Low serum vitamin D levels have been associated with risk for carcinomas of the breast, prostate and colon in epidemiological studies. Non-skeletal actions of vitamin D have gained interest in research, particularly in the field of oncology. 1 2 Values <20 ng/ml have been traditionally considered deficient (in accordance with the latest Institute of Medicine guidelines), whereas values <30 ng/ml have been suggested to be suboptimal. 1 However, the definition of normal circulating vitamin D levels is debatable. 1 Levels of 25-hydroxyvitamin D are relatively stable and can be measured to determine the vitamin D status of a patient. 1 Production of 1,25-dihydroxyvitamin D is tightly regulated by the parathyroid glands in response to calcium. 1 25-Hydroxyvitamin D is the major circulating form of vitamin D and undergoes hydroxylation in the kidney to 1,25-dihydroxyvitamin D, the most active metabolite. Vitamin D, obtained through the diet, supplementation and sunlight, is converted to 25-hydroxyvitamin D in the liver. Strengths include a community-based sample in both primary care and oncology patients and control of age, body mass index, latitude, time and season of blood draw and geographical region of both patient groups. Limitations include a relatively small sample size, lack of data on comorbid conditions of the primary care group, lack of data on vitamin D measurement and lack of data on supplementation or treatment that may have affected vitamin D levels. Providers caring for cancer patients should be aware of an increased incidence of hypovitaminosis D at the community level. Our findings of low vitamin D among the oncology patients add practical relevance to this association since we analysed patients at community clinics. Multiple levels of evidence suggest an association between low vitamin D and cancer. Our study sought to analyse vitamin D levels in large outpatient oncology and primary care centres.
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