HONG KONG (Reuters) - A study of atomic bomb survivors in Japan conducted over 53 years has found that they appear to suffer a far higher risk of heart disease and stroke because of their exposure to radiation.

The study, published in the British Medical Journal, involved 86,611 survivors from the bombings of Hiroshima and Nagasaki in 1945, which forced Japan into surrendering to the Allied Powers and officially ending World War Two.

Each person was exposed to an absorbed radiation dose of between 0 and 4 Gy (Gray) at the time of the bombings.

Gray is the unit measuring absorbed radiation dose using special equipment called dosimeters, and the amount varies from person to person depending on their location and shielding at the time of the bombings.

This study provides the strongest evidence available to date that radiation may increase the rates of stroke and heart disease at moderate dose levels (mainly 0.5-2 Gy), though the results below 0.5 Gy are not statistically significant, said the researchers in Japan.

Further studies should provide more precise estimates of the risk at low doses, they said.

The researchers said this was an important public health issue because of the increasing use of multiple computed tomography (CT) scans and other relatively high dose diagnostic medical procedures.

Medical use of radiation is typically measured in milligray (mGy). The average radiation dose from an abdominal x-ray is 1.4 mGy (0.0014 Gy), while that from an abdominal CT scan is 8.0 mGy (0.008 Gy), and that from a pelvic CT scan is 25 mGy (0.025 Gy).

Led by Yukiko Shimizu from the Radiation Effects Research Foundation in Japan, the scientists monitored the survivors from 1950 to 2003 and found that 9,600 died from stroke while 8,400 died of heart disease.

The researchers found an elevated risk of stroke and heart disease at doses above 0.5 Gy, and chances of these conditions occurring were more likely the higher the dose.

The scientists, however, said the consequence of low radiation doses was unclear and they recommended that future research should look into this.

(Reporting by Tan Ee Lyn; Editing by Sugita Katyal)

Japan Medicine