The study shows that a daily dose of 4,000 IU – 8,000 IU vitamin D reduces cancer progression by up to 36%. The study had 2 phases, the first one used 4,000 IU vitamin D daily and the second one used 8,000 IU daily. Both phases reported robust benefits, and also noted something Peat has been mentioning to people over email – overweight/obese people have trouble raising serum vitamin D levels even when taking large doses. So, for those people a daily dose in the 8,000 IU – 10,000 IU range may be needed. Another study linked below looked at the effects of vitamin D on all types of GI cancers and also found benefit from doses as low as 2,000 IU daily, with higher doses being more beneficial.
https://www.medpagetoday.com/hematologyoncology/coloncancer/79139
https://ascopubs.org/doi/abs/10.1200/JCO.2017.35.15_suppl.3506
“…Results of a small clinical trial suggest that supplementing chemotherapy with high doses of vitamin D may benefit patients with metastatic colorectal cancer by delaying progression of the disease, say scientists from Harvard-affiliated Dana-Farber Cancer Institute. Prompted by the “very encouraging” results of the Sunshine clinical trial, the potential benefits of vitamin D supplementation in metastatic colorectal cancer will be evaluated in a larger clinical trial planned to open at several hundred sites across the U.S. later this year, said Kimmie Ng, director of clinical research in Dana-Farber’s Gastrointestinal Cancer Center, and corresponding author of the Sunshine study. “To our knowledge, this study is the first completed randomized clinical trial of vitamin D supplementation for treatment of advanced or metastatic colorectal cancer,” Ng said. In the high-dose group, patients had a median delay of 13 months before their disease worsened; in the low-dose group, the median delay was 11 months. In addition, patients in the high-dose vitamin D group were 36 percent less likely to have disease progression or death during the follow-up period of 22.9 months. The trial included too few patients to determine whether those who took high-dose vitamin D survived longer overall. “The results of our trial suggest an improved outcome for patients who received vitamin D supplementation, and we look forward to launching a larger trial to confirm these exciting and provocative findings,” said Charles Fuchs, formerly of Dana-Farber and now director of Yale Cancer Center, the senior author of the study.”
“… The Sunshine trial randomized 139 patients with previously untreated metastatic colorectal cancer. One group took pills containing 4,000 international units (IU) of vitamin D per day along with standard chemotherapy, while the other group took 400 units (about the dose found in a multivitamin) along with chemotherapy. “
“… Against this backdrop, the randomized, prospective phase 2 Sunshine trial recruited patients at 11 academic and community centers across the U.S. to test whether vitamin D supplementation can improve outcomes in patients with metastatic colorectal cancer. All patients received standard chemotherapy. Patients in the high-dose vitamin D group initially took 8,000 IU a day for 14 days, then 4,000 IU a day thereafter. The low or standard-dose vitamin D group took 400 IU daily during all cycles. All patients were asked not to take any other vitamin D or calcium supplements during the trial period. “
“…Analysis of the results showed less benefit from high-dose vitamin D in patients who were obese, and those whose tumors contained a mutated KRAS gene, suggesting “that certain subsets of patients may need even higher doses of vitamin D for anti-tumor activity,” the researchers said. They cautioned, however, that high doses of vitamin D shouldn’t be taken except within the context of a clinical trial.”
