, 6 - d ih ydro xy - 5 , 6 - d ih ydro th ym ine ) ▁is ▁one ▁of ▁the ▁principal ▁DNA ▁les ions ▁that ▁can ▁be ▁induced ▁by ▁ox id ation ▁and ▁ion izing ▁radiation . ▁ ▁A ging , ▁stroke ▁ ▁The ▁rate ▁at ▁which ▁ox id ative ▁re actions ▁generate ▁th ym ine ▁g ly col ▁and ▁th ym id ine ▁g ly col ▁in ▁the ▁DNA ▁of ▁humans ▁is ▁estimated ▁to ▁be ▁about ▁ 3 0 0 ▁per ▁cell ▁per ▁day . ▁ ▁Ox id ized ▁DNA ▁bases ▁that ▁are ▁exc ised ▁by ▁DNA ▁repair ▁processes ▁are ▁ex cret ed ▁in ▁ur ine . ▁ ▁On ▁a ▁body ▁weight ▁basis , ▁m ice ▁ex crete ▁ 1 8 ▁times ▁more ▁th ym ine ▁g ly col ▁plus ▁th ym id ine ▁g ly col ▁than ▁humans , ▁and ▁mon keys ▁four ▁times ▁more ▁than ▁humans . ▁ ▁It ▁was ▁proposed ▁that ▁rate ▁of ▁occurrence ▁of ▁ox id ative ▁DNA ▁dam ages ▁correl ates ▁with ▁met abol ic ▁rate , ▁and ▁that ▁a ▁higher ▁rate ▁of ▁ox id ative ▁damage ▁might ▁cause ▁a ▁higher ▁rate ▁of ▁cell ular ▁ag ing . ▁ ▁Base ▁exc ision ▁repair ▁is ▁a ▁major ▁DNA ▁repair ▁path way ▁for ▁removal ▁of ▁ox id ative ▁DNA ▁dam ages . ▁The ▁rate ▁of ▁repair ▁of ▁th ym ine ▁g ly col ▁damage ▁in ▁human ▁fib ro bl asts ▁was ▁found ▁to ▁decrease ▁with ▁age . ▁ ▁Bra in ▁samples ▁from ▁humans ▁who ▁died ▁of