benefits should occur for persistent oxidative damage that is related to inflammation and immune responses. some recent experiments suggest that, at least for acute high-dose irradiation, an efficient radioprotection by dietary supplements can be achieved, even in the case of exposure to high-let radiation. although there is evidence that dietary antioxidants (especially strawberries) can protect the cns from the deleterious effects of high doses of hze particles, because the mechanisms of biological effects are different at low dose-rates compared to those of acute irradiation, new studies for protracted exposures will be needed to understand the potential benefits of biological countermeasures. concern about the potential detrimental effects of antioxidants was raised by a recent meta-study of the effects of antioxidant supplements in the diet of normal subjects. the authors of this study did not find statistically significant evidence that antioxidant supplements have beneficial effects on mortality. on the contrary, they concluded that β-carotene, vitamin a, and vitamin e seem to increase the risk of death. concerns are that the antioxidants may allow rescue of cells that still sustain dna mutations or altered genomic methylation patterns following radiation damage to dna, which can result in genomic instability. an approach to target damaged cells for apoptosis may be advantageous for chronic exposures to gcr. individual risk factors individual factors of potential importance are genetic factors, prior radiation exposure, and previous head injury, such as concussion. apolipoprotein e (apoe) has been shown to be an important and common factor in cns responses. apoe controls the redistribution of lipids among cells and is expressed at high levels in the brain. new studies are considering the effects of space radiation for the major isoforms of apoe, which are encoded by distinct alleles (ε2, ε3, and ε4). the isoform apoe ε4 has been shown to increase the risk of cognitive impairments and to lower the age for alzheimer's disease. it is not known whether the interaction of radiation sensitivity or other individual risks factors is the same for high- and low-let radiation. other isoforms of apoe confer a higher risk for other diseases. people who carry at least one copy of the apoe ε4 allele are at increased risk for atherosclerosis, which is also suspected to be a risk increased by radiation. people who carry two copies of the apoe ε2 allele are at risk for a condition that is known as hyperlipoproteinemia type iii. it will therefore be extremely challenging to consider genetic factors in a multipleradiation-risk paradigm. conclusion reliable projections for cns risks from space radiation exposure cannot be made at this time due to a paucity of data on the subject. existing animal and cellular data do suggest that space radiation can produce neurological and behavioral effects; therefore, it is possible that mission operations will be impacted. the significance of these results on the morbidity to astronauts has not been elucidated, however. it is to be noted that studies, to date, have been carried out with relatively small numbers of animals (<10 per dose group); this means that testing of dose threshold effects at lower doses (<0.5 gy) has not yet been carried out to a sufficient extent. as the problem of extrapolating space radiation effects in animals to humans will be a challenge for space radiation research, such research could become limited by the population size that is typically used in animal studies. furthermore, the role of dose protraction has not been studied to date. an approach has not been discovered to extrapolate existing observations to possible cognitive changes, performance degradation, or late cns effects in astronauts. research on new approaches to risk assessment may be needed to provide the data and knowledge that will be necessary to develop risk projection models of the cns from space radiation. a vigorous research program, which will be required to solve these problems, must rely on new approaches to risk assessment and countermeasure validation because of the absence of useful human radio-epidemiology data in this area.