Sitting For Over 6 Hours A Day Linked To Increased Risk Of Fibroids

Uterine fibroids are the most common benign tumors among women of childbearing age, according to the researchers they vary in prevalence from 4.5% to 69%. These growths may not produce any symptoms, but they may be associated with abnormal bleeding, pelvic pain, abdominal pain, and infertility among other symptoms. 

Sedentary behaviors are associated with tumors that rely on estrogen, such as ovarian, breast, and endometrial cancers, but uterine fibroids are also fueled by estrogen. The risk of this mostly benign but potentially large and painful womb growth appears to increase in tandem with the amount of time that a woman spends sitting or lying down throughout the day. 

To investigate whether or not there is a link between excessive sedentary time and the risk of developing uterine fibroids, the researchers utilized data from the Yunnan cohort of the community-based long-term China Multi-Ethnic Cohort Study which involves 99,556 participants from 5 provinces. 

This study included data from 6623 women between the ages of 30-55 years old who had not gone through menopause such as basic background information, contraceptive use, menstrual/reproductive history, number of children, age of childbirth, diet, height, weight (BMI), activity level, and sedentary time. 

Participants specified how much time they spent playing games, reading, knitting, as well as viewing screen time or other similar activities; responses were divided into four sedentary leisure time groups: under two hours a day, 2-3.99 hours a day, 4-5.99 hours a day, and 6 or more hours a day. 

The analysis revealed that the average age of their first menstrual cycle was between the ages of 13 to 16 years old, nearly 84% of the women gave birth to more than two children and the average age of their first childbirth was between the ages of 20-24 years old. 61% of the women had 2-3.99 hours of sedentary leisure time per day. 

Overall, 562 of the women developed uterine fibroids with an average prevalence rate of 8.5%, the prevalence increased with age, with the rates being highest among those aged 50 or older at 2.5 times higher. Weight (BMI), the number of births (more than 2), menstrual status, time since last birth (13-17 years or more) activity levels, and sedentary time were all associated with uterine fibroids. 

According to the researchers, the more sedentary time spent the greater the risk for uterine fibroids, and after taking into account a variety of potentially influential factors, sedentary leisure time of six or more hours per day was found to be associated with a risk that was twice of that for women who spent less than two hours a day of sedentary leisure time. 

Sedentary leisure time was not associated with the prevalence of fibroids in premenopausal women, but it was associated with the prevalence of fibroids in perimenopausal women. The analysis revealed the risk was 5 times higher among those who spent six or more hours a day of sedentary time than those who spent less than two hours a day of sedentary leisure time. 

Due to the nature of observational studies, the researchers were not able to establish causal factors. However, the researchers suggest that one possible explanation for the associations may be due to the fact that sedentary behavior is related to obesity, which is a risk factor for uterine fibroids, and both obesity and sedentary behavior increase estrogen levels. Other possibilities may include the known associations between metabolic disorders, chronic inflammation, vitamin D deficiency, and sedentary behaviors. 

The researchers concluded that “This cross-sectional study, based on the natural population, showed that [sedentary leisure time] has a linear positive correlation with [uterine fibroids], indicating that [it] may be an independent risk factor.”