Non-vegetarian diet, poor sleep, obesity associated with increased risk of breast cancer: ICMR study

Non-vegetarian diets, poor sleep quality and obesity have been associated with an increased risk of breast cancer, which is expected to rise by about 5.6 per cent annually, leading to an estimated increase of 0.05 million new cases every year, according to a study by the Indian Council of Medical Research (ICMR).

Reproductive timing, hormonal exposure and family history also significantly influence breast cancer risk among Indian women, the study stated. The research was conducted by ICMR’s National Centre for Disease Informatics and Research, Bengaluru.

Globally, an estimated 2.3 million women were newly diagnosed with breast cancer in 2022, resulting in approximately 670,000 deaths. In India, breast cancer remains one of the leading cancer sites, with an estimated 221,757 cases reported in 2022, accounting for nearly 22.8 per cent of all cancers among women.

The study was a systematic review of Indian research assessing breast cancer risk factors among Indian women, covering studies published up to December 22, 2024. A meta-analysis using a random-effects model was conducted to estimate pooled associations between key risk factors and breast cancer.

Of the 1,871 articles identified, 31 studies met the inclusion criteria, with the case-control studies assessed as being of moderate to high quality.

The findings showed that early menopause, before 50 years of age, had an inverse association with breast cancer, while menopause after 50 years was linked to more than a twofold increase in risk.

Reproductive and hormonal factors such as age at marriage, pregnancy, abortion history, age at first and last childbirth, breastfeeding, oral contraceptive use, parity and number of children were also examined. The risk of breast cancer increased progressively with age at marriage. Women reporting more than two induced abortions had a 1.68 times higher risk compared to those with no abortions. Late age at first childbirth, beyond 30 years, was associated with markedly higher risk.

Breastfeeding duration was not significantly associated with breast cancer risk in most studies, and oral contraceptive use also did not show a significant association.

Anthropometric findings indicated that abdominal obesity, measured by a waist-to-hip ratio of more than or equal to 0.85, was more strongly associated with breast cancer risk than body mass index (BMI). This suggests that fat distribution, rather than overall body mass, may be more relevant for Indian women.

Lifestyle factors contributed substantially to variations in breast cancer risk. A non-vegetarian diet was linked to increased risk, consistent with growing evidence on dietary fat intake. This may be due to higher consumption of saturated fats and processed meats, which have been associated with increased estrogen production.

Poor sleep quality was also found to be associated with higher risk. As evidence grows regarding the role of circadian rhythm disruption in cancer development, these findings align with emerging research. Individual studies also indicated that irregular sleep patterns and sleeping in a lighted room may support the role of melatonin suppression in breast cancer development.

Elevated stress levels were reported as significant in some individual analyses, although variations in measurement tools and the predominance of cross-sectional study designs limit causal interpretation.

Conversely, alcohol and tobacco use were not found to be significantly associated with breast cancer risk in this population, possibly due to low prevalence, underreporting or population-specific biological factors. However, the Collaborative Group on Hormonal Factors in Breast Cancer reported in a large meta-analysis that alcohol consumption increases breast cancer risk by 7.1 per cent for every 10 grams consumed.

Despite this, the contribution of alcohol to breast cancer incidence in developing countries with low average consumption, estimated at 0.4 grams per day, was considered negligible, while smoking showed little to no independent effect.