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Leading a sedentary life may also affect uterine health. Image Source/Getty Images
  • Fibroids are benign (non-cancerous) tumors in the uterus that can be symptom-free or can cause pain and heavy menstrual bleeding.
  • They affect between 5% and 70% of women, depending on the population studied, and are most common in women in their 40s and 50s.
  • Between 5% and 10% of women in the general population self-report having fibroids and heavy bleeding.
  • Now, a cross-sectional Chinese study suggests that the more time someone spends sitting or lying down during the day, the greater their risk of fibroids during perimenopause.

Uterine fibroids (also known as leiomyoma or ‘myoma’) are muscular tumors that grow in the uterus. It is hard to work out exactly how many women have fibroids because 75% do not cause symptoms severe enough to require treatment, so self-reports will underestimate the prevalence.

On the other hand surveys in gynaecological clinics will overestimate how many women are affected with reports of up to 70% of women. One international online survey of women with heavy bleeding suggested rates of 5-10%. Uterine fibroids are almost always benign (non-cancerous).

Fibroids can range in size from very small to about the size of a grapefruit. Often they have no symptoms, but they can cause pain, heavy menstrual bleeding, and pressure on the bladder and rectum, particularly if large.

Anyone with a uterus can develop fibroids, and the likelihood of developing them increases with age. Other factors that increase the risk of developing fibroids include:

  • being African-American
  • a family history of fibroids
  • obesity
  • hypertension (high blood pressure)
  • never having been pregnant
  • vitamin D deficiency
  • consumption of food additives
  • use of soya milk

Now, a study, published in the BMJ Open, has suggested that a sedentary lifestyle may also increase the risk of developing fibroids, particularly in the years leading up to menopause.

However, this cross-sectional, observational study cannot show a causal link but only an association.

In this study, the researchers collected data from 6,623 female participants from Yunnan Province, southwest China.

The researchers questioned the participants, mostly farmers, about how they spent their leisure time and then physically examined them, including giving them abdominal B-ultrasound examinations to identify whether they had uterine fibroids. They found that 562 (8.5%) had uterine fibroids.

All participants were aged between 30 and 55, were non-menopausal, and did not have any severe mental illnesses.

The researchers carried out face-to-face interviews with digital questionnaires.

These asked participants how much of their leisure time was spent in sedentary activities, such as chess, mobile phones, tablets, TV, books, newspapers, knitting, and other activities where energy consumption was less than or equal to 1.5 metabolic equivalent task (MET).

They divided the cohort into four groups based on how much time they spent in sedentary leisure activities: less than 2 hours per day, 2–3.99 hours per day, 4–5.99 hours per day, and 6 hours or more per day.

In their analysis, the researchers controlled for covariates including age, marital status, education level, body mass index (BMI), age at first period, number of live births, and menstrual status.

The researchers found that more hours of sedentary leisure time were correlated with a greater likelihood of fibroids.

Those who reported six or more hours of sedentary leisure time were twice as likely to have fibroids than those reporting less than two hours. This difference was greatest in those who were perimenopausal, with those in the most sedentary group being more than five times as likely to have fibroids than those with the least sedentary time.

“Study is interesting but it can’t make causal predictions — just associations/correlations. It might be that fibroid growth and/or an unidentified other factor in fibroids, puts people off exercise, leading them to take up sedentary activities, for example?”
— Dr. Sally King, founder of Menstrual Matters, a non-profit online information hub.

Research has linked sedentary leisure behavior with estrogen-dependent cancers, such as breast, ovarian, and endometrial cancer.

Sedentary behavior is also linked to obesity and higher estrogen levels, both of which increase the risk of uterine fibroids, as Dr. G. Thomas Ruiz, board certified OB/GYN at MemorialCare Orange Coast Medical Center in Fountain Valley, California, explained:

“Uterine fibroids are thought to be estrogen-dependent tumors. In the presence of high estrogen, it is believed you’ll get more proliferation of the smooth muscle, fibers, and connective tissue that are responsible for the development of fibroids.”

“Adipose tissue, in general, will convert steroids to estrogen, which is one reason obesity is thought to be linked to a higher probability of breast cancer, endometrial cancer, as well as uterine fibroids,” he added.

In this study, however, sedentary behavior was linked to fibroids only in women with a BMI of less than 24 (healthy weight). The researchers suggest that in overweight or obese individuals, other factors may influence the development of fibroids, lessening the impact of sedentary behavior.

The researchers note several limitations of their study. First, as a cross-sectional study, it cannot determine a causal relationship between sedentary behavior and fibroids.

Dr. Ruiz explained why the researchers might have found the correlation:

“A sedentary lifestyle burns less calories leading to increase levels of fat within the body. This might be the type of study that needs to be repeated in a more diverse population to see if the data holds up.”

But Dr. King cautioned: “Until causality is better proven, the focus on sedentary lifestyle (with extrapolation to assumed obesity) feels a bit more than a neutral observation.”

In the study, the participants also self-reported leisure time and covariates, so there may be memory bias, and although they adjusted for may potential confounding factors, there may be others that they did not adjust for.

Finally, the women of the Yunnan Province are mostly farmers, so the data may not be generalizable to other populations.

Dr. Ruiz pointed out the homogeneity of the study population.

“It’s difficult to assess whether this study is clinically important, as opposed to just an interesting correlation. As China is a homogenous population, how much does [this] data apply to other cultures?” he asked.

Whether a more sedentary lifestyle increases the risk of fibroids or not, there is ample evidence that it can lead to several other health conditions. Hence, experts recommend including more physical activity in leisure time.