Aim Epidemiological studies suggest an association between vitamin D and calcium intake and breast cancer. The aim of this study was to determine the association of breast cancer with vitamin D deficiency and osteoporosis according to menopausal status and to examine vitamin D and bone mineral density (BMD) levels in breast cancer patients. Methods This was an observational cohort hospital-based study. It included 635 patients with breast cancer. Socio-demographic information, type of consanguinity, menopause status, medical history, lifestyle habits, dietary intake, BMD measurements and vitamin D levels were collected. Descriptive and univariate analyses were performed. Results Of the studied patients, 36.1% were Qataris, 63.9% non-Qatari Arabs, 40% premenopausal women, 20.9% university graduates and 37.2% housewives. Overall, 31.8% of breast cancer women were affected with osteopenia/osteoporosis. Vitamin D deficiency (10.7% vs. 7.9%) and severe vitamin D insufficiency (39.2% vs. 32.5%) were higher in postmenopausal women than premenopausal women (P < 0.001). Low physical activity (< 30 min/day) was observed among vitamin D deficient (46.8%) and osteoporotic (45%) women. Dietary intake of vitamin D was significantly lower in vitamin D deficient women; these included dairy products (33.1%), milk (38.6%), seafood (39.6%), (P < 0.001) and for osteoporotic women, dairy products (46%), calcium (21.3%), milk (36.1%), yoghurt (37.6%), cheese (37.6%) and sea food (34.7%) (P < 0.001). Conclusion The present study findings revealed a high prevalence of vitamin D deficiency and osteoporosis in breast cancer patients. Also, the dietary intake of vitamin D and calcium was significantly lower in breast cancer women.