More is not better: the largest doses came with more falls
One 500,000 international unit dose a year raised falls 15 percent in older women. In another trial 66.9 percent of the highest-dose group fell, against 47.9 percent.
What the study found
The largest doses were followed by more falls, not fewer
One 500,000 international unit dose of vitamin D3 a year raised falls by 15 percent in older women, most in the three months after each dose. In another trial the highest monthly doses reached the target level best, and 66.9 percent of that group fell against 47.9 percent on the lowest.
The caveat · Giant yearly and monthly doses only
Both trials gave very large intermittent doses, so nothing here suggests a daily tablet carries the same risk. The falls trial enrolled 200 people and had no placebo group, comparing one dose against another rather than against nothing. The annual-dose trial's fracture interval starts at exactly no effect, and its explanation for the timing, a spike in blood levels just after each dose, is a hypothesis it raises rather than one it tests.