Here is some potential good news for those worried about being (or having been) overweight in young adulthood. The bottom line: being fatter in early adulthood may lead to reduction breast cancer risk before menopause.
Finding: In this large pooled analysis of data on 758 592 premenopausal women, an inverse association of breast cancer risk with body mass index at 18 through 54 years of age was found, most strongly for body mass index at ages 18 through 24 years. The inverse association was strongest for hormone receptor–positive breast cancer, was evident across the entire distribution of body mass index, and did not materially vary by attained age or other characteristics of women.
Meaning: Increased adiposity (fat), in particular during early adulthood, may be associated with reductions in the risk of premenopausal breast cancer.