For mothers: breastfeed if you can

Evidence

There is probable evidence that:

• Lactation protects the mother against breast cancer.
• Having been breastfed protects children against excess weight gain and overweight and obesity. In turn, this acts to reduce the risk of those cancers for which weight gain and overweight and obesity are a cause.

Exclusive breastfeeding is defined as giving a baby only breastmilk (including breastmilk that has been expressed or is from a wet nurse) and nothing else. The benefits for both mother and baby are greater the longer the duration of breastfeeding. There are special situations where breastfeeding is recommended with caution or not advised, such as for mothers with HIV/AIDS.

Breastfeeding is vital in parts of the world where water supplies are not safe. It is also important for the development of the bond between mother and child. The Recommendation is consistent with a large body of evidence supporting the role of breastfeeding in promoting other aspects of health throughout the lifecourse.

In most countries, however, only a minority of mothers exclusively breastfeed their babies until 4 months, and an even smaller number until 6 months. Increasing the rate of exclusive breastfeeding is one of WHO’s Global Nutrition Targets 2025.

Additional information

In general, the taller people are during adulthood and the more they weighed at birth, the higher their risk of some cancers. There is strong evidence that:

• Developmental factors leading to greater growth in length in childhood (marked by adult attained height) INCREASE the risk of cancers of the pancreas, colorectum, endometrium, ovary, prostate, kidney, skin (malignant melanoma) and breast (pre- and post-menopause)
• Factors that lead to a greater birthweight INCREASE the risk of pre-menopausal breast cancer

Heavier (and longer) babies tend to become taller children and adults. A baby’s birthweight and an adult’s height reflect a complex interplay of genetic, nutritional, and other environmental factors that affect growth within the womb and during childhood and adolescence. Birthweight and height are markers of these factors and therefore are unlikely to affect the risk of cancer directly.

Although adult attained height and birthweight are public health issues, individuals cannot control their own birthweight and it is difficult to influence height after a certain age – which is often before the age that we are able to control our own diets and other environmental factors.  Therefore, the Panel did not make a recommendation on height or birthweight.

Mechanisms

The principal mechanism through which lactation or breastfeeding influence breast cancer risk is through the hormonal influence of the associated period of amenorrhea (absence of a menstrual period) and infertility. This decreases lifetime exposure to menstrual cycles and therefore alters cumulative exposures to specific hormones, particularly androgens, which can influence cancer risk. In addition, the sustained exfoliation of breast tissue during lactation and the epithelial apoptosis at the end of lactation could decrease breast cancer risk through the elimination of cells with DNA damage and mutations.

The mechanisms underlying a lower risk of ovarian cancer among women who have breastfed are not well understood. One hypothesis is that longer periods of amenorrhea (and therefore longer suppression of ovulation) decrease gonadotropin levels and thus lower lifetime exposure to plasma oestradiol.

The mechanisms underpinning cancer risk and adult attained height are thought to be common across many cancers. Specific tissues in taller people are exposed to higher levels of insulin, pituitary-derived growth hormone, and insulin-like growth factors (IGFs), resulting in more cell divisions. This contributes to greater potential for error during DNA replication, resulting in an increased risk of developing cancer.

In addition to these general mechanisms specific mechanisms may influence risk for specific cancers, e.g. taller people have longer intestines and therefore there is greater potential for DNA damage from exposure to mutagenic or cancer-promoting agents leading to colorectal cancer. Taller people have more skin cells, and thus there is greater opportunity for mutations leading to skin cancer development.

Birthweight is a marker of certain aspects of the general fetal growth environment that may influence the development of cancer in later life. Proposed mechanisms include larger infants having a greater number of susceptible cells and in utero programming of IGFs, such as IGF-1, which may lead to greater postnatal cellular proliferation.

Implications for other diseases

Breastfeeding provides short- and long-term benefits for both mother and baby. The incidence of infections, as well as mortality rates, during infancy are lower in children who are breastfed. Benefits continue into childhood and adulthood, with lower risks of other diseases, such as asthma.

Having been breastfed protects against obesity in childhood, and possibly reduces the risk of type 2 diabetes in adulthood. Mothers who breastfeed also have a lower risk of type 2 diabetes.

Public health / policy implications

A whole-of-government, whole-of-society approach is necessary to create environments for mothers that are conducive to breastfeeding their babies and to following our Cancer Prevention Recommendations.

A comprehensive package of policies is needed to promote, protect, and support breastfeeding, including making all hospitals supportive of breastfeeding, providing counselling in healthcare settings, implementing maternity protection in the workplace, and regulating marketing of breastmilk substitutes. Policymakers are encouraged to frame specific goals and actions according to their national context.