Dr William Grant, who writes and compiles research as fast as I can read it, gave me a tremendous assist in keeping me abreast of the current research as I wrote my book. His latest paper is entitled “How strong is the evidence that solar ultraviolet B and vitamin D reduce the risk of cancer? An examination using Hill’s criteria for causality” Although the link between vitamin D deficiency and cancer should well-established, there are those who stubbornly demand more proof while millions more die of cancer caused by vitamin D deficiency. In this paper, there is sufficient proof to convince all but the most biased reader. He uses a well-accepted scientific assessment, known as Hill’s criteria for causality, which determines whether the presence or absence of one factor causes the presence of another. In this case the “causal” factor is vitamin D deficiency, and the caused factor (result) is cancer.
Here are the qualifications for causality as established by Dr. A Bradford Hill:
1. Strength of association
2. Consistency (repeated observation)
3. Specificity (one agent, one result)
4. Temporality (exposure precedes effect)
5. Biological gradient (dose-response relation)
6. Plausibility (e.g., mechanisms)
7. Coherency (no serious conflict with the generally known facts
of the natural history and biology of the disease)
8. Experimental verification (randomized, controlled trial)
9. Analogy with other causal relationships
Using these criteria, Dr. Grant discusses the voluminous research pointing out that the vitamin D-deficiency theory of cancer causality in most deadly cancers satisfies most, if not all, of Hill’s criteria. In other words, there is little doubt that vitamin D deficiency is a primary cause of cancer. For those who are scientifically inclined, I suggest you read the paper, which you can find online by searching the citation below. If you are not so inclined, take my word for it; this paper makes an irrefutable case. Neglect your sunlight and your optimal vitamin D levels at your peril. But remember, never burn!
 Grant, W. How strong is the evidence that solar ultraviolet B and vitamin D reduce the risk of cancer? An examination using Hill’s criteria for causality Dermato-Endocrinology 2009:1:14-21.