Current research indicates that vitamin D is more protective than preventative when it comes to most cancers. That is, if an individual has cancer, higher 25(OH)D levels may extend their life. This was recently confirmed in a study from Australia of about 1,200 elderly women who were followed for about ten years after having their baseline 25(OH)D measured in 1998.
Figure 1: Adjusted hazard ratios for death from cancer across continuous measures of serum 25(OH) D concentrations
The researchers found that death from cancer decreased by 33% for every 12 ng/ml (30nmol/l) increase in 25(OH)D. They also analyzed the cancer mortality risk by comparing those with very low serum 25 (OH) D concentrations (less than 18 ng/ml; 45 nmol/l) to those with baseline serum 25 (OH) D concentrations greater than 33 ng/ml (82.5 nmol/l). They found an increased risk of cancer death by at least 2.6 fold among those with very low serum 25 (OH) D concentrations (HR: 2.63; p = 0.04).
The authors did not want to say what their study actually showed, which was the association between death from cancer and baseline 25(OH)D. These findings were linear without evidence of a cut-off at 20 or 30 ng/ml.
The take away message from this study is that if you have cancer, higher vitamin D levels may extend your life.
Like all such studies, this one was limited to only one 25(OH)D measurement, at baseline. So we don’t know how the women’s vitamin D levels changed over the duration of the study. Also, this was not a randomized controlled trial of vitamin D supplementation; therefore, we don’t know whether supplementing with vitamin D will extend your life if you have cancer. Like all such decisions, it is a risk vs. benefit analysis. The risk of having a low 25(OH)D appears to be real. The risk of taking 10,000 IU/day if you have cancer appears to be very low, while the benefits may be very large.
However, keep something in mind: everyone who takes vitamin D supplements will die. It is just a question of when.