Does vitamin D prevent cancer? Chart from 2017 Research Paper

The red line in this chart is the best fit curve to all the data points from Dr. Joan Lappe’s latest randomized controlled trial. You can see that as vitamin D levels increase, moving from left to right, the risk of cancer decreases.

The black lines are confidence bands. If you remember statistics in high school, these are based on standard deviation — it is a measure of how ‘confident’ you are in the line. If there are many data points in a region you are a lot more ‘confident’ than if there are few data points. In this study, most participants had vitamin D levels in the center range where you can see the confidence bands are close to the center line; just a few participants had very low or very high levels where you can see the confidence bands are farther away from the center line.

Participants with a vitamin D level of 55 ng/ml (137 nmol/L) were 35% less likely to get cancer as compared to those with a vitamin D level of 30 ng/ml (75 nmol/L) with a p-value of .03.