Damage to the DNA of germ cells can lead to mutation, which may result in birth defects, genetic diseases, and cancer. The very high endogenous rate of oxidative DNA damage and the importance of dietary ascorbic acid (AA) in preventing this damage has prompted an examination of these factors in human sperm DNA. The oxidized nucleoside 8-hydroxy-2'-deoxyguanosine (8-oxo-7,8-dihydro-2'-deoxyguanosine; oxo8dG), 1 of approximately 20 major products of oxidative damage to DNA, was measured in DNA isolated from human sperm provided by healthy subjects and compared to the seminal fluid AA levels. This relationship was studied in two groups. In a group of 24 free-living individuals 20-50 years old high levels of oxo8dG were correlated with low seminal plasma AA. The endogenous level of oxo8dG in this group was 13 fmol per microgram of DNA or approximately 25,000 adducts per sperm cell. The second group of individuals was maintained on a controlled diet that varied only in AA content. When dietary AA was decreased from 250 to 5 mg/day, the seminal fluid AA decreased by half and the level of oxo8dG in sperm DNA increased 91%. Repletion of dietary AA for 28 days (from 5 mg/day to 250 or 60 mg/day) caused a doubling in seminal fluid AA and reduced oxo8dG by 36%. These results indicate that dietary AA protects human sperm from endogenous oxidative DNA damage that could affect sperm quality and increase risk of genetic defects, particularly in populations with low AA such as smokers.
