A daily low-dose form of vitamin D3 was more effective on cancer mortality than intake of a monthly high-dose form, especially for adults aged 70 years and older.
Untargeted vitamin D3 was associated with a 12% reduction in cancer mortality, according to the results of a study by investigators at the German Cancer Research Center published in Ageing Research Reviews. A daily, smaller dose of vitamin D appears to have a more significant effect on cancer mortality than infrequent and higher doses, the investigators noted.
"Based on current studies, vitamin D3 supplementation probably does not protect against developing cancer, but it could reduce the likelihood of dying from cancer,” said Ben Schöttker, an epidemiologist at the German Cancer Research Center, in a press release. “However, previous studies on cancer mortality have yielded very different results, and we were interested in the reasons for this."
Vitamin D deficiency is common worldwide, but it is especially common among patients with cancer. Although 15% of German adults sit below the threshold for pronounced vitamin D deficiency (30 nmol/L), prior research suggests that 59% of patients with colorectal cancer are vitamin D3-deficient, which suggests that deficiency is associated with poor prognosis, according to the authors of the current study.
The investigators performed a systematic literature search of high-quality studies to evaluate the efficacy of vitamin D3 on cancer mortality and on survival of patients with cancer. They identified approximately 105,000 participants across 14 studies who had either been randomized into a vitamin D3 or placebo arm.
Investigators pooled the results of the 14 studies and did not observe statistically significant changes on cancer mortality. The team then divided the studies according to dose size and interval length. A daily low dose was 400 to 4000 IU per day, and a higher-dose at longer intervals was 60,000 to 120,000 IU administered once-monthly or less.
The investigators observed that infrequent administration of vitamin D at 60,000 to 120,000 IU had no effect on cancer mortality. In 10 studies that examined the effects of a smaller and frequent dose, vitamin D3 lowered cancer mortality by a statistically significant 12%.
“We can therefore assume that the effect is significantly higher for those people who are actually vitamin D deficient," Schöttker said.
Patients aged 70 years and older appeared to benefit most from daily vitamin D3. Further, daily vitamin D3 intake appears to be most effective against mortality prior to cancer diagnosis.
Investigators reason that vitamin D taken as a daily dose is most effective because it regularly increases the bioavailability of hormone 1,25-dihydroxyvitamin D. This hormone may inhibit tumor growth and prevent cancer mortality, according to Schöttker.
"This work underlines the great potential of vitamin D3 administration in the prevention of cancer deaths,” said Hermann Brenner, an epidemiologist and prevention expert at DKFZ, in the press release. “Regular intake at low doses [400 to 4000 IU per day] is associated with almost negligible risk and very low cost."
German Cancer Research Center. Reduced cancer mortality with daily vitamin D intake. News Release. May 9, 2023. Accessed on May 10, 2023. https://www.eurekalert.org/news-releases/988716.