High-Risk Conditions

Lifestyle Risk Factors

Modifiable risk factors are lifestyle-related and may be influenced by personal choices. Understanding and adjusting these risk factors where possible may help lower the risk of developing breast cancer.

Body Weight
Being overweight or obese, especially after menopause, increases breast cancer risk. Excess body fat raises estrogen and insulin levels, which can support tumour growth. Weight gain in adulthood is linked to a higher risk of hormone receptor-positive breast cancer and worse outcomes.

Physical Activity
Regular physical activity helps lower breast cancer risk by regulating hormone levels, reducing inflammation, and supporting a healthy weight. Benefits are seen in both pre- and postmenopausal individuals, even if exercise begins later in life. Aim for at least 150 minutes of moderate to vigorous activity per week to potentially reduce your risk of developing breast cancer by 25–30%.

Alcohol Use
Drinking alcohol, even in small amounts, is consistently linked to increased breast cancer risk. Risk rises with the amount consumed.

Related reading from Our Voices Blog:

• Lifestyle and Nutrition Considerations for Breast Cancer Patients Series, Part 3: Links Between Alcohol and Breast Cancer Recurrence: Can Beer and Wine Increase your Risk?

Diet
No specific food prevents or causes breast cancer, but overall diet quality matters. Diets high in ultra-processed foods, saturated fats, and processed meats are linked to higher risk, while vegetables, fruits, and legumes may be protective. In fact, research suggests that a 10% increase in ultra-processed food intake is associated with an 11% higher risk of developing breast cancer.

Hormone Replacement Therapy (HRT)
Using combined HRT (estrogen + progestin) after menopause increases breast cancer risk, especially with long-term use (5+ years), but the risk declines after stopping. Estrogen-only HRT carries a lower risk and is typically used after hysterectomy. HRT decisions should balance symptom relief with potential risks, including breast cancer.

Smoking
Tobacco smoke contains carcinogens that can damage breast tissue, raising the risk of breast cancer. This risk is particularly high with long-term smoking, exposure to second-hand smoke, or if smoking begins before a first full-term pregnancy. Quitting smoking can lower the risk, even after years of use.

Chemical Exposure
Some environmental chemicals may disrupt hormones or damage DNA, potentially increasing breast cancer risk—especially with long-term or early-life exposure. Chemicals of concern include:

• Pesticides, solvents, and flame retardants
• Ingredients in cosmetics, hair products, and plastics (e.g., parabens, BPA)
• Substances in permanent hair dyes, lawn treatments, and air pollution

Light Exposure at Night (Night Shift Work)
Night shift work and exposure to artificial light during sleeping hours may raise breast cancer risk by interfering with your body’s natural sleep-wake rhythm (circadian rhythm) and lowering melatonin levels. Research is ongoing, but altered sleep-wake cycles and hormone imbalances are possible contributors.

Understanding risk factors is the first step toward informed health decisions. Many individuals with one or more risk factors do not develop breast cancer, and taking steps toward a healthy lifestyle and regular screening can help reduce risk.

Medical Review by Roochi Arora, MD, FRCPC, August 2025

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