A recent study by the Indian Council of Medical Research (ICMR) has highlighted that non-vegetarian diets, poor sleep, and obesity are linked to an increased risk of breast cancer, which is projected to rise by about 5.6 per cent annually, translating into an estimated 0.05 million new cases per year.

“Reproductive timing, hormonal exposure and family history also influence breast cancer risk primarily among Indian women,” stated the study, conducted by ICMR's National Centre for Disease Informatics and Research, Bengaluru.

Globally, breast cancer remains a significant health concern. In 2022, an estimated 2.3 million women were newly diagnosed with the disease, resulting in approximately 670,000 deaths. In India, breast cancer is one of the leading cancer sites, with an estimated 2,21,757 cases reported in 2022, accounting for nearly a quarter (22.8 per cent) of cancers among women.

The ICMR 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 estimated pooled associations between key risk factors and breast cancer.

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

The study found that “early menopause — before 50 years — showed an inverse association with breast cancer, whereas menopause after 50 years was associated with more than a twofold increase in risk.”

Researchers also examined 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. “The risk of breast cancer increased progressively with age at marriage,” the study noted.

It also reported that “women reporting more than two induced abortions had 1.68 times higher risk compared to those with no abortions,” while “late age at first childbirth (more than 30 years) showed markedly elevated risks.”

Most studies found that “breastfeeding duration was not significantly associated with breast cancer risk,” and “oral contraceptive use did not show a significant association.”

Anthropometric findings suggested that “abdominal obesity, measured by waist-to-hip ratio (more than or equal to 0.85), was more strongly associated with breast cancer risk than BMI,” indicating that fat distribution rather than total body mass may be more relevant for Indian women.

Lifestyle factors were also significant contributors. “A non-vegetarian diet was associated with increased risk, consistent with growing evidence on dietary fat intake and may be due to a higher intake of saturated fat and processed meats, which have been linked to estrogen production,” the study said.

Similarly, “poor sleep quality was also associated with increased risk. As evidence of circadian rhythm disruption in cancer development grows, these findings align with this growing body of evidence.” Individual studies further indicated that “irregular sleep patterns and sleeping in a lighted room support the possible role of melatonin suppression in breast cancer development.”

The study added that “elevated stress levels were also reported as significant in individual analyses, although variations in measurement tools and the predominance of cross-sectional designs limit causal interpretation.”

On the other hand, alcohol and tobacco use were “not significantly associated with breast cancer risk, possibly reflecting low prevalence, underreporting, or population-specific biological differences.” The Collaborative Group on Hormonal Factors in Breast Cancer found in a large meta-analysis that “alcohol consumption increases breast cancer risk by 7.1% for every 10 g consumed.”

However, “its contribution to breast cancer incidence in developing countries with low alcohol consumption (0.4 g/day) was negligible, and smoking had little to no independent effect.”