Patrick Roberts and Kemba Peters | Childbearing and breastfeeding – How breast cancer incidences are reduced among poorer women
We previously highlighted how socio-economic status affects early detection of breast cancer, prompt treatment, and overall survival among ‘lower-class’ women. An important realisation was that women from less affluent regions suffered higher mortality rates, despite the lower incidences of breast cancer. This sequel to our first article will focus on the disparity in incidence among poorer women and factors that have protected them from breast cancer. This includes a younger age of first pregnancy, multiple pregnancies, a longer duration of breastfeeding, lower incidences of obesity, and hormonal medications.
First, it is essential to highlight a well-established, direct link between increasing oestrogen exposure and an increased risk of breast cancer. Oestrogen is a female hormone that plays a vital role in developing female sexual characteristics and regulating the menstrual cycle. However, oestrogen also drives the division of mammary cells in the breast and, therefore, breaks in exposure are favourable. The factors that alter oestrogen exposure throughout a woman’s lifetime include both modifiable and non-modifiable factors.
Non-modifiable factors include:
1. Age of menarche (commencement of the first monthly period);
2. Age of menopause (cessation of monthly periods).
An earlier age of menarche and a later age of menopause suggest more significant exposure to oestrogen and, therefore, an increase in the risk of breast cancer. A woman who attains menarche at 11 years has a five per cent reduced rate of breast cancer, compared to a woman who attained menarche at 10 years old. Similarly, a woman who achieves menopause at 50 years old has a three per cent increased risk of breast cancer than a woman who attains menopause at 49 years old. The menstrual cycle is variable among women and based solely on individual genetic and inherited factors, regardless of socio-economic status.
However, there is considerable variability in the modifiable factors between more affluent and less affluent women. These factors are the products of a woman’s environment and socialisation. The modifiable factors include:
1. Nulliparity (a woman who has never given birth to a child);
2. Age of first pregnancy;
3. Number of pregnancies;
4. Duration of breastfeeding;
5. Use of hormonal treatment/estrogen-based contraception and in vitro fertilisation;
6. Obesity and lifestyle factors.
The influence of pregnancy on breast cancer is twofold, as pregnancy increases oestrogen in the blood. There is a short-lived, increased risk of breast cancer five years after initial pregnancy, most significantly in older women. Hence, advanced maternal age (first child at age 35 or older) has been linked to an increased risk of breast cancer. However, overwhelming data confirm that the long-term effect of pregnancy is protective, especially when compared with individuals who have had no pregnancies. Nullparity also increases the risk of breast cancer. This protection associated with pregnancy grows with an increasing number of children, with a fall in relative risk by seven per cent with each birth. Also, a woman who has her first child at 20 years has a 30 per cent lower risk of breast cancer than a woman who has her first child at 35 years. Breastfeeding also conveys a modest decrease in breast cancer risk, as it suppresses oestrogen through the production of other hormones.
The traditional pattern of childbearing and breastfeeding has evolved, especially among women in developed countries. The average career woman will delay her childbearing and have her first child much later, and fewer children, on average throughout her lifetime. The duration of breastfeeding is also shorter, often due to the need to resume work. Some women may even choose not to have children in pursuit of their careers.
According to the World Bank data, Jamaica’s fertility rate in 2019 was estimated to be 1.96 births per woman, coming from an initial 5.31 births per woman in 1971. The fertility rates of developed countries, such as the United States, Canada, and the United Kingdom, were 1.70, 1.47 and 1.65 births per woman, respectively, in 2019. Jamaica’s fertility rate and that of other developing countries are higher. This is despite a smaller population. Jamaica’s fertility rate remains relatively stable, while that of the United States continues to fall – from 1.70 to 1.67 births per woman in 2020. This highlights two important points: the evolution of traditional childbearing practices with time, and the ongoing differences in childbearing activity between developing and developed countries.
‘Two is better than too many’ was coined to reduce fertility rates in Jamaica. While current figures reflect this initial goal, a single figure does not reflect the actual pattern of births. Dissimilarity in fertility rates is still apparent when looking within Jamaica, between parishes and regions. The traditional pattern of childbearing is still often seen in certain sectors and regions, and has been a feature of less affluent women, whose first pregnancy is often younger and usually proceeds multiple pregnancies. The rate of adolescent pregnancies, which is a feature seen among poorer women, was approximately 50 births per 100,000 adolescent women in 2019.
Obesity has been associated with increased rates of breast cancer, particularly among postmenopausal women. Obesity has commonly been attributed to wealthier women. However, further research is needed to elucidate its occurrence and distribution in our local setting. Oral contraceptives (OCPs) that are oestrogen-based introduce an outside source of oestrogen to the body. But some writers suggest an increased risk. OCPs are commonly used to facilitate family planning and delays in childbearing, another factor commonly seen in career women. The risk is transient and disappears with the discontinuation of OCPs.
Finally, added to the factors discussed above, the uptake of in vitro fertilisation (IVF) among more affluent women in our local setting must be considered. The information regarding IVF and its role in breast cancer has been conflicting. IVF requires particular hormonally based medications that enhance estrogen production to induce the production of eggs. Due to its direct effect on oestrogen, some writers have documented an associated, increased risk of breast cancer, especially in the absence of a subsequent pregnancy.
Socio-economic factors such as the younger age of pregnancy, multiple pregnancies, and longer duration of breastfeeding are among the factors that continue to protect many of our women from breast cancer. This must be combined with education, as the ultimate goal is to improve survival and mortality rates.
- Dr Patrick Roberts is a consultant surgeon at the University Hospital of the West Indies (UHWI), Mona, and Dr Kemba Peters is a resident surgeon at UHWI. Email feedback to firstname.lastname@example.org.