Abstract
506
Background: Birthweight, adult waist circumference and age at menarche have independently been associated with breast cancer risk. In addition, the etiologic role of endogenous hormones, such as 17β-estradiol, in relation to breast cancer risk is strongly supported. Thus, we hypothesize that birthweight, in combination with energy status later in life, may influence premenopausal hormonal levels over an entire menstrual cycle. Methods: Among 204 healthy women, aged 25-35 years, who participated in the Norwegian EBBA I Study, birthweight and age at menarche were assessed by questionnaire, personal health record and interview. Levels of 17β-estradiol were measured in daily saliva samples over one menstrual cycle using radioimmunoassay (RIA). Measurements of body composition, including waist circumference (cm) were made. Fasting blood samples were drawn. Results: The women reported a mean birthweight of 3389 g, birth length 50.1 cm and age at menarche 13.1 years. We found that women with lower birthweights, combined with large waist circumference during adulthood, had higher levels of free 17β-estradiol over an entire menstrual cycle compared with women with high birthweights and large waist circumference. Women with birthweights < 3530 g, who later developed large waist circumference (waist ≥ 84 cm), showed 32% higher 17β-estradiol concentrations over a menstrual cycle compared with women with higher birthweights (≥ 3530 g) and large waist circumference (p = 0.03). The association was even more pronounced in women with birthweights < 3220 g and early age at menarche (< 12 years) and adult large waist circumference that is possibly important for breast cancer risk. Conclusion: Our findings support possible variation of premenopausal levels of 17β-estradiol in response to birthweight and energy status in adult life, suggesting that women of lower birthweights may have a different set point for their physiological responsiveness to later obesity than women with higher birthweights. This may influence estradiol levels during each menstrual cycle and is possibly important for breast cancer risk.
99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA