Vitamin D Supplementation and Cancer Risk: Still No Clear Benefit

Summary and Comment |
March 30, 2017

Vitamin D Supplementation and Cancer Risk: Still No Clear Benefit

  1. Thomas L. Schwenk, MD

In women who received supplementation, a small decrease in cancer incidence did not quite reach significance.

  1. Thomas L. Schwenk, MD

Despite epidemiologic and biologic reasons to expect that vitamin D might prevent cancer, dietary supplementation studies have shown no benefit. Now, researchers randomized 2303 healthy postmenopausal women in Nebraska (mean age, 65; 99% non-Hispanic white; mean baseline serum 25-hydroxyvitamin D [25(OH)D], 33 ng/mL) to supplementation with vitamin D3 (2000 IU daily) and calcium (1500 mg daily) or placebo. All participants were asked to limit outside supplementation; actual mean daily amounts of outside supplementation plus dietary intake were about 900 IU (vitamin D3) and 1200 mg (calcium) in both groups.

Over 4 years, mean 25(OH)D levels increased to 44 ng/mL in the intervention group and remained constant in the placebo group. The overall incidence of new cancers was not significantly different in the intervention and placebo groups (3.9% vs. 5.6%; P=0.06). However, in a post hoc analysis of study years 2 through 4, the difference barely reached significance (3.2% vs. 4.9%; P=0.048).

Comment

It's not surprising that this trial did not add support for vitamin D in cancer prevention. Short-term supplementation with vitamin D (or calcium) later in life seems unlikely to significantly affect cancer incidence. Also, the participants' relatively high mean baseline 25(OH)D levels and substantial outside supplementation could have blunted any effect. Still, the findings after the first year are intriguing and should be revisited in light of a larger, longer-duration supplementation trial of vitamin D now under way.

Editor Disclosures at Time of Publication

  • Disclosures for Thomas L. Schwenk, MD at time of publication Editorial boards UpToDate

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