Serum 25-hydroxyvitamin D and risk of cancer in a large community population under investigation for cardiovascular disease: a retrospective cohort study

OBJECTIVES: It remains unclear whether vitamin D status is related to cancer risk. We examined this relationship using laboratory, administrative and survey data. DESIGN: Retrospective cohort study. SETTING: All care settings within Calgary, Alberta, Canada and surrounding rural communities. PARTICIPANTS: Patients tested for serum 25-hydroxyvitamin D from 2009 to 2013 without a past cancer diagnosis but with an ECG and body mass index ±3 months from testing were included. Age, sex, mean hours of daylight during month of testing were linked to census dissemination area-level indicators of socioeconomic status measured in 2011. PRIMARY AND SECONDARY OUTCOME MEASURES: Hospital discharge diagnoses for any cancer, major cancer (colorectal, breast, lung, prostate, skin) and other cancers >3 months from testing from 2009 to 2016. Cox proportional hazard models were used to examine associations with incident cancer after adjusting for potential confounders. Interactions were tested using multiplicative terms. RESULTS: Among 72 171 patients, there were 3439 cancer diagnoses over a median of 5.9 years. After adjustment, increasing quartile of serum 25-OH vitamin D was significantly associated with an increased risk of any cancer and major cancer, however this was completely driven by an increased risk of skin cancer (Q4 vs Q1: HR=2.56, 95% CI 1.70 to 3.86, p for linear trend <0.01). This association was strengthened among individuals residing in communities with higher proportions of non-citizens, recent immigrants, visible (non-white) minorities and those not speaking an official Canadian language (English or French) at home. CONCLUSIONS: Higher vitamin D status was associated with a greater risk of skin cancer in a large community population under investigation for cardiovascular disease. This association was likely due to sun exposure and may be modified by community variation in vitamin D supplementation.