Uterine leiomyoma prevalence among young Chinese women
The prevalence of UL in pre-menopausal Chinese women aged between 20 and 50 was 1.6% (2751/171968). This is lower than reported elsewhere,[9, 8] which may be due to the comparatively young age of participants (mean age: 29). BMI was higher among participants with UL (22.56 ± 4.12 kg/m2 vs 23.65 ± 4.35 kg/m2; p < 0.001). The known risk factors for UL of alcohol consumption, first-hand and second-hand tobacco smoke exposure were each confirmed to be positively associated with UL prevalence (p < 0.001). Young women with longer in education (≥ 16 years), non-manual occupation and living in urban areas showed greater prevalence of UL. Younger age at menarche, use of the oral contraceptive pill and higher parity were also associated with greater UL prevalence. Women with hypertension or type 2 diabetes also had significantly higher prevalence of UL (Table 1).
Prevalence of UL by BMI
To understand the association between BMI and UL prevalence, we calculated the odd ratios [9] for UL by BMI category, i.e. underweight, healthy weight, overweight and obese. The analyses were adjusted for age at enrolment, smoking status, passive smoking status, drinking status, education, occupation, region, age at menarche, parity, oral contraceptive use, type 2 diabetes, and hypertension. In young Chinese women, UL prevalence was higher in participants who were overweight (OR 1.30, 95% CI, 1.18–1.42) or obese (OR 1.31, 95% CI, 1.15–1.50) compared to those who are healthy weight (reference) (Table 2). The association with BMI (numerical) and UL prevalence is in eTable 1 in the Supplement.
Table 2
Odds ratios [9] with 95% confidence intervals (95% CIs) for uterine leiomyoma by BMI and stress.
Variable
|
Uterine leiomyoma
|
Crude OR
|
Adjusted OR*
|
P for trend
|
|
No
|
Yes
|
|
|
|
BMI
|
|
|
|
|
|
Underweight
|
13712
|
112
|
0.62 (0.51, 0.74)
|
0.71 (0.59, 0.87)
|
0.049
|
Healthy weight
|
113741
|
1541
|
1.00 (ref)
|
1.00 (ref)
|
Overweight
|
32320
|
791
|
1.81 (1.66, 1.97)
|
1.30 (1.18, 1.42)
|
Obesity
|
12195
|
307
|
1.84 (1.63, 2.08)
|
1.31 (1.15, 1.50)
|
Stress
|
|
|
|
|
|
Yes
|
36885
|
1209
|
2.87 (2.66, 3.09)
|
1.47 (1.34, 1.62)
|
-
|
No
|
135083
|
1542
|
1.00 (ref)
|
1.00 (ref)
|
|
*Adjusted for age at enrolment, smoking status, passive smoking status, drinking status, education, occupation, region, age at menarche, parity, oral contraceptive use, diabetes, and hypertension. |
Psychosocial stress and UL prevalence
To analyse the association between psychosocial stress and development of UL, we calculated adjusted ORs for UL by form and intensity of stress. Within the Young ELEFANT cohort, 20.63% of young Chinese women self-reported that they were under work-related stress (8.73% low stress, 10.24% intermediate, and 1.66% high), 7.70% that they were enduring social stress (6.40% low, 1.22% intermediate, and 0.07% high) and 14.85% reported financial stress (7.62% low, 6.30% intermediate, and 0.93% high) (Table 3). The overlap between forms of self-reported psychosocial stress are shown in eFigure 1 in Additional file 1. Participants reporting multiple forms of stress showed significantly higher prevalence of UL (Table 2). Stratification of stress levels by intensity (none, low, intermediate and high) revealed a gradual increase in UL prevalence with higher levels of stress. UL prevalence was also increased by self-reported social stress (OR 1.33, 95% CI, 1.18–1.51), with a stronger effect observed with intermediate or high levels (OR 1.48, 95% CI, 1.18–1.84). With work-related stress, the ORs for UL were 1.38 (95% CI, 1.22–1.57), 1.48 (95% CI, 1.32–1.66) and 1.72 (95% CI, 1.41–2.10) with low, intermediate and high stress levels, respectively. The ORs of UL associated with financial stress increased steadily with higher levels of stress, ranging from 1.29 (95% CI, 1.14–1.46) with low levels to 1.44 (95% CI, 1.11–1.88) with high levels (Table 3). An association between stress and UL stratified by work type (manual vs non-manual) is shown in eTable 2 in Additional file 1. The analyses were adjusted for age at enrolment, smoking status, passive smoking status, drinking status, BMI, education, occupation, region, age at menarche, parity, oral contraceptive use, type 2 diabetes, and hypertension. Associations between stress and UL by age are displayed in eTable 3 in Additional file 1.
Table 3
Odds ratios [9] with 95% confidence intervals (95% CIs) for uterine leiomyoma by form and intensity of stress.
Variable
|
Uterine leiomyoma
|
Crude OR
|
Adjusted OR*
|
P for trend
|
|
No
|
Yes
|
|
|
Social stress
|
|
|
|
|
|
None
|
159235
|
2301
|
1.00 (ref)
|
1.00 (ref)
|
< 0.001
|
Low
|
10645
|
353
|
2.28 (2.04, 2.55)
|
1.33 (1.18,1.51)
|
Intermediate
|
1969
|
91
|
3.21 (2.61, 3.94)
|
1.48 (1.18, 1.84)
|
High
|
119
|
6
|
Work-related stress
|
|
|
|
|
|
None
|
137701
|
1609
|
1.00 (ref)
|
1.00 (ref)
|
< 0.001
|
Low
|
14668
|
391
|
2.28 (2.04, 2.55)
|
1.38 (1.22, 1.57)
|
Intermediate
|
16908
|
618
|
3.13 (2.85, 3.44)
|
1.48 (1.32, 1.66)
|
High
|
2691
|
133
|
4.18 (3.49, 5.01)
|
1.72 (1.41, 2.10)
|
Financial stress
|
|
|
|
|
|
None
|
147270
|
1942
|
1.00 (ref)
|
1.00 (ref)
|
< 0.001
|
Low
|
12772
|
368
|
2.18 (1.95, 2.44)
|
1.29 (1.14, 1.46)
|
Intermediate
|
10398
|
375
|
2.70 (2.41, 3.02)
|
1.34 (1.18, 1.51)
|
High
|
1528
|
66
|
3.34 (2.61, 4.27)
|
1.44 (1.11, 1.88)
|
*Adjusted for age at enrolment, smoking status, passive smoking status, drinking status, BMI, education, occupation, region, age at menarche, parity, oral contraceptive use, type 2 diabetes, and hypertension. |
High prevalence of uterine leiomyomas in BMI under 24 kg/m2 with psychological stress
We observed that BMI and psychological stress were each associated with UL in the previous analysis. To examine the prevalence of UL in under/healthy weight and overweight/obese individuals self-reporting stress, we dichotomised study participants using a BMI threshold of 24 kg/m2; this is the threshold used to identify overweight/obese individuals according to Chinese guidelines.[25] The prevalence of UL in participants reporting social stress was OR 1.43 (95% CI, 1.25–1.65) among those with a BMI < 24 and 1.23 (95% CI, 1.02–1.49) for those with BMI > 24 (Table 4). The ORs for UL with work-related stress were 1.60 (95% CI, 1.41–1.81) in under/normal weight participants, and 1.25 (95% CI, 1.08–1.46) for overweight/obese participants. Financial stress was associated with increased UL prevalence in both weight groupings, with an OR of 1.41 (95% CI, 1.24–1.59) for under/normal weight individuals and 1.18 (95% CI, 1.01–1.38) for overweight/obese participants. Thus, we observed that the association of UL with any form of stress was stronger in underweight/normal weight individuals in comparison to overweight and obese ones.
Table 4
Odds ratios [9] with 95% confidence intervals (95% CIs) for uterine leiomyoma by psychological stress and BMI.
|
BMI < 24
|
BMI ≥ 24
|
|
Uterine leiomyoma
|
Adjusted OR*
|
Uterine leiomyoma
|
Adjusted OR*
|
|
No
|
Yes
|
|
No
|
Yes
|
|
Social stress
|
|
|
|
|
|
|
No
|
117947
|
1362
|
1.00 (ref)
|
41288
|
939
|
1.00 (ref)
|
Yes
|
9506
|
291
|
1.43 (1.25, 1.65)
|
3227
|
159
|
1.23 (1.02,1.49)
|
Work-related stress
|
|
|
|
|
|
|
No
|
102292
|
929
|
1.00 (ref)
|
35409
|
680
|
1.00 (ref)
|
Yes
|
25161
|
724
|
1.60 (1.41,1.81)
|
9106
|
418
|
1.25 (1.08, 1.46)
|
Financial stress
|
|
|
|
|
|
|
No
|
109462
|
1147
|
1.00 (ref)
|
37808
|
795
|
1.00 (ref)
|
Yes
|
17991
|
506
|
1.41 (1.24, 1.59)
|
6707
|
303
|
1.18 (1.01, 1.38)
|
*Adjusted for age at enrolment, smoking status, passive smoking status, drinking status, education, occupation, region, menarche age, parity, oral contraceptive use, diabetes, and hypertension. |
Interaction between BMI and psychological stress on uterine leiomyoma prevalence
We examined interactions between BMI and psychological stress upon the prevalence of UL (Table 5). In this study, we observed that interaction between stress and underweight (OR 1.16, 95% CI, 1.00-1.34), overweight (OR 0.92, 95% CI, 0.85-1.00) and obesity (OR 0.90, 95% CI, 0.81-1.00) was significant in increasing the ORs for UL.
Table 5
Interaction between BMI and stress for uterine leiomyoma risk.
BMI classification
|
Stress
|
Uterine leiomyoma
|
|
|
Crude OR (95% CI)
|
Adjusted* OR (95% CI)
|
Underweight
|
no
|
0.48 (0.42, 0.55)
|
0.71 (0.61, 0.82)
|
yes
|
1.15 (1.00, 1.34)
|
1.16 (1.00, 1.34)
|
Healthy weight
|
no
|
1.00 (ref)
|
1.00 (ref)
|
yes
|
1.71 (1.61, 1.81)
|
1.26 (1.18, 1.34)
|
Overweight
|
no
|
1.53 (1.42, 1.66)
|
1.20 (1.11, 1.30)
|
yes
|
0.90 (0.84, 0.98)
|
0.92 (0.85, 1.00)
|
Obesity
|
no
|
1.54 (1.40, 1.71)
|
1.22 (1.10, 1.36)
|
yes
|
0.92 (0.83, 1.01)
|
0.90 (0.81, 1.00)
|
*Adjusted for age at enrolment, passive smoking status, drinking status, education, region, age at menarche, and hypertension. Result of likelihood test for interaction variable BMI*stress is significant (P = 0.0029, df = 3). |