The objective of this study was to evaluate the effect of reduced sun exposure of outdoor workers on vitamin D status using different modalities of sun protection, for primary prevention of skin cancer. 25-OH-D3 measurements were performed in two successive winters, 8 (interim) and 20 months after initiation of the study, in three groups of male outdoor workers, enrolled in either a complete, partial or minimal sun protection program. Ambient solar UVB radiation was monitored simultaneously. No intragroup or intergroup differences were observed between the interim- and postintervention measurements of mean 25-OH-D3, which were close to 30 ng mL−1. Significant risk factors for postintervention 25-OH-D3 levels >33.8 ng mL−1 (a surrogate for reduced sun protection) were: previous sunburn episodes (OR 2.5; 95% CI 1.01–6.3; = 0.05) and younger age (OR 0.92; 95 CI 0.86–0.98; = 0.009). Outdoor workers of Western, compared with those of Eastern paternal origin had a borderline significant risk (OR 2.4; 95% CI 0.9–6.3; = 0.07). A borderline significant effect (OR 2.9; 95% CI 0.97–10.1; = 0.085) was also noted for those in the minimal intervention group. In conclusion, sun protection among outdoor workers following a successful intervention did not suppress mean winter 25-OH-D3.