A new study reveals that staying active can erase the breast cancer risk tied to long hours of sitting for obese women, underscoring the power of daily movement for prevention.
Study: Association between daily sitting time and breast cancer among obese women: a nationwide population-based study. Image Credit: Studio Romantic / Shutterstock
Obese and physically inactive women who spend a prolonged period of time in a sitting position are at a significantly higher prevalence of breast cancer, as reported by a study published in the journal BMC Women’s Health. However, this association was not observed in obese women who were physically active.
Background
Obesity is a chronic metabolic condition caused by excessive accumulation of fat in the body, especially in the abdomen. A body mass index (BMI) above 30 kg/m2 is defined as obesity, according to the World Health Organization (WHO).
Globally, more than 600 million people are living with obesity, with women having a higher prevalence than men. Obesity in women is associated with many health complications, including abnormal uterine bleeding, endometriosis, polycystic ovary syndrome (PCOS), infertility, and certain cancers.
Sedentary behavior, defined by any activity with energy expenditure below 1.5 metabolic equivalents, is a modifiable risk factor of many health complications, including cardiovascular and respiratory disorders, insulin resistance, muscle weakness, and reduced energy expenditure. All these conditions can potentially increase the risk of obesity and metabolic syndrome.
Prolonged daily sitting as a sedentary behavior has been found to be associated with increased prevalence of breast cancer in the general female population. However, evidence linking sedentary behavior with breast cancer prevalence in high-risk populations, such as obese women, is lacking.
The current study, led by researchers at the Meizhou People’s Hospital, China, aimed to investigate the association between daily sitting time and breast cancer prevalence in obese women and examine the role of physical activity in mitigating this association.
Study design
The researchers analyzed data derived from the National Health and Nutrition Examination Survey (NHANES), which is an ongoing health and nutrition assessment survey conducted by the National Center for Health Statistics in the United States since 1999.
A total of 9706 obese women from the survey were included in this study. The participants were divided into four groups depending on their daily sitting duration. The sitting durations were less than four hours per day, four to six hours per day, six to eight hours per day, and more than eight hours per day.
The impact of daily sitting time on breast cancer prevalence was assessed after adjusting for socio-demographic, lifestyle, and medical confounding factors. Breast cancer status was self-reported, which may introduce misclassification bias.
Key findings
The analysis of the NHANES database led to the identification of 271 breast cancer cases among the entire study population of 9706 obese women. A significant variation in the breast cancer prevalence was observed among women with different durations of daily sitting.
Specifically, a significantly higher prevalence of breast cancer was observed among women with higher sedentary time (4-6 hours, 6-8 hours, and more than 8 hours) compared to those with lower sedentary time (less than 4 hours). Among physically inactive obese women, the fully adjusted odds ratios (ORs) for breast cancer were 2.56 (95% CI: 1.53–5.86) for 4–6 hours, 2.12 (1.40–4.80) for 6–8 hours, and 2.43 (1.37–5.84) for more than 8 hours, compared to those sitting less than 4 hours per day, demonstrating a nonlinear dose-response relationship. In contrast, no significant increase in breast cancer prevalence was found in physically active obese women at any sitting duration.
The risk was particularly pronounced in certain subgroups: women aged 60 years or above, non-Hispanic whites, women with higher educational background, post-menopausal women, and those with higher obesity levels (BMI ≥35 kg/m²).
Study significance
The study findings reveal that a daily sedentary time of more than four hours is associated with a higher prevalence of breast cancer in obese women, but only in those who are physically inactive. Regular physical activity completely mitigated the association, with active women showing no elevated prevalence regardless of sitting time.
The association between sedentary behavior and breast cancer prevalence is more pronounced among women aged 60 years or above, non-Hispanic whites, women with higher educational background, post-menopausal women, and those with higher obesity levels.
An imbalance in sex hormone levels can potentially increase the risk of breast cancer. Existing evidence indicates that reducing sex hormone levels with regular physical activity can be associated with reduced breast cancer risk, potentially increase anti-cancer immunity, and improve cancer prognosis.
Sedentary behaviors are also known to increase hormone levels due to obesity, insulin resistance, and systemic inflammation, which may collectively contribute to the development of breast cancer.
Another notable finding of the study is the beneficial impact of physical activity in mitigating the adverse association of prolonged sitting time on breast cancer prevalence. Regular physical activity has many physiological benefits, including reduction of visceral adipose tissue, regulation of sex and metabolic hormonal levels, reduction of inflammation, and improvement of insulin sensitivity. These benefits collectively can potentially reduce the risk of breast cancer and improve its prognosis.
Overall, the study findings suggest that physical activity can be considered a promising intervention to help reduce breast cancer prevalence in obese women, especially in older and post-menopausal women. In these high-risk populations, priority should be given to reducing sitting time to less than four hours per day and to engaging in physical activity to counteract metabolic and hormonal imbalances.
Because of the cross-sectional design, the study could not establish direct causal associations between daily sitting time and breast cancer prevalence. Future longitudinal studies are needed to explore whether prolonged sitting precedes breast cancer diagnosis or reflects post-diagnosis behavioral changes. It is also important to note that breast cancer diagnosis in this study was self-reported, which may introduce bias.