Association between BMI, vitamin D, and estrogen levels in postmenopausal women using adjuvant letrozole: a prospective study

• Published in: NPJ breast cancer 2020-06, Vol.6 (1), p.22
• Main Authors: Elliott, Mitchell J, Ennis, Marguerite, Pritchard, Kathleen I, Townsley, Carol, Warr, Dave, Elser, Christine, Amir, Eitan, Bedard, Philippe L, Rao, Lakshmi, Stambolic, Vuk, Sridhar, Srikala, Goodwin, Pamela J, Cescon, David W
• Format: Article
• Language: English
• ISSN: 2374-4677; 2374-4677

Studies have suggested that women with elevated BMI or 25-OH vitamin D levels may derive less benefit from AIs versus tamoxifen. We prospectively investigated whether high BMI or 25-OH vitamin D levels were associated with higher estrogen levels in post-menopausal women receiving standard adjuvant letrozole (2.5 mg/day). Furthermore, we evaluated whether an increased dose of letrozole resulted in lower serum estrogens in women with BMI > 25 kg/m . Correlation between entry BMI and day 29 serum biomarkers (estrogens, 25-OH vitamin D, insulin, CRP, leptin) was assessed in all patients. On day 29, participants with BMI > 25 kg/m switched to letrozole 5 mg/day for 4-weeks and blood was drawn upon completion of the study. The change in serum estrogen levels was assessed in these patients (BMI > 25 kg/m ). 112 patients completed days 1-28. The Pearson correlations of estradiol and estrone with BMI or serum 25-OH vitamin D levels were near zero (-0.04 to 0.07, p = 0.48-0.69). Similar results were obtained for correlation with markers of obesity (insulin, CRP, and leptin) with estradiol and estrone (-0.15 to 0.12; p = 0.11-0.82). Thirty-one patients (BMI > 25 kg/m ) completed the interventional component; Increasing the dose of letrozole did not further reduce estradiol or estrone levels (change 0.1 and 0.4 pmol/L respectively; p = 0.74 and 0.36). There was no observed association between markers of obesity (BMI, insulin, leptin, and CRP), serum 25-OH vitamin D levels and estradiol or estrone levels. Additionally, an increased dose of letrozole did not further reduce estradiol or estrone levels compared to the standard dose.