Ascorbic acid gives different protective effects in human cells exposed to X-rays and heavy ions.

We studied the effects and mechanisms of ascorbic acid as a radiation protector. Cell survival, repair of DNA double strand breaks (DSBs), and sister chromatid exchanges (SCEs) were examined in normal human fibroblasts irradiated with X-rays and heavy ions. Post-irradiation treatment with 5mM ascorbic acid for 24 h in plateau phase (non-cycling) cells enhanced cell survival and DNA double strand break repair, and reduced SCEs after X-rays irradiation. On the other hand, only reduced SCEs were observed after heavy ion exposure such as to carbon ions. Judging from our data, it is possible that the radioprotective action of ascorbic acid would be effective in non-complex type DNA damage such as induced by X-rays. These findings provide new insight into the mechanism of DNA damage and repair produced by heavy ion irradiation.