Low sunlight exposure increases cancer risk

Analysing data on leukemia incidence rates in 172 countries, the researchers found that people living in higher latitudes are at least two times at greater risk of developing leukemia than equatorial populations.

"These results suggest that much of the burden of leukemia worldwide is due to the epidemic of vitamin D deficiency we are experiencing in winter in populations distant from the equator," said Cedric Garland, adjunct professor at University of California, San Diego School of Medicine in the US.

Leukemia rates were highest in countries relatively closer to the poles, such as Australia, New Zealand, Chile, Ireland, Canada and the United States. 

They were lowest in countries closer to the equator, such as Bolivia, Samoa, Madagascar and Nigeria, the findings showed.

"People who live in areas with low solar ultraviolet B (UVB) exposure tend to have low levels of vitamin D metabolites in their blood," Garland said. 

"These low levels place them at high risk of certain cancers, including leukemia," Garland noted.

Vitamin D abundantly produced when ultraviolet radiation from sunlight strikes the skin and triggers synthesis. 

The researchers analysed age-adjusted incidence rates of leukemia in 172 countries from GLOBOCAN, an international agency for research on cancer that is part of the World Health Organization.

They comparing that information with cloud cover data from the International Satellite Cloud Climatology Project. 

The researchers found that reduced UVB radiation exposure and lower vitamin D levels were associated with higher risks of cancer.

The findings were published online in the journal PLOS One.