Abstract
There are 52,380 cases of leukemia and 24,090 deaths from it in the US annually. Its causes are unknown and no preventive strategies have been implemented. We hypothesized that leukemia is due mainly to vitamin D deficiency, which is due mainly to low solar ultraviolet B (UVB) irradiance. To test this hypothesis, we estimated age-standardized cloud-cover-adjusted winter UVB irradiance using cloud cover data from the International Satellite Cloud Climatology Project, latitudes of population centroids, and standard astronomical calculations. Incidence rates for 172 countries, available from the International Agency for Cancer Research, were plotted according to cloud-adjusted UVB irradiance. We used multiple regression to account for national differences in elevation and average life expectancy. Leukemia incidence rates were inversely associated with cloud-adjusted UVB irradiance in males (p ≤ 0.01) and females (p ≤ 0.01) in both hemispheres. There were few departures from the trend line, which was parabolic when plotted with the equator at the center of the display, northern hemisphere countries on the right side and southern hemisphere countries on the left. The bivariate association displayed by the polynomial trend line indicated that populations at higher latitudes had at least two times the risk of leukemia compared to equatorial populations. The association persisted in males (p ≤ 0.05) and females (p ≤ 0.01) after controlling for elevation and life expectancy. Incidence rates of leukemia were inversely associated with solar UVB irradiance. It is plausible that the association is due to vitamin D deficiency. This would be consistent with laboratory studies and a previous epidemiological study. Consideration should be given to prudent use of vitamin D for prevention of leukemia.
Highlights
It was estimated that the United States had 52,380 new cases and 24,090 deaths from leukemia in 2014 [1]
Cloud cover-adjusted ultraviolet B (UVB) was estimated for each country from cloud cover data, available from the National Aeronautics and Space Administration’s (NASA) International Satellite Cloud Climatology Project (ISCCP) satellite [16], and from total noon solar irradiance at the winter solstice at the latitude of the population centroid of each country
Leukemia incidence rates for 172 countries were inversely associated with cloud-adjusted UVB irradiance in males (p < 0.01) and females (p < 0.01) in both hemispheres (Fig 1, Fig 2)
Summary
It was estimated that the United States had 52,380 new cases and 24,090 deaths from leukemia in 2014 [1]. Numerous laboratory studies have been conducted on the HL60 line of AML cells [3,4,5,6]. These studies have supported a biological mechanism of action whereby leukemia cells are acted upon by vitamin D metabolites. A separate study found that supplementation with 1,25-dihydroxyvitamin D increased survival time in mice with myeloid leukemia [4]. A clinical study found that lower 25-hydroxyvitamin D levels was associated with poorer relapse-free survival, a finding that persisted even after controlling for smoking and white blood cell count [7]. A case-control study found that all patients with acute leukemia had 25-hydroxyvitamin D levels below 20 ng/ml [8]
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