Why Breast Cancer Is More Common Among Korean Women in Their 40s and 50s: Linked to Slim Body Type

Seven-Year Follow-Up of 4,737 Women in Menopausal Transition
Early Surge in Female Hormones and Breast Density Seen in Underweight Women

A study has found that the relatively slim body type of Korean women may have influenced the fact that breast cancer occurs most frequently among Korean women in their late 40s, which is younger than the peak age for Western women.

The pink ribbon, an international symbol of breast cancer. Pixabay

According to Kangbuk Samsung Hospital on November 19, a joint research team-comprising Professor Ryu Seungho from the hospital’s Healthcare Data Center, Professor Jang Yusu and Dr. Jang Yunyoung from the Cohort Research Center, and Professor Cho Yuseon from the Department of Family Medicine at Asan Medical Center-tracked 4,737 Korean women in the menopausal transition for an average of seven years to examine changes in female hormones and breast density.

The researchers classified the stages of menopause into four categories based on international standards and quantified breast density using an automated analysis program for mammography images. They also divided the participants into four groups according to body mass index (BMI): underweight (<18.5), normal weight (18.5-22.9), overweight (23-24.9), and obese (≥25), and conducted comparative analyses.

The findings showed that underweight women with a BMI below 18.5 experienced a temporary increase in female hormones and breast tissue density during the early stages of the menopausal transition. In contrast, obese women with a BMI of 25 or higher tended to have decreased levels of female hormones and lower breast density.

It is known that breast cancer is influenced by female hormones and that higher breast density increases the risk of developing breast cancer. Therefore, the characteristics observed in underweight women during the early menopausal transition suggest that their risk of developing breast cancer may be relatively higher.

In contrast to White women, whose breast cancer prevalence peaks in their late 60s and beyond, the prevalence among Korean women is highest in their 40s and 50s.

Professor Ryu Seungho explained, "Korean women tend to have a slimmer body type compared to Western women, and this physical characteristic, combined with hormonal changes in the early menopausal period, may be one of the reasons why breast cancer occurs at a younger age than in Western women."

Professor Jang Yusu stated, "This study has demonstrated that the interaction between obesity and hormonal changes may be associated with the timing of breast cancer onset among Korean women. These findings could be used to develop tailored screening and prevention strategies based on body type and hormonal changes before and after menopause."

This research was conducted as part of a project supported by the National Institute of Health under the Korea Disease Control and Prevention Agency, titled "Prospective Study for the Prevention and Management of Chronic Diseases in Menopausal Women." The results were published in the international journal Breast Cancer Research.

Meanwhile, according to the National Cancer Registry Statistics, the number of breast cancer patients in Korea increased nearly fivefold, from 5,890 in 1999 to 29,528 in 2022. It has been the most common cancer among women, showing a continuous increase across all age groups for over 20 years, with a higher proportion of cases occurring in younger women compared to Western countries.