The news that a study found that Vitamin D decreased cancer risk by as much as 60% was impressive and widely touted as a proven means of preventing cancer.
The researchers at Creighton University in Omaha focused on 1,179 seemingly healthy women with an average age of 67. The women were divided into three groups: 446 got calcium and vitamin D3 supplements, a similar number got calcium alone, and 288 took dummy pills.
The research team gave 1,000 daily international units of vitamin D, more than current guidelines calling for 200 to 600 units depending on a person’s age.
The researchers intended to check mainly for the effects of calcium on bone health. Their interest in cancer risk was secondary.
But the lower cancer risk stood out. Only 13 women, or 3 percent, developed cancer over four years of calcium and vitamin D supplements. With calcium alone, 17 women, or 4 percent, got cancer. With dummy pills, cancer appeared in 20 women, or 7 percent.
That shows a 60 percent lower cancer risk over four years in the group taking both supplements, compared to patients taking placebos. And when the first-year cancers were excluded – the ones mostly likely present before the study began – the findings were stronger still: a 77 percent lower risk for the combo group.
A study with 1179 people divided into three groups is very small. The numbers of cancers in the groups 13 vs 17 vs 20 are interesting particularly because of the different group sizes but in my view not conclusive. The occurrence of cancer in 7% of the placebo group over the 4 years of the study seems higher than the population at large and may indicate a problem with patient selection, rather than a protective effect from the vitamin D.
More work needs to be done before people run out and start taking doses of Vitamin D and calcium because as with all biologically active treatments there are risks–high blood levels of calcium and kidney stones come to mind immediately.