Abstract
To examine the association between body mass index (BMI), use of menopausal hormone therapy (HT), and incidence of uterine fibroids in postmenopausal women, 610,604 postmenopausal women without prior hysterectomy or diagnosis of fibroids were followed as part of a large United Kingdom prospective cohort study. We used Cox regression models to calculate adjusted relative risks (RRs) of surgically-confirmed fibroids (defined as a hospital admission with uterine fibroids as a primary diagnosis with a related surgical procedure), in relation to BMI and use of HT. During an average of 11.4 years of follow-up, 3561 women were admitted to hospital with surgically-confirmed fibroids. Five-year incidence rates decreased with age, from 0.50 % (1 in 200 women) at age 50–54, to 0.11 % (1 in 1000 women) at age 75–79. The 5-year rate in postmenopausal women aged 50–54 was about a quarter that seen in premenopausal women of the same age (1 in 200 vs. 1 in 50). Compared with normal weight women, obese women had a RR of surgically-detected fibroids of 1.46 (95 % CI 1.33–1.59; p < 0.0001). HT use was associated with a RR of 2.33 (95 % CI 2.18–2.49; p < 0.0001) in ever versus never users. When we analysed HT use and BMI together, obese vs. normal weight never users had a RR of 2.00 (95 % CI 1.77–2.26): the highest risks were seen in women who were obese and had ever used HT, RR = 3.30 (95 % CI 2.88–3.79). Uterine fibroids continue to occur in postmenopausal women; obesity and hormone therapy use are important modifiable risk factors.
Highlights
Uterine fibroids are benign monoclonal smooth muscle tumours of the uterus [1], and are the most common pelvic tumour in women [2]
We investigated whether women who had ever used hormone therapy (HT) were at an increased risk of fibroids, and whether the use of HT modified the association with body mass index (BMI)
We have used the term ‘incidence rate’ throughout the study, surgically-confirmed fibroids in postmenopausal women represent a subset of true incidence; cases in our analysis are those in which uterine fibroids, or a co-morbid condition, have resulted in a surgical diagnosis of fibroids
Summary
Uterine fibroids are benign monoclonal smooth muscle tumours of the uterus [1], and are the most common pelvic tumour in women [2]. Factors that increase exposure to oestrogen appear to increase the incidence of uterine fibroids [10]. The Million Women Study provides a unique opportunity to examine the relationship between adiposity, HT use and the incidence of uterine fibroids in postmenopausal women. This prospective cohort study collected detailed information at recruitment on participants’ menopausal status, use of HT, and height and weight. We have used the term ‘incidence rate’ throughout the study, surgically-confirmed fibroids in postmenopausal women represent a subset of true incidence; cases in our analysis are those in which uterine fibroids, or a co-morbid condition, have resulted in a surgical diagnosis of fibroids
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