Lifestyle and breast cancer risk

Modifying lifestyle choices can help prevent breast cancer.

INTRODUCTION

BREAST cancer remains the most common cancer among Australian women, accounting for 27% of all cancers diagnosed in 20071 and is the second most common cause of cancer-related death.2 

Due to the increasing incidence, significant morbidity and mortality, breast cancer risk-reduction strategies remain a national health priority.3,4

WEIGHT GAIN AND OBESITY

The strongest current evidence for the primary prevention of cancer and for improving outcomes after diagnosis of cancer relate to achieving and maintaining a healthy weight. 

Pre-diagnosis:

There is consistent high-quality evidence that being overweight or obese is an independent risk factor for breast cancer, with data suggesting that women with a BMI of ≥ 28 kg/m2 have a 26% greater relative risk of cancer compared to lean women.5, 6

Obesity is also an independent prognostic factor for development of distant metastases, with 46% increased relative risk after 10 years in those with a BMI ≥ 30 kg/m2 at diagnosis.

Central adiposity and obesity at diagnosis are important modifiable risk factors for breast cancer recurrence, all-cause mortality and comorbid conditions.7,8

Post-diagnosis: 

Weight gain following diagnosis of breast cancer is common, with 50–96% of early-stage breast cancer patients experiencing weight gain (ranging from 1.7–5.0 kg).9 

Risk factors for weight gain appear to be adjuvant chemotherapy, tamoxifen use, decreased physical activity, younger age and premenopausal status at diagnosis.10 

In addition, the fatigue and psychological distress that frequently accompany treatment may impact on lifestyle-related behaviours.2

Importantly, the beneficial effects of chemotherapy and adjuvant hormone therapy seem to be lost more rapidly in obese patents with breast cancer.11 

Weight gain is linked to endocrine and metabolic disturbances that may contribute to the poorer prognosis of women with breast cancer.

Hyperinsulinaemia and insulin resistance that underpin type 2 diabetes have been associated with poorer breast cancer outcome in observational studies.12 Maintenance of a healthy weight throughout the lifespan and the prevention of further weight gain post diagnosis of breast cancer is therefore a priority.6

 ALCOHOL

Consumption of alcohol, even at moderate levels and regardless of beverage type, has been shown to increase breast cancer risk at all ages.13 The effects of alcohol may be mediated by pro-carcinogenic pathways, and nutrient deficiencies including folate.14,3

 NUTRITION

The role of diet in breast cancer prevention and outcomes appears conflicting, with further research required. 

To date, there is no robust evidence suggesting individual foods such as soy products, caffeine, red meat, dairy products and dietary fat increases the risk of breast cancer.3, 4 

Limited evidence suggests a potential protective effect with increased fruit, vegetable and wholegrain consumption.14-16 

The use of antioxidant supplements such as vitamin C, beta-carotenoids and vitamin E also have minimal protective benefits.4,17,18

Cancer is an area in which a multitude of dietary approaches, nutrients and complementary therapies are currently being studied; however, current evidence does not support the specific inclusion of any particular food, nutrient or supplement. 

Nutrition recommendations should therefore promote a healthy well-balanced diet.4

VITAMIN D SUPPLEMENTATION

Inverse relationships have been reported between serum vitamin D levels and breast cancer development, recurrence and mortality.19 

Epidemiological studies in women with breast cancer show approximately 75% of women with newly diagnosed breast cancer are vitamin D deficient.20 

Adequate vitamin D, essential for bone health, is also important, as many women with breast cancer are at risk of osteoporosis either due to early menopause or bone loss associated with aromatase inhibitors.21 

EXERCISE

Consistent evidence indicates moderate physical activity, at around 200 minutes per week, reduces the risk of breast cancer diagnosis and recurrence.22,23 

Exercise is an effective intervention to improve quality of life, cardiorespiratory fitness, physical functioning and fatigue in breast cancer patients and survivors.24

Moreover, there is consistent findings showing a protective effect of regular physical activity and all-cause mortality among breast cancer survivors.25

Key points: Lifestyle and breast cancer

- Take advantage of opportunities to provide evidence-based guidance to women throughout the life cycle regarding the impact of a healthy lifestyle on cancer prevention. 

- Reinforce the importance of maintaining a healthy weight (BMI 20–25 kg/m2) throughout life.

- Maintain a well-balanced diet rich in fruit and vegetables, wholegrains and low-fat diary products. 

- Assist women to make informed decisions regarding moderate alcohol intake.

- Inform women that no specific foods, restrictive diets, supplements or complementary therapies have been identified as being associated with reducing breast cancer risk.

- Monitor vitamin D levels and supplement as per individual needs.

- Encourage women to adopt regular physical activity. 

Samantha Kozica APD BNutrDiet (Hons)

Dietitian and PhD student, Jean Hailes Research,School of Public Health & Preventive Medicine, Monash University

Co-author: Dr Cate Lombard PhD, APD Healthy Lifestyle Program Director. A Helen MacPherson Smith Fellow