The risk of these benign -- but potentially large and painful -- womb growths seems to rise in tandem with the amount of time spent sitting or lying down during the day, showed the findings published in the open access journal BMJ Open.

Uterine fibroids are the most common benign tumours in women of childbearing age, varying in prevalence from 4.5 per cent to 69 per cent.

These growths may not produce any symptoms, but they may also be associated with abnormal bleeding, pelvic and abdominal pain, and infertility, among other things.

"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," said the researchers from Kunming Medical University in China.

Sedentary behaviour is associated with tumours that rely on the female hormone oestrogen, such as endometrial, ovarian, and breast cancers; uterine fibroids are also fueled by oestrogen.

The researchers therefore wanted to find out if there might be a link between extensive sedentary leisure time and the risk of uterine fibroids.

The study included 6,623 women aged 30 to 55 who had not yet gone through the menopause.

Sedentary behaviour was classified as 1.5 or fewer metabolic equivalent of task (MET) hours/day when sitting or lying down. METs express how much energy in calories is expended per hour of physical activity.

In all, 562 (8.5 per cent) of the women had uterine fibroids, the prevalence of which increased with age. Rates were highest (2.5 times higher) among those aged 50 and older.

While sedentary leisure time wasn't associated with the prevalence of fibroids in premenopausal women, it was associated with the prevalence of fibroids in perimenopausal women: the risk was five times higher among those who clocked up six or more sedentary leisure hours a day than it was in those who clocked up fewer than 2 hours.

This is an observational study, and as such, can't establish causal factors. The study also relied on subjective assessment for many of the factors, point out the researchers.

But one possible explanation for the observed associations might be that sedentary behaviour is related to obesity, which is a risk factor for uterine fibroids, say the researchers. Both sedentary behaviour and obesity increase the body's oestrogen level.

Other possible explanations include the known associations between sedentary behaviour and metabolic disorders, chronic inflammation, and vitamin D deficiency, they said. IANS/KB