A magnitude nine earthquake and tsunami in 2011 devastated the Fukushima Daiichi nuclear plant
"A breakdown of data, based on age, gender and proximity to the plant, does show a higher cancer risk for those located in the most contaminated parts," Dr Maria Neira, the organisation's director for public health and environment, said in a statement on Tuesday.
A magnitude nine earthquake and tsunami on March 11 2011 killed nearly 19 000 people and devastated the Fukushima Daiichi nuclear plant, triggering meltdowns, spewing radiation and forcing about 160 000 people to flee their homes.
It was the worst nuclear accident since a reactor exploded at the Chernobyl power plant in Ukraine in 1986.
In the most contaminated area, the World Health Organisation estimated that there was a 70% higher risk of females exposed as infants developing thyroid cancer over their lifetime. The thyroid is the most exposed organ as radioactive iodine concentrates there and children are deemed especially vulnerable.
The report estimated that in the most contaminated area there was a 7% higher risk of leukaemia in males exposed as infants, and a 6% higher risk of breast cancer in females exposed as infants.
The report concluded that for the general population inside Japan, the predicted health risks were low but that one-third of emergency workers were estimated to have increased risk.
Radiation doses
But there was no discernible increase in health risks expected outside Japan, the organisation said in a 200-page report which was based on a comprehensive assessment by international experts.
Jim Smith, professor of environmental science at the University of Portsmouth in England, said: "Apart from emergency workers, the most affected people were those who remained in some highly contaminated towns and villages to the north-west of the power station for up to four months before evacuation.
"The report found that these people received a lifetime radiation dose of up to 50 milli-Sieverts and therefore have a significant, but relatively small, additional risk of contracting cancer in later life."
Smith said the average British person receives more than 150 milli-Sieverts during their lifetime from background radiation.
He said the report did not yet give data on the numbers of people who received particular radiation doses, so it was not yet possible to estimate the overall health consequences.
Neira said: "The World Health Organisation report underlines the need for long-term health monitoring of those who are at high risk, along with the provision of necessary medical follow-up and support services."
Fukushima operator Tokyo Electric Power Company earlier this month received approval to tap the Japanese government for 697-billion yen to compensate those harmed by the disaster, taking the total fund to 3.24-trillion yen. – Reuters