Commentary: time for public health action on vitamin D for cancer risk reduction.

The seminal paper by Garland and Garland 1 continues the tradition of observation and inference leading the way to discovery of new methods for preventing or curing disease. Their paper broke ground by marshalling the evidence for the vitamin D-cancer hypothesis. Their work directly confronted the prevailing paradigms that the main risk factors for colon cancer were deficient fibre intake, excessive fat intake, and/or genetic predisposition. At that time it was hard to envision that a geophysical characteristic, such as solar ultraviolet-B (UVB) radiation, through photosynthesis of vitamin D, would reduce cancer risk. Solar UVB was considered mainly harmful, and the findings of the paper did not support the paradigms. In some ways it was not surprising that their hypothesis opposed the conventional wisdom. Many diseases have been eliminated by the epidemiological approach when other approaches have not been successful. In 1645 a slum-dwelling toddler was taken to a clinic for the poor because he could not walk, his legs being bizarrely weak and twisted. Within a few decades, the feared disease that came to be known as rickets was present in a majority of London children. Early death was common. As with pellagra, the tendency of the disease to run in families led many to regard it as hereditary. Despite 335 years of recognition of the disease, there had been neither cure nor means of prevention. But when incidence rates worldwide were plotted on a map in 1890, an inverse association was noted with sunlight. Children were soon placed in sunlight or briefly exposed to an artificial source of UVB, and the disease was either prevented or cured in the young. It took almost 100 years from the discovery that UVB and vitamin D prevented rickets to the realization that they reduced the risk of colon, 1 breast, 2 and ovarian 3 cancers. With unusual speed in biomedical history, a risk-reducing role of UVB and vitamin D was found for prostate, 4 bladder, oesophageal, gastric, pancreatic, rectal, renal, and corpus uteri cancer, and nonHodgkin’s lymphoma. 5 The total number of vitamin D-sensitive cancers determined to date is at least 18. 1–7