Abstract
Our study tested the hypothesis that precipitation and climate zone play a role in determining the incidence rate of invasive cancer in the United States (Shah et al., 2019). The study included analyzing the incidence rates of total invasive cancer, breast and ovarian cancer (among females), prostate cancer (among males), lung and bronchus cancer, and colorectal cancer. The results indicated that the counties with high precipitation and cold climates have statistically significant higher incidence rates of cancer.
In the letter to the editor “The primary determinant of the geographical disparity in the invasive cancer incidence rates in the United States is solar UVB dose,” Grant (2020) claims that we have overlooked the variable of ultraviolet B (UVB) dose; he suggests that the link between UVB, vitamin D, and incidence rates of invasive cancer is conclusive in the literature. In our article, we did include the possible link between vitamin D and cancer; the link was referenced among the different mechanisms of action that were proposed for the observed correlation. However, science is far from conclusive on the link between vitamin D and cancer. In fact, in the review article authored by Grant in 2016, the conclusion on the link between UVB exposure, vitamin D intake, and cancer reads: “The evidence is not perfect, and the findings of ostensibly similar studies do not always agree” (Grant, 2016). The article further elaborates in the conclusion that health officials and medical systems will not recommend that people consume vitamin D supplements for cancer prevention until more definitive trials are conducted (Grant, 2016). The presence of a link between UVB, vitamin D, and cancer is also under debate. In a recent review, Brown (2019) suggested that low vitamin D levels could be associated with high levels of dysregulated phosphate in the body, rather than a lack of UVB exposure.
We stand by our conclusion; based on our current scientific knowledge, it is imperative for the community to consider all the possible underlying mechanisms behind the correlation between precipitation and climate zone and the incidence rates of cancer.