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High-Dose Vitamin D3 Did Not Slow Colorectal Cancer in Trial

A phase 3 clinical trial published in JAMA on 3 August 2026 has found that high-dose vitamin D supplements, added to standard chemotherapy, did not slow disease progression in patients with metastatic colorectal cancer. The SOLARIS trial (Alliance A021703), led by Dr Kimmie Ng of the Dana-Farber Cancer Institute and Harvard Medical School, randomised 455 patients with previously untreated metastatic colorectal cancer at cancer centres across the US National Clinical Trials Network between October 2019 and December 2022. Patients received standard chemotherapy plus bevacizumab, combined with either a high dose of vitamin D3 (an 8,000 IU daily loading dose for 14 days, then 4,000 IU daily) or a standard dose of 400 IU daily. Median progression-free survival was 11.8 months in the high-dose group against 10.3 months in the standard-dose group, a difference the researchers said was not statistically significant. Overall survival and response rates also showed no meaningful difference between the two groups, according to the published results.

Why an earlier, smaller trial pointed the other way

The SOLARIS trial was designed to confirm results from an earlier phase 2 trial that had suggested high-dose vitamin D supplements improved progression-free survival in the same patient group. It did not replicate that finding at phase 3 scale. The trial did find a possible benefit for high-dose vitamin D3 in the subgroup of patients with left-sided tumours, which the researchers described as worth further investigation rather than a confirmed effect. No additional safety concerns were reported with the higher dose. The trial was funded through the National Cancer Institute's National Clinical Trials Network, with vitamin D3 supplied by Pharmavite.

What this means for your supplement routine

This trial tested vitamin D3 as an addition to cancer treatment at doses and in a patient group with no relevance to a general supplement routine, and the researchers were explicit that high-dose vitamin D3 cannot be recommended on this evidence for treating colorectal cancer. It is a reminder that a nutrient's role in one context, such as normal immune or bone function, does not carry over to unrelated claims about disease outcomes. Anyone comparing prices on the vitamin D products already in their cupboard can do so in the vitamins and minerals collection.

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This article reports published news and research and is for information only. Food supplements are not a substitute for a varied diet or medical care, and no product mentioned is intended to diagnose, treat, cure or prevent any disease. Speak to your GP or pharmacist before changing what you take, especially if you are pregnant, breastfeeding, or taking prescribed medicines.

Sources

Originally reported by JAMA. This article has been reviewed by Dr Tosin.

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