LeukemiaExposure to sunlight

Inspection of the geographical variation of leukemia mortality rate in the United States1 indicates that the pattern found for most vitamin D-sensitive cancers, highest rates in the northeast, lowest in the southwest, is not the pattern for leukemia. Instead, the highest mortality rates are in the middle third going from east to west. However, the lowest rates are in the southwest. The likely reason for this pattern is the effect of agricultural pesticides on risk of leukemia2 3 4.

One paper reported a decrease of leukemia mortality rate with increasing altitude of residence for altitudes above 2000 feet:

From published demographic data and leukemia mortality data, the leukemia mortality rate per 100,000 population/yr was correlated with altitude. The findings of this study indicate that the leukemia mortality rate increases with increasing altitude up to about 2000 ft elevation, but that above 2000 ft the leukemia mortality rate decreases significantly with increasing altitude5.

However, looking at the Atlas of Cancer Mortality in the United States1, this could be an effect related to pesticide use in lower-altitude regions rather than a beneficial effect of solar UVB irradiance.

Childhood Acute lymphoblastic leukemia (ALL) was found to have an excess rate of about 50% for those born in winter/spring compared to summer/fall in Denmark6. It was suggested that the reason for seasonality could be maternal infection during pregnancy, giving the developing fetus exposure to the infection agent. Influenza infection rates are highest in winter due, in part, to lower solar UVB doses in winter7 8.

Acute leukemia (AL), especially Acute myelogenous leukemia (AML), seems to have highest risk in winter, suggesting that low serum 25(OH)D levels in winter are associated with increased risk9 10.

Month of diagnosis of 7,423 cases of AL in Finland during 1964-2003 were linked with data on influenza and solar radiation. AML showed the highest risk in the dark season. During the light season, the incidence decreased by 58% (95% confidence interval, 16-79%) per 1,000 kJ/m(2)/d increase of solar radiation. Independent of solar radiation, AML increased by 9% (95% confidence interval, 0-19%) during influenza epidemics. Reoccurring at the same time annually, darkness-related vitamin D deficiency and influenza could cause successive and co-operative mutations leading to AL with a short latency 10.

Childhood leukemia has been linked to infections in winter in the UK11.

There is some evidence of higher risk for ALL in northern Europe but not elsewhere12 13.

A study in the United Arab Emirates (UAE) found a higher rate of acute lymphoblastic leukemia (ALL) among native females than native males, which is the opposite of what is found in other countries, suggesting that low serum 25(OH)D levels among females due to covering more of the skin while in the sun14.

An ecological study in China found an inverse correlation between annual solar UVB doses and leukemia incidence and mortality rates in rural regions, but an increased risk in urban regions15. Those living in rural regions are much more likely to spend significant time out of doors, possibly by working in agriculture.Thus this study provides evidence of a beneficial effect of UVB irradiance in reducing the risk of leukemia.

Based on the totality of the evidence, there is modest evidence that higher solar UVB doses are associated with lower risk of leukemia.

Page last edited: 22 August 2011


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  2. Beane Freeman, L. E. Bonner, M. R. Blair, A. Hoppin, J. A. Sandler, D. P. Lubin, J. H. Dosemeci, M. Lynch, C. F. Knott, C. Alavanja, M. C. Cancer incidence among male pesticide applicators in the Agricultural Health Study cohort exposed to diazinon. Am J Epidemiol. 2005 Dec 1; 162 (11): 1070-9.
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