For years, the morning routine has been the same for millions of people: a glass of water, one small capsule of vitamin D. The claims have piled up beside it — stronger bones, a calmer immune system, a healthier heart. And the biggest claim of all: vitamin D as cancer protection.
In September, a phase 3 trial published in JAMA poured cold water on that final claim.
The trial that said no
SOLARIS (Alliance A021703) randomized 455 patients with previously untreated metastatic colorectal cancer. Everyone received standard chemotherapy plus bevacizumab. Half also received high-dose vitamin D3; the other half received standard-dose vitamin D3. The question was simple: would the higher dose slow the cancer down?
After a median follow-up of 20 months, the answer was no. Median progression-free survival was 11.8 months with high-dose vitamin D3 versus 10.3 months with standard-dose vitamin D3 — a difference that never reached statistical significance (HR, 0.92; 95% CI, 0.73–1.16; P = .25). Objective response rates (51% vs 44%) and overall survival were equally unmoved. A possible benefit in patients with left-sided tumors remains hypothesis-generating, not proof.
Why vitamin D drew so much hope
Vitamin D is not an ordinary nutrient. The skin makes it from sunlight, and the liver and kidneys convert it into a steroid hormone that reaches far beyond calcium and bone. Cells across the body carry receptors for it, and laboratory studies have long suggested it can restrain cell growth and shape immunity. That made vitamin D3 a natural candidate for an old drug with new tricks — and a favorite topic in cancer research.
The earlier hope had a name: SUNSHINE. In 2019, that phase 2 trial reported a supportive hazard ratio suggesting high-dose vitamin D3 might extend progression-free survival in metastatic colorectal cancer, with a median of 13.0 months versus 11.0 months. The signal was promising enough to justify the larger, definitive test.
Why a phase 3 verdict matters
This is why SOLARIS matters. Phase 2 signals are famous for fading in bigger confirmatory trials: patient groups change, controls tighten, and early hope meets statistics. SOLARIS was that confirmatory test, and it did not reproduce the signal. "Old drug, new use" is not dead, but it now carries a heavier burden of proof.
