Serum Total 25-Hydroxyvitamin D Levels in Patients With Cutaneous Malignant Melanoma: A Case-Control Study in a Low-Risk Southern European Population

Causal association between serum 25-Hydroxyvitamin D levels and cutaneous melanoma: a two-sample Mendelian randomization study

Background

Despite numerous observational studies on the association between serum 25-Hydroxyvitamin D levels and cutaneous melanoma, causal inferences remain ambiguous due to confounding and reverse causality. This study aimed to elucidate the causal relationship between serum 25-Hydroxyvitamin D levels and melanoma incidence using Mendelian randomization (MR).

Methods

A two-sample MR was conducted using genetic variants associated with serum 25-Hydroxyvitamin D levels as instrumental variables. Summary statistics for these variants were derived from genome-wide association studies, and those for melanoma risk were obtained from a comprehensive melanoma case-control study. Robustness of the results was assessed through sensitivity analyses, including the "leave-one-out" approach and tests for potential pleiotropy.

Results

The MR analysis provided substantial evidence of a positive causal relationship between serum 25-Hydroxyvitamin D levels and the incidence of cutaneous melanoma, suggesting that each unit increase in serum 25-Hydroxyvitamin D levels corresponds with an increased risk of melanoma. Tests for pleiotropy showed minimal effects, and the sensitivity analysis confirmed no disproportionate influence by any individual single nucleotide polymorphism (SNP).

Conclusion

The findings indicated a potentially causal positive association between serum 25-Hydroxyvitamin D levels and melanoma risk, challenging traditional beliefs about vitamin D's role in melanoma. This emphasizes the need for a balanced and personalized approach to vitamin D supplementation and sun exposure, particularly in high-risk populations. These results should be interpreted with caution due to potential unrecognized pleiotropy and confounding factors. Future research should focus on validating these findings in diverse populations and exploring underlying biological mechanisms.

Prediagnostic serum 25-hydroxyvitamin D and melanoma risk

Previous studies of serum 25-hydroxyvitamin D (25(OH)D) in relation to melanoma have shown conflicting results. We conducted a nested case-control study of 708 cases and 708 controls, using prediagnostically collected serum, to study 25(OH)D and melanoma risk in the population-based Janus Serum Bank Cohort. Stratified Cox regression was used to estimate hazard ratios (HRs) with 95% confidence intervals (CIs) adjusted for ultraviolet radiation (UVR) indicators and stratified by ambient UVB of residence and body mass index (BMI). Non-linear associations were studied by restricted cubic splines. Missing data were handled with multiple imputation by chained equations. We found an HR of melanoma risk of 1.01 (95% CI: 0.99, 1.04) and an HRimputed of 1.02 (95% CI: 1.00, 1.04) per 5-nmol/L increase. The spline model showed exposure-risk curves with significantly reduced melanoma risk between 60 and 85 nmol/L 25(OH)D (reference 50 nmol/L). Non-significant J-shaped curves were found in sub-analyses of subjects with high ambient UVB of residence and of subjects with BMI < 25 kg/m2. Our data did not yield persuasive evidence for an association between 25(OH)D and melanoma risk overall. Serum levels within the medium range might be associated with reduced risk, an association possibly mediated by BMI.

Serum 25-Hydroxyvitamin D Level Is Not Associated with Duration and Activity of Disease in Melanoma Patients

Preclinical and epidemiological studies showed the association between 25-hydroxyvitamin D (vitamin D) and cancer development. The aim of the study was to evaluate serum vitamin D levels of melanoma patients and compare them with other malignancies and healthy controls. A total of 87 cutaneous melanoma patients from a tertiary cancer center were included in the study. Vitamin D levels were measured with electrochemiluminescence binding assay. There were no differences between serum vitamin D levels of melanoma patients, other malignancies and healthy controls (median values: 18.8, 14.3, and 24.5 ng/ml, respectively, p > 0.05). Vitamin D deficiency (<20 ng/ml) was found in 56% of melanoma patients and 42% of healthy controls; however serum vitamin D levels in only 16% of both melanoma patients and healthy controls were sufficient (>30 ng/ml) (p > 0.05). Furthermore, no difference regarding serum vitamin D levels was found between melanoma and other malignancies. Age, gender and clinical stage were not found statistically correlated with serum vitamin D levels. Similarly, serum vitamin D level was not associated with disease duration and presence or absence of active disease. In conclusion, there was no difference between serum vitamin D levels of melanoma patients and healthy controls and it was also not associated with duration and activity of disease.