Background: Multiple myeloma (MM) is a plasma cell malignancy with multi-organ involvement, including renal impairment, anemia, and particularly skeletal complications. Vitamin D plays a crucial role in bone metabolism by promoting calcium absorption and facilitating bone remodeling. Emerging evidence suggests that vitamin D deficiency is common among MM patients and may be associated with poorer clinical outcomes, including reduced survival. However, routine assessment of vitamin D status is not currently incorporated into standard laboratory evaluations for MM patients in Thailand.

Objective: To determine the prevalence of vitamin D deficiency, identify associated risk factors, and evaluate the impact of vitamin D status on clinical outcomes, including bone morbidity, quality of life (QoL), and progression-free survival (PFS) in patients with MM.

Methods: We conducted a cross-sectional study between July 2024 and June 2025 at the outpatient Hematology Clinic, Faculty of Medicine, Chiang Mai University. Patients with a confirmed diagnosis of MM who had not received vitamin D supplementation were enrolled. Patients with a history of other malignancies were excluded. Treatment regimens followed national guidelines, and bisphosphonates were used when not contraindicated. At enrollment, serum 25-hydroxyvitamin D [25(OH)D] levels were measured. Participants completed a vitamin D risk factor questionnaire and the EORTC QLQ-MY20 for QoL assessment. Demographic data, bone morbidity events, and PFS were retrospectively obtained from medical records. The primary outcome was the prevalence of vitamin D deficiency, defined as a serum 25(OH)D level below 20 ng/mL. Secondary outcomes included the bone morbidity (compression fractures and pathologic fractures on imaging), PFS, QoL scores, and associated risk factors for vitamin D deficiency, analyzed using multivariable logistic regression. PFS was defined as the time from initiation of treatment to documented disease progression as determined by either clinical or biochemical relapse.

Results: A total of 66 patients were enrolled with a median age of 62.76 ± 10.55 years; 42% were male. By International Staging System (ISS) staging, 13.64% had stage I, 25.76% stage II, and 60.60% stage III disease. All patients received proteasome inhibitors and/or immunomodulatory agents. The prevalence of vitamin D deficiency was 28.79% (95% confidence interval [CI], 19.00 - 41.03). Patients in the deficiency group were significantly younger(median: 57.68 ± 12.60 years vs. 64.81 ± 8.96 years; p = 0.0119), while other baseline clinical and laboratory parameters were comparable. Patients with deficiency had significantly worse QoL scores (median: 34 vs. 27; p = 0.0017). Compression fractures were more common in the deficient group (52.63% vs. 27.66%; p = 0.054), suggesting a trend toward increased bone fragility, although the rates of pathologic fractures did not differ significantly (10.53% vs. 6.38%; p = 0.621). Age was identified as an independent risk factor for vitamin D deficiency (odds ratio [OR], 0.93; 95% CI, 0.88 - 0.99; p = 0.022), indicating that older age was associated with a lower risk of deficiency. Among the 30 patients who experienced relapse (45.45%), patients with vitamin D deficiency patients had significantly shorter PFS compared to those without deficiency (median: 9.71 months, interquartile range [IQR] 5.52 - 22.18] vs. 19.67 months, IQR 16.56 - 40.01; p= 0.0147).

Conclusion: Vitamin D deficiency was present in nearly one-third of MM patients and was significantly associated with impaired QoL and shorter PFS in relapsed patients. These findings support the potential importance of incorporating routine vitamin D screening and supplementation into the management of patients with MM. Routine screening may also help mitigate skeletal complications, which remain a major cause of morbidity in MM.

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2025
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