Countries far from equator at higher risk of leukaemia due to lower sunlight exposure, vitamin D deficiency

People living in countries closer to the poles, including Australia and New Zealand, are at higher risk of developing leukaemia, a new study warns. Higher latitude areas were found to have at least two times greater risk for leukaemia than those near the equator due to lower exposure to sunlight or ultraviolet B (UVB) and vitamin D deficiency.

Epidemiologists at University of California, San Diego said low solar ultraviolet B exposure could lead to low levels of vitamin D metabolites in the blood, which may contribute to development of certain cancers, including leukaemia.

The study, published in the journal PLOS ONE, highlights ultraviolet radiation from sunlight can produce more abundant amount of vitamin D than foods when it strikes the skin and triggers synthesis. It warns that places experiencing winter are at risk of an “epidemic of vitamin D deficiency.”

Aside from Australia and New Zealand, highest rates of leukaemia cases were found in other countries far from the equator and closer to the poles, such as Chile, Ireland, Canada and the United States. Leukaemia rates were lowest in countries near the equator, such as Bolivia, Samoa, Madagascar and Nigeria.

"These results suggest that much of the burden of leukaemia worldwide is due to the epidemic of vitamin D deficiency we are experiencing in winter in populations distant from the equator," said Cedric Garland, a professor in the Department of Family Medicine and Public Health and member of Moores Cancer Centre at UC San Diego Health.

The findings come from the analysis of age-adjusted incidence rates of leukaemia in 172 countries from GLOBOCAN, an international agency focused on cancer research and a part of the World Health Organisation. The study also backs findings of previous studies by the same research team about cancers, including breast, colon, pancreas, bladder and multiple myeloma.

Each study shows low exposure to solar ultraviolet B radiation and lower vitamin D levels were linked with higher risks of cancers. "These studies do not necessarily provide final evidence, but they have been helpful in the past in identifying associations that have helped minimize cancer risk," Garland said.