{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,21]],"date-time":"2026-01-21T01:53:55Z","timestamp":1768960435996,"version":"3.49.0"},"reference-count":30,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2026,1,20]],"date-time":"2026-01-20T00:00:00Z","timestamp":1768867200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["JCM"],"abstract":"<jats:p>Background: Vitamin D deficiency has been implicated in breast cancer pathogenesis and prognosis. However, the relationship between serum 25-hydroxyvitamin D [25(OH)D] levels and molecular breast cancer subtypes remains incompletely understood. Methods: This cross-sectional study included 168 women (89 breast cancer patients, 79 healthy controls) from Poland. Serum 25(OH)D was measured by electrochemiluminescence immunoassay. Blood samples were collected year-round, with 54% obtained during winter\/spring months (October\u2013March). Molecular subtypes (luminal A, luminal B, HER2-enriched, triple-negative) were classified by immunohistochemistry. Results: Mean 25(OH)D was 30 \u00b1 13 ng\/mL, with 55% showing insufficiency (&lt;30 ng\/mL). No significant differences were observed between patients and controls (p = 0.93). A borderline non-significant trend was observed across molecular subtypes (p = 0.055). HER2-enriched tumors showed descriptively higher concentrations (37.6 ng\/mL, 95% CI: 29.5\u201345.8) compared to luminal A (31.0 ng\/mL), luminal B (26.4 ng\/mL), and triple-negative (25.9 ng\/mL). A significant subtype \u00d7 season interaction was detected (p = 0.015), though interpretation is limited by the absence of a main seasonal effect (p = 0.64). Age (OR = 1.06, p = 0.023) and BMI (OR = 1.06, p = 0.090) predicted vitamin D deficiency. Conclusions: Vitamin D insufficiency is prevalent in breast cancer patients and healthy women. In this exploratory analysis with limited statistical power, no definitive associations between 25(OH)D and molecular subtype were established. The descriptive trend suggesting higher vitamin D in HER2-enriched tumors requires validation. Limitations: Small sample sizes (n = 11\u201335 per subtype) and post-surgical blood collection limit interpretation; findings require validation in larger cohorts.<\/jats:p>","DOI":"10.3390\/jcm15020833","type":"journal-article","created":{"date-parts":[[2026,1,20]],"date-time":"2026-01-20T13:02:07Z","timestamp":1768914127000},"page":"833","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Serum 25-Hydroxyvitamin D Levels in Breast Cancer Patients: A Cross-Sectional Analysis by Molecular Tumor Subtypes"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7616-789X","authenticated-orcid":false,"given":"Dorota","family":"Weber","sequence":"first","affiliation":[{"name":"Institute of Human Sciences, WSEI University, 20-209 Lublin, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2461-0300","authenticated-orcid":false,"given":"Andrzej","family":"Stanis\u0142awek","sequence":"additional","affiliation":[{"name":"St. John of Dukla Centre of Oncology of Lublin Region, 20-090 Lublin, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4446-2592","authenticated-orcid":false,"given":"Anna","family":"Irzma\u0144ska-Hudziak","sequence":"additional","affiliation":[{"name":"Institute of Health Sciences, Catholic University of Lublin, 20-950 Lublin, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8426-9546","authenticated-orcid":false,"given":"Teresa","family":"Kulik","sequence":"additional","affiliation":[{"name":"Institute of Human Sciences, WSEI University, 20-209 Lublin, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1371-4008","authenticated-orcid":false,"given":"Anna Beata","family":"Pacian","sequence":"additional","affiliation":[{"name":"Department of Health Education, Faculty of Nursing Development, Medical University in Lublin, 20-059 Lublin, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2321-9999","authenticated-orcid":false,"given":"Monika","family":"Bary\u0142a-Matejczuk","sequence":"additional","affiliation":[{"name":"Institute of Human Sciences, WSEI University, 20-209 Lublin, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4578-8722","authenticated-orcid":false,"given":"Marta","family":"\u0141uczyk","sequence":"additional","affiliation":[{"name":"Department of Long-Term Care Nursing, Faculty of Health Sciences, Medical University of Lublin, 20-093 Lublin, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0889-6326","authenticated-orcid":false,"given":"Robert","family":"\u0141uczyk","sequence":"additional","affiliation":[{"name":"Department of Internal Medicine and Internal Nursing, Faculty of Health Sciences, Medical University of Lublin, 20-059 Lublin, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,1,20]]},"reference":[{"key":"ref_1","first-page":"233","article-title":"Cancer statistics, 2023","volume":"73","author":"Siegel","year":"2023","journal-title":"CA Cancer J. 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