Physical activity appears to be inversely related to risk of breast cancer, yet the results remain inconsistent. To evaluate this relation among premenopausal women and examine variation in risk according to level of obesity and use of oral contraceptives (OCs), the authors examined data from the Nurses' Health Study II. During 10 years of follow-up, 849 cases of invasive premenopausal breast cancer were confirmed. Physical activity was assessed by self-report at baseline and during follow-up using a validated questionnaire. Total physical activity was unrelated to risk of breast cancer. Women engaging in X27 metabolic equivalent (MET)-h week À1 had a multivariate-adjusted relative risk (RR) of 1.04 (95% confidence interval (CI) 0.82 -1.33) compared to those in the o3 METh week À1 category. Among women with a BMI X30 kg m À2 , we observed a significant positive dose -response relation (P ¼ 0.04). Activity was unrelated to breast cancer risk at lower levels of BMI. A test for interaction between activity and BMI (o30, X30 kg m À2 ) was statistically significant (P ¼ 0.02). Among current OC users, higher activity was associated with a non-significantly lower risk of breast cancer (RR ¼ 0.59, 95% CI 0.30 -1.16 for X27 vs o9 MET-h week À1 , P for linear trend ¼ 0.14). These results show no overall association between physical activity and risk of breast cancer among premenopausal women, but suggest that the effect of physical activity could be substantially modified by the underlying degree of adiposity. The potential interactions between physical activity, adiposity, and current use of OCs require further study. The relation of physical activity to risk of breast cancer has been assessed by the International Agency for Research on Cancer, which concluded that, although studies have not been entirely consistent, the overall results support a reduction in risk with higher levels of activity (International Agency for Research on Cancer, 2002). The majority of studies, however, have been focused on postmenopausal breast cancer. Also, upon review of more than 30 studies, it was noted that the most important time periods in life for activity is not currently known. Furthermore, which activities may offer the greatest protection have not been systematically examined.In a previous analysis of the Nurses' Health Study II (NHSII) cohort with 372 cases among predominantly premenopausal women, Rockhill et al (1998) observed no association between nonoccupational activity levels in late adolescence or the recent past and risk of breast cancer. We now extend that analysis, adding 477 additional premenopausal cases in an effort to understand better the relation between physical activity and risk of premenopausal breast cancer.In addition to evaluating the type of physical activity, we examined the relation between activity and breast cancer within subgroups of adiposity and oral contraceptive (OC) use, which we hypothesised, might modify the relationship. Potential health effects of (OCs) were the original focus of the NHS II coh...

We examined compliance with and the effects of melatonin supplementation on breast cancer biomarkers (estradiol, insulin-like growth factor I (IGF-1), insulin-like growth factor binding protein 3 (IGFBP-3), and the IGF-1/IGFBP-3 ratio) in postmenopausal breast cancer survivors. In a double-blind, placebo-controlled study, postmenopausal women with a prior history of stage 0-III breast cancer who had completed active cancer treatment (including hormonal therapy) were randomly assigned to either 3 mg oral melatonin (n=48) or placebo daily for 4 months. Plasma samples were collected at baseline and after completion of the intervention. The primary endpoints were compliance and change in estradiol and IGF-1/IGFBP-3 levels. 95 women were randomized (48 to melatonin and 47 to placebo). 86 women (91%) completed the study and provided pre and post intervention bloods. Melatonin was well-tolerated without any grade 3/4 toxicity and compliance was high (89.5%). Overall, among postmenopausal women with a prior history of breast cancer, a 4 month course of 3 mg melatonin daily did not influence circulating estradiol, IGF-1, or IGFBP-3 levels. Compliance was comparable between the two groups. Short-term melatonin treatment did not influence estradiol and IGF-1/IGBBP-3 levels. Effects of longer courses of melatonin and among premenopausal women are unknown. The particularly low baseline estradiol levels in our study population may have hindered the ability to detect any further estradiol lowering effects of melatonin.