Differences in psychomotor reaction time in male monozygotic twins discordant for lifetime cigarette smoking.

The effects of long-term cigarette smoking on psychomotor reaction time were investigated among 8 pairs of monozygotic male twins highly discordant for lifetime smoking (means 32.4 versus 0.6 pack-years). The men had no diagnosed cardiovascular disease or other major diseases, musculoskeletal complaints, or vision problems that might interfere with reaction time testing. The twins had similar education, work, and exercise histories; alcohol and coffee consumption and exposure to solvents were examined as possible confounds. Direct comparison of cotwins also controlled for age, genetics, and possible early environmental factors. Simple and choice reaction time were measured in the dominant hand and in both feet. The decision-time component of total reaction time was of primary interest. On average, long-term smokers had slower decision times than their nonsmoking twins; however, the differences were small (5 to 14%) and were not statistically significant for four of the six decision-time measures, perhaps due to the lack of power with only eight twin pairs. Further study may confirm our evidence suggesting that long-term cigarette smoking impedes reaction time, a key measure of function of the central nervous system.