SLEEPING for two hours extra a night can reduce sensitivity to pain and can be more effective than strong painkillers, according to a new study.  Scientists say ten hours of sleep a night – rather than the recommended eight – is more effective in reducing pain than codeine. Researchers studied 18 volunteers over four nights and found that those who slept for 10 hours were able to keep their finger on a heat source for 25 seconds longer than those who had eight hours or fewer.  The findings, published in the journal Sleep, also revealed the effect was greater than was seen in a previous study where volunteers were given 60mg of the painkiller codeine. The results, combined with data from previous research, suggest increased pain sensitivity in tired people is the result of their underlying sleepiness.