Abstract Background: Recent evidence suggests a role for vitamin D in breast cancer etiology and survival. Although data are not definitive, breast cancer survivors might derive additional benefits from adequate vitamin D levels, including better quality-of-life (QoL) and psychosocial well-being. Objective: Using a prospective study design, we examined associations between QoL and psychosocial functioning among breast cancer survivors and circulating 25(OH)D levels at the time of initial breast cancer diagnosis and 1 year post diagnosis. Methods: Women (n=504) with incident breast cancer (stages 0-III) were recruited prior to initiating breast cancer treatment at Roswell Park Cancer Institute (RPCI), with 372 patients also providing data 1 year later. Demographic and clinical data were obtained from the RPCI Surgical Oncology Breast Database. At each time point, participants provided blood samples and completed surveys on mental and physical health (SF36 Health Survey), perceived stress (Perceived Stress Scale), depression (Center for Epidemiologic Studies Depression Scale), and their experiences with fatigue (Multidimensional Assessment of Fatigue Scale). Serum 25(OH)D levels were measured by immunochemiluminometric assays. Results: Median 25(OH)D levels at diagnosis and 1 year post were 23.8 ng/ml (range 0.1-67.4) and 26.6 ng/ml (range 3.0 – 80.0), respectively. At the time of diagnosis, multivariate logistic regression analyses indicated that women with sufficient levels of 25(OH)D (≥ 30 ng/ml) had ∼50% lower odds of reporting poor physical health (OR=0.52, 95% CI: 0.29, 0.90) or poor mental functioning (OR=0.54, 95% CI: 0.31, 0.95) compared to women with deficient levels (<20 ng/ml). Women with higher 25(OH)D were also less likely to report high levels (>median) of perceived stress (OR=0.45, 95% CI: 0.26-0.80), depression (OR=0.46, 95% CI: 0.25-0.83) or fatigue (OR=0.54, 95% CI: 0.31, 0.92). Findings were similar 1 year later, with reduced odds of poor physical health (OR=0.47, 95% CI: 0.24-0.93), poor mental health (OR=0.62, 95% CI: 0.33, 1.13), high levels of perceived stress (OR=0.67, 95% CI: 0.36, 1.25), depression (OR=0.33, 95% CI: 0.15, 0.71), and fatigue (OR=0.45, 95% CI: 0.24, 0.84). Changes in vitamin D levels over the 1 year period were also assessed. While none of the relationships were significant, women in the upper tertile of vitamin D change (>3.99 ng/ml) were more likely to report low mental health and higher levels of perceived stress at 1 year compared to patients with declines in 25(OH)D of >0.95 ng/ml, but were less likely to report poor physical health or fatigue. This may have been due, in part, to women being somewhat more likely to use vitamin D supplements if they reported lower mental health QoL scores. Changes in circulating 25(OH)D levels during this 1 year period were strongly associated with use of supplements (p=0.001). Conclusions: Breast cancer survivors with adequate vitamin D levels were less likely to report poor QoL compared to women with deficient vitamin D levels. Maintenance of optimal vitamin D levels may help improve breast cancer patients’ QoL as they go through breast cancer treatment. Citation Format: Chi-Chen Hong, Song Yao, Yali Zhang, Shicha Kumar, Christine Ambrosone. High serum levels of 25-hydroxyvitamin D are associated with better quality-of-life, and lower levels of perceived stress, depression, and fatigue among breast cancer survivors [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-09-27.