Menarche marks the beginning of the first menstrual cycle. This is a significant event of puberty and helps the body prepare for reproduction. According to the National Health Statistics Report, the mean age of menarche in the United States between 2013 and 2017 was 12.5. Globally, the mean age of menarche is about 13.
The Relationship Between Menstrual Cycles And Breast Cancer Risk
Menarche marks the beginning of the production of female reproductive hormones. These hormones circulate in the body until menopause. During the reproductive years of a woman (the period between menarche and menopause), the levels of the two steroid hormones, estrogen and progesterone, keep fluctuating.
The progesterone levels increase during the luteal phase. It is the highest during the mid-luteal phase and decreases when periods start. Progesterone is responsible for thickening the endometrium walls and preparing the body for a possible pregnancy. The estrogen levels increase twice during each menstrual cycle - once during the mid-follicular phase and once during the mid-luteal phase.
The follicular phase is the phase between the first day of menstruation and the next ovulation day. It lasts between 14 and 16 days. The luteal phase is the phase after ovulation until the next menstrual cycle. This lasts for 11-17 days.
The lifetime cumulative number of menstrual cycles is a term that denotes the total number of menstrual cycles a woman experiences in her lifetime. With increased menstrual cycles, the woman’s exposure to estrogen and progesterone also increases. These hormones circulate the breast tissues and increase the risk of developing breast cancer.
Therefore, the number of menstrual cycles a woman has is a risk factor for developing breast cancer.
Studies show that women who have regular and shorter menstrual cycles have a higher risk for breast cancer than those with longer cycles.
These studies also report that women who had more menstrual cycles before their first full-term pregnancy were at higher risk for breast cancer.
A population-based study analyzed the relationship between the number of menstrual cycles a group of 6718 women had before menopause and their risk of breast cancer. The study reports that women who had more menstrual cycles and hence more exposure to estrogen were at higher risk for breast cancer.
Age Of Menarche And Breast Cancer Risk
With early menarche, women have increased exposure to estrogen and progesterone. For instance, assuming the menopausal age to be 50, a woman with a menarche age of 11 has a 39-year exposure to the hormones. On the other hand, another woman with a menarche age of 17 only has a 33-year exposure to the hormones.
A study analyzed serum estrone (E1) and estradiol (E2) levels in postmenopausal women. The study shows that women with a late menarche age (later than 17 years) had significantly lesser amounts of E1 and E2 levels after menopause. This brought down their risk of breast cancer.
A meta-analysis studied the relationship between menarche age and risk of breast cancer in 118,964 women with a breast cancer diagnosis across 117 studies. According to the meta-analysis, breast cancer risk increases slightly for each year earlier menstruation begins (by about 5%).
Another study reported that women with a menarche age of 11 or lower had a 15-20% higher chance of developing breast cancer than women with a menarche age of 15 or higher.
Age Of Menarche & Breast Cancer Risk: Genetic Factors
Changes in the functioning of specific genes (genetic polymorphisms) can increase or decrease the menarche age and, as a result, increase or decrease the risk of breast cancer.
The INHBA Gene
The INHBA gene (Inhibin, beta A gene) helps produce the INHBA protein. This protein plays a role in controlling the production of the Follicle-Stimulating Hormone (FSH). FSH increases and decreases during each menstrual cycle and plays a role in the maturation of the reproductive system.
rs1079866 is a single nucleotide polymorphism or SNP in the INHBA gene. It has been associated with breast cancer risk. The C allele of this SNP has been associated with lower age of menarche and increased risk of breast cancer.
In women with a lower menarche age, the SNP rs1079866 of this gene showed an increased risk of developing breast cancer. People with this SNP had a per-risk-allele odds ratio of 1.14.
The PXMP3 Gene
The PXMP3 gene helps produce the PXMP3 protein (peroxisomal membrane protein 3). The A allele of the SNP rs7821178 is associated with a higher risk of breast cancer in women with early menarche ages.
The LEP Gene
The LEP gene helps produce a hormone called leptin. Leptin is responsible for maintaining body weight and controlling fat stores. Leptin also plays a role in fertility and the initiation of puberty.
People with the AA genotype of the SNP rs7799039 of this gene have early menarche and an increased risk of breast cancer.
Recommendations To Reduce Breast Cancer Risk
Maintain a healthy weight from a younger age
Studies show an inverse relationship between Body Mass Index (BMI) levels and menarche age. Younger girls who fall under the overweight and obese categories get their first menstrual cycle very early. This can increase the risk of breast cancer in girls as they grow up. Maintaining healthy BMI levels from a very young age can help women lower breast cancer risk.
Be Physically Active
Girls who were physically active as they grew up have significantly delayed menarcheal age compared to girls who did not have much physical activity. A Canadian study reports that girls who participated in dance, swimming, figure skating, and diving competitions had a lower risk of reaching early menarcheal age. Adequate physical activity will help bring down the risk of breast cancer as the girls grow up.
Avoid Exposure to Tobacco Smoke
A 2004 study analyzed the effects of tobacco smoke exposure in little girls and their menarcheal age. According to the study, girls who had high exposure to prenatal smoke and secondhand smoke had early menarche compared to girls who were not exposed to tobacco smoke.
Early menarche age and the inhalation of carcinogenic chemicals from tobacco smoke can both increase the girl’s risk of breast cancer when she grows up.
Increase Plant Food Intake
A small-scale study analyzed the effects of nutrition on menarche age. According to the study, girls who consumed more animal proteins than plant proteins between the ages of 3 and 5 had earlier menarche.
Another study reported that girls who consume isoflavones, a type of isoflavonoid (plant compound) produced by the bean family, experience slightly delayed menarche. Soybeans, chickpeas, peanuts, and pistachios are rich in isoflavones.
Summary
- Menarche is the age at which the first menstrual cycle occurs. This is the main event for puberty and the maturation of the female reproductive system.
- Menstrual cycles cause an increase in the steroid hormones estrogen and progesterone in the female body. Increased lifetime menstrual cycles in a woman increases her exposure to these hormones and increases the risk of breast cancer.
- Early menarche also increases a woman’s lifetime exposure to estrogen and progesterone, increasing the risk of breast cancer.
- Changes in the INHBA gene, PXMP3 gene, and LEP gene can all increase or decrease the menarche age and, therefore, increase or decrease the risk of breast cancer.
- Maintaining healthy BMI levels, getting adequate physical activity, and staying away from tobacco smoke can all help delay menarche age and reduce breast cancer risk.
References
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3488186/
- https://en.wikipedia.org/wiki/Menarche
- https://breast-cancer-research.biomedcentral.com/articles/10.1186/s13058-020-01326-2
- https://www.cdc.gov/cancer/breast/basic_info/risk_factors.htm
- https://pubmed.ncbi.nlm.nih.gov/9752986/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4166004/
- https://pubmed.ncbi.nlm.nih.gov/22364156/
- https://medlineplus.gov/genetics/gene/lep/#conditions
