Advantage of daily vitamin D administration
At first glance, when all 14 identified placebo-controlled, randomized intervention studies with a total of 104,727 subjects were evaluated together, the results may be disappointing: Vitamin D substitution reduced the risk of dying from cancer in the general population by only 6 percent. However, the correlation did not reach statistical significance. Study participants took vitamin D for one to seven years3 either one daily (400 to 4000 IU) or monthly (60,000 IU) or every four months (100,000 IU) high doses. Two studies looked at an initial bolus dose followed by daily intake of the vitamin. When the researchers included only the 10 studies in which participants took colecalciferol daily, vitamin supplementation reduced cancer mortality by a statistically significant 12 percent (p=0.019), while the remaining four bolus studies did not achieve any mortality reduction.
The authors see regular bioavailability as the reason for this advantage of daily administration. Daily intake counteracts the rapid excretion of the vitamin and prevents imbalances in the metabolism of the vitamin.