Several recent studies attempted to determine the role of vitamin D supplementation in oncogenesis and cancer treatment. The relationship, however, remains unclear.

A study in the Journal of Clinical Oncology showed, for example, that a deficiency of serum 25-hydroxyvitamin D (25-OH D) increased the odds of adverse prostate cancer pathology among men with localized prostate cancer undergoing radical prostatectomy.1 Serum 25-OH D levels less than 30 ng/mL were associated with more than twice the risk of adverse pathology.

A systematic review of 7 studies of vitamin D and bladder cancer showed that vitamin D deficiency increased the risk of developing the disease (this was found in 5 of the 7 studies).2 Higher levels of vitamin D correlated with better survival and outcomes.

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A pooled analysis published in PLoS One showed that 25 OH D concentrations of 40 ng/mL or greater were associated with a substantial risk reduction of all invasive cancers.3 The analysis used data from 2 cohorts including more than 2300 people with multiple cancer types. Women with concentrations of 40 ng/mL or greater had a 67% lower risk for cancer than women with concentrations less than 20 ng/mL.

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Other studies have evaluated the role of vitamin D after a cancer diagnosis. JAMA Oncology recently published the results of a cohort study of 1666 women with breast cancer measuring the level of vitamin D in the blood at the time of breast cancer diagnosis.4 Higher serum 25-OH D levels were independently associated with better outcomes for patients, including longer overall survival. Compared with the lowest tertile of vitamin D levels, those women with the highest levels had a superior overall survival; this advantage was even greater among premenopausal women.