of myocardial infarction[15], type 2 diabetes[16], and metabolic syndrome than others[17]. Given that abdominal obesity is widely prevalent and rapidly growing in China, few studies have evaluated WC in association with mortality in Chinese. Thus, this study aimed to determine the degree of WC prediction for all-cause mortality. Moreover, whether there are gender-specific or age-specific particularities regarding the associations among Chinese adults was investigated using the Shanxi Nutrition and Chronic Diseases Family Cohort (Shanxi Cohort).
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There were 7,007 participants aged 18 years old and above, and complete core information was recorded at the baseline database. The mean (SD) age was 43.8 (14.2) years, and 54.5% were women. A total of 5,360 participants (2,572 males and 2,788 females) attended the follow-up survey, and 1,647 participants (620 males and 1,027 females) were lost during 2015 and 2016. Table 1 shows details of the study participants at baseline by comparing the general information between the follow-up and lost subjects. The male follow-up subjects were older and had a lower WC than their lost counterparts. The proportion of marital status and drinking significantly differed between the follow-up and lost males. The female follow-up subjects were older and had a lower height and WC than their lost counterparts. The proportion of education level, occupation, and marital status and the prevalence of hypertension significantly differed between the follow-up and lost females.
Item Male (n = 3,192) Female (n = 3,815) Follow-up Lost Statistical value* P Follow-up Lost Statistical value* P N 2,572 620 2,788 1,027 Age (Mean ± SD, years) 45.9 ± 14.0 44.2 ± 14.8 2.80 0.005 44.0 ± 13.6 38.0 ± 14.5 11.57 < 0.001 Height (Mean ± SD, cm) 167.3 ± 6.1 167.8 ± 6.9 −1.66 0.097 156.3 ± 5.9 157.4 ± 5.6 −5.32 < 0.001 Weight (Mean ± SD, kg) 65.8 ± 9.9 66.6 ± 10.0 −1.78 0.075 58.5 ± 9.2 58.7 ± 8.9 −0.69 0.490 BMI (Mean ± SD, kg/m2) 23.5 ± 3.1 23.7 ± 3.2 −1.13 0.258 24.0 ± 3.5 23.7 ± 3.3 1.98 0.048 WC (Mean ± SD, cm) 80.4 ± 9.2 81.3 ± 9.2 −2.10 0.035 76.7 ± 9.1 78.6 ± 9.9 −5.37 < 0.001 Education, N (%) 2,562 (100) 619 (100) 3.05 0.218 2,782 (100) 1,027 (100) 81.21 < 0.001 Junior high school or lower 1,888 (73.7) 440 (71.1) 2,299 (82.6) 717 (69.8) High school 513 (20.0) 129 (20.8) 383 (13.8) 223 (21.7) College or higher 161 (2.3) 50 (8.1) 100 (3.6) 87 (8.5) Occupation, N (%) 2,571 (100) 617 (100) 4.04 0.133 2,786 (100) 1,026 (100) 72.67 < 0.001 Non-manual 553 (21.5) 127 (20.6) 274 (9.8) 202 (19.7) Manual 1,616 (62.8) 373 (60.4) 864 (31.0) 244 (23.8) Others 402 (15.7) 117 (19.0) 1,648 (59.2) 580 (56.5) Marital status, N (%) 2,569 (100) 619 (100) 32.00 < 0.001 2,788 (100) 861 (100) 41.96 < 0.001 Married 2,331 (90.7) 513 (82.9) 2,542 (91.2) 861 (83.8) No spouse 238 (9.3) 106 (17.1) 246 (8.8) 166 (16.2) Smoking, N (%) 2,495 (100) 579 (100) 0.80 0.371 2,723 (100) 973 (100) 2.13 0.144 Current smoking 1,588 (63.6) 357 (61.7) 22 (0.8) 13 (1.3) No smoking 907 (36.4) 222 (38.3) 2,701(99.2) 960 (98.7) Drinking, N (%) 2,498 (100) 582 (100) 11.26 0.010 2,721 (100) 974 (100) 1.58 0.664 No drinking 1,625 (65.0) 343 (58.9) 2,687 (98.8) 965 (99.1) 1–2 times per week 549 (22.0) 155 (26.7) 20 (0.7) 5 (0.5) 3–4 times per week 166 (6.7) 52 (8.9) 1 (0.0) 1 (0.1) ≥ 5 times per week 158 (6.3) 32 (5.5) 13 (0.5) 3 (0.3) Regular exercise, N (%) 2,499 (100) 582 (100) 0.10 0.748 2,721 (100) 966 (100) 1.12 0.290 Yes 304 (12.2) 68 (11.7) 298 (10.9) 94 (9.7) No 2,195 (87.8) 514 (88.3) 2,423 (89.1) 872 (90.3) Hypertension, N (%) 2,572 (100) 620 (100) 1.97 0.160 2,788 (100) 1,027 (100) 17.24 < 0.001 Yes 629 (24.5) 135 (21.8) 655 (23.5) 177 (17.2) No 1,943 (75.5) 485 (78.2) 2,133 (76.5) 850 (82.8) Diabetes, N (%) 2,572 (100) 620 (100) 1.89 0.169 2,788 (100) 1,027 (100) 0.14 0.709 Yes 55 (2.1) 19 (3.1) 57 (2.0) 23 (2.2) No 2,517 (97.9) 601 (96.9) 2,731 (98.0) 1,004 (97.8) Stroke, N (%) 2,492 (100) 578 (100) 0.19 0.661 2,707 (100) 969 (100) 0.18 0.675 Yes 17 (0.7) 3 (0.5) 11 (0.4) 3 (0.3) No 2,475 (99.3) 575 (99.5) 2,696 (99.6) 966 (99.7) Note. *When comparing between continuous variable groups, the statistic value represents the t value; when the categorical variable group is compared, the statistic value represents the chi-square value. Table 1. Baseline characteristics of participants at follow-up or lost by gender
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During a mean of 12.5 years of follow-up, 615 death events (364 for males and 251 for females) were documented among 5,360 participants. In the male subgroup, the lowest density of death was 698/100,000 person-years in the fifth WC group (90.0–94.9 cm). With WC group 5 as the reference group, Cox regression analysis showed that the risk of death increased in groups 1, 2, 3, and 7. The HR value and 95%
FCIs of groups 1, 2, 3, and 7 were 2.13 (1.79–2.52), 1.70 (1.35–2.14), 1.34 (1.05–1.72), and 2.17 (1.20–3.92), respectively. After adjusting for age, BMI, education, occupation, marital status, smoking, drinking, and regular exercise, WC groups 1 [1.60 (1.35–1.90)] and 2 [1.40 (1.11–1.76)] were significantly associated with high risk of all-cause mortality. In the female subgroup, the lowest density of death was 588/100,000 person-years in the sixth WC group (90.0–94.9 cm). With WC group 5 as the reference group, Cox regression analysis showed that the risk of death increased in group 7. The HR value and 95% FCI were 2.01 (1.19–3.39). After multivariable adjustment, groups 1, 2, and 7 were significantly associated with high risk of all-cause mortality. The adjusted HRs of groups 1, 2, and 7 were 1.43 (1.11–1.83), 1.39 (1.05–1.84), and 1.91 (1.13–3.22), respectively (Table 2).
WC groups (cm) Death (n) Persons years Death density
(/100 thousand PY)HR
(95% FCI)Adjusted HR*
(95% FCI)Male 1 < 75.0 134 8,975 1,493 2.13 (1.79−2.52) 1.60 (1.35−1.90) 2 75.0−79.9 76 6,243 1,217 1.70 (1.35−2.14) 1.40 (1.11−1.76) 3 80.0−84.9 62 6,620 937 1.34 (1.05−1.72) 1.15 (0.90−1.48) 4 85.0−89.9 44 4,606 955 1.34 (0.99−1.80) 1.22 (0.90−1.64) 5 90.0−94.9 22 3,152 698 1.00 (0.66−1.52) 1.00 (0.66−1.52) 6 95.0−99.9 15 1,399 1,072 1.54 (0.93−2.55) 0.93 (0.56−1.54) 7 ≥ 100.0 11 730 1,507 2.17 (1.20−3.92) 1.72 (0.95−3.11) Female 1 < 70.0 63 8,068 781 1.22 (0.95−1.57) 1.43 (1.11−1.83) 2 70.0−74.9 49 7,170 683 1.09 (0.82−1.44) 1.39 (1.05−1.84) 3 75.0−79.9 50 7,718 648 1.03 (0.78−1.36) 1.23 (0.94−1.63) 4 80.0−84.9 41 5,979 686 1.09 (0.80−1.48) 1.14 (0.84−1.55) 5 85.0−89.9 23 3,653 630 1.00 (0.66−1.50) 1.00 (0.66−1.50) 6 90.0−94.9 10 1,702 588 0.93 (0.50−1.73) 0.61 (0.33−1.14) 7 ≥ 95.0 15 1,114 1,346 2.01 (1.19−3.39) 1.91 (1.13−3.22) Note. *Adjusted by age, BMI, education, occupation, marital status, smoking, drinking, and regular exercise. Table 2. Death density and multivariate adjusted HR (95% FCI) by gender and WC groups
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The lowest densities of death were 436/100,000 person-years for males younger than 60 years old and 2,498/100,000 person-years for elderly males (age ≥ 60 years old) in the fifth WC group (90.0–94.9 cm). For males younger than 60 years old, Cox regression analysis showed that WC was not significantly associated with high risk of all-cause mortality in each group. Different results were found in elderly males. The risk of death increased in groups 1, 2, and 3 after multivariate adjustment. The adjusted HR values and 95%
FCIs of groups 1, 2, and 3 were 2.03 (1.65–2.49), 1.67 (1.24–2.25), and 1.41 (1.02–1.95), respectively (Table 3). WC groups (cm) Death (n) Persons years Death density
(/100 thousand PY)HR
(95% FCI)Adjusted HR*
(95% FCI)Male < 60 years old (N = 2,088) 1 < 75.0 43 7,284 590 1.32 (0.98−1.79) 1.34 (0.99−1.82) 2 75.0−79.9 31 5,265 589 1.35 (0.95−1.92) 1.30 (0.91−1.84) 3 80.0−84.9 25 5,673 441 1.01 (0.68−1.49) 0.96 (0.65−1.43) 4 85.0−89.9 21 3,973 529 1.15 (0.74−1.79) 1.19 (0.76−1.84) 5 90.0−94.9 12 2,751 436 1.00 (0.57−1.76) 1.00 (0.57−1.76) 6 95.0−99.9 6 1,186 506 1.16 (0.52−2.59) 1.17 (0.52−2.59) 7 ≥ 100.0 4 615 651 1.50 (0.56−4.00) 1.44 (0.54−3.83) ≥ 60 years old (N = 484) 1 < 75.0 91 1,691 5,381 2.22 (1.81−2.73) 2.03 (1.65−2.49) 2 75.0−79.9 45 978 4,600 1.78 (1.32−2.41) 1.67 (1.24−2.25) 3 80.0−84.9 37 947 3,905 1.59 (1.15−2.19) 1.41 (1.02−1.95) 4 85.0−89.9 23 633 3,634 1.46 (0.97−2.20) 1.35 (0.90−2.04) 5 90.0−94.9 10 400 2,498 1.00 (0.54−1.86) 1.00 (0.54−1.86) 6 95.0−99.9 9 213 4,216 1.73 (0.90−3.32) 1.06 (0.55−2.03) 7 ≥ 100.0 7 115 6,068 2.54 (1.21−5.33) 1.98 (0.94−4.15) Female < 60 years old (N = 2,381) 1 < 70.0 20 7,122 281 1.47 (0.95−2.28) 1.73 (1.11−2.67) 2 70.0−74.9 16 6,443 248 1.30 (0.80−2.12) 1.38 (0.85−2.26) 3 75.0−79.9 21 6,759 311 1.62 (1.06−2.49) 1.66 (1.08−2.55) 4 80.0−84.9 14 5,151 272 1.42 (0.84−2.40) 1.49 (0.88−2.52) 5 85.0−89.9 6 3,134 191 1.00 (0.45−2.23) 1.00 (0.45−2.23) 6 90.0−94.9 5 1,424 351 1.84 (0.76−4.41) 1.73 (0.72−4.16) 7 ≥ 95.0 5 947 528 2.77 (1.15−6.64) 2.55 (1.06−6.13) ≥ 60 years old (N = 407) 1 < 70.0 43 945 4,549 1.38 (1.02−1.87) 1.23 (0.91−1.66) 2 70.0−74.9 33 727 4,541 1.43 (1.02−2.01) 1.42 (1.01−2.00) 3 75.0−79.9 29 960 3,022 0.92 (0.64−1.32) 0.91 (0.63−1.30) 4 80.0−84.9 27 828 3,262 1.00 (0.69−1.47) 1.13 (0.78−1.65) 5 85.0−89.9 17 519 3,274 1.00 (0.62−1.61) 1.00 (0.62−1.61) 6 90.0−94.9 5 278 1,800 0.54 (0.22−1.29) 0.35 (0.15−0.85) 7 ≥ 95.0 10 168 5,957 1.70 (0.88−3.27) 2.11 (1.10−4.06) Note. *Adjusted by BMI, education, occupation, marital status, smoking, drinking, and regular exercise. Table 3. Death density and multivariate adjusted HR (95% FCI) by gender, age, and WC groups
The lowest densities of death were 191/100,000 person-years for females younger than 60 years old in the fifth WC group (85.0–89.9 cm) and 1,800/100,000 person-years for elderly females (aged ≥ 60 years old) in the sixth WC group (90–94.9 cm). With WC group 5 as the reference group, after multivariable adjustment, those in groups 1, 3, and 7 had high risks for all-cause mortality among female age < 60 years old. The adjusted HR values and 95%
FCIs of groups 1, 3, and 7 were 1.73 (1.11–2.67), 1.66 (1.08–2.55), and 2.55 (1.06–6.13), respectively. However, for elderly females, WC groups 2 [1.42 (1.01–2.00)] and 7 [2.11 (1.10–4.06)] were significantly associated with high risk of all-cause mortality after multivariable adjustment. In addition, WC group 6 [0.35 (0.15–0.85)] was significantly associated with low risk of all-cause mortality (Table 3). -
Table 4 shows the detailed results of sensitivity analysis by various methods. Excluding current smokers modified the HR estimates materially. Multivariable-adjusted HRs fluctuated; they decreased in groups 1–3 and increased in groups 6 and 7 among men. Adjusted HRs rose slightly in each group among women. By excluding the participants who had self-reported stroke, self-reported hypertension and diabetes, or detected at baseline, adjusted HRs for males decreased in groups 2 and 3 and increased in groups 1, 4, 6, and 7; adjusted HR for female decreased in each group. Excluding participants who died from accidental causes, adjusted HR declined in each group except in group 7 among males; adjusted HRs decreased in groups 1–4 and stabilized in groups 6 and 7 among females. Excluding participants who died during the first 2 years of follow-up, adjusted HRs declined in each group, except in group 6 and 7 among men, and declined in each group, except in group 2 among women.
WC groups
(cm)Excluding current
smokersExcluding subjects with stroke, hypertension or diabetes at baseline Excluding accidental
deathExcluding death within the first 2 years of
follow-upHR
(95% FCI) Adjusted HR*
(95% FCI)HR
(95% FCI)Adjusted HR*
(95% FCI)HR
(95% FCI)Adjusted HR*
(95% FCI)HR
(95% FCI)Adjusted HR*
(95% FCI)Male N = 984 N = 1,903 N = 2,545 N = 2,530 1 < 75.0 1.82
(1.38−2.40)1.52
(1.15−2.00)2.87
(2.34−3.51)1.74
(1.42−2.13)2.12
(1.78−2.52)1.55
(1.30−1.84)2.16
(1.81−2.58)1.46
(1.23−1.75)2 75.0−79.9 1.41
(0.99−2.02)1.27
(0.89−1.82)1.84
(1.37−2.48)1.21
(0.90−1.63)1.64
(1.29−2.08)1.31
(1.03−1.66)1.57
(1.23−2.02)1.21
(0.94−1.55)3 80.0−84.9 1.10
(0.75−1.62)0.95
(0.65−1.39)1.37
(0.96−1.96)1.09
(0.76−1.56)1.21
(0.92−1.58)1.05
(0.80−1.38)1.38
(1.07−1.79)1.14
(0.88−1.47)4 85.0−89.9 1.37
(0.89−2.09)1.23
(0.80−1.89)1.42
(0.93−2.18)1.32
(0.86−2.03)1.34
(0.98−1.82)1.20
(0.88−1.63)1.17
(0.83−1.63)1.03
(0.73−1.44)5 90.0−94.9 1.00
(0.55−1.81)1.00
(0.55−1.81)1.00
(0.52−1.92)1.00
(0.52−1.92)1.00
(0.65−1.53)1.00
(0.65−1.53)1.00
(0.65−1.55)1.00
(0.65−1.55)6 95.0−99.9 1.50
(0.71−3.14)1.15
(0.55−2.42)1.36
(0.51−3.62)1.08
(0.41−2.88)1.50
(0.89−2.54)0.88
(0.52−1.49)1.59
(0.94−2.68)0.98
(0.58−1.66)7 ≥ 100.0 2.82
(1.35−5.92)1.79
(0.86−3.76)1.46
(0.36−5.82)1.93
(0.48−7.72)2.27
(1.26−4.10)1.80
(0.99−3.24)2.40
(1.33−4.34)2.08
(1.15−3.76)Female N = 2,766 N = 2,094 N = 2,779 N = 2,755 1 < 70.0 1.27
(0.99−1.63)1.48
(1.16−1.90)1.23
(0.90−1.67)0.84
(0.62−1.14)1.16
(0.90−1.50)1.35
(1.05−1.75)1.03
(0.78−1.36)1.31
(0.99−1.73)2 70.0−74.9 1.13
(0.85−1.49)1.45
(1.10−1.92)1.07
(0.75−1.53)0.83
(0.58−1.18)1.07
(0.80−1.41)1.38
(1.04−1.83)1.07
(0.80−1.43)1.44
(1.07−1.92)3 75.0−79.9 1.04
(0.79−1.38)1.27
(0.96−1.68)0.75
(0.49−1.14)0.65
(0.42−0.99)1.01
(0.76−1.33)1.22
(0.92−1.61)0.95
(0.70−1.27)1.14
(0.85−1.54)4 80.0−84.9 1.13
(0.83−1.54)1.20
(0.89−1.64)0.49
(0.25−0.93)0.37
(0.19−0.71)1.02
(0.74−1.40)1.08
(0.78−1.48)0.97
(0.70−1.36)1.02
(0.73−1.43)5 85.0−89.9 1.00
(0.66−1.52)1.00
(0.66−1.52)1.00
(0.55−1.81)1.00
(0.55−1.81)1.00
(0.66−1.50)1.00
(0.66−1.50)1.00
(0.66−1.52)1.00
(0.66−1.52)6 90.0−94.9 0.98
(0.53−1.83)0.68
(0.36−1.26)0.96
(0.36−2.56)0.47
(0.18−1.24)0.93
(0.50−1.73)0.61
(0.33−1.13)0.78
(0.39−1.55)0.55
(0.27−1.10)7 ≥ 95.0 2.10
(1.24−3.54)2.03
(1.20−3.43)1.82
(0.82−4.05)1.63
(0.73−3.62)2.01
(1.19−3.39)1.91
(1.13−3.22)1.96
(1.14−3.37)1.80
(1.05−3.10)Note. *Adjusted by age, BMI, education, occupation, marital status, smoking, drinking, and regular exercise. Table 4. Multivariate adjusted HR (95% FCI) in sensitivity analysis