Two small drinks a night are enough to make elderly people unsteady on their feet putting them at risk of falls.
The moderate amount of alcohol – below the current legal limit for driving – has a dramatic effect on their dexterity.
Scientists gave 13 healthy men and women in their early sixties just two single vodka and orange drinks and found they struggled at an obstacle avoidance test while walking.
Researcher Judith Hegeman, of Saint Maartens Hospital, Nijmegen in The Netherlands, said: “The results clearly show even with low blood alcohol concentrations, reactions to sudden gait perturbations are seriously affected.
“After ingestion of two alcoholic drinks, obstacles were hit twice as often, response times were delayed and response amplitudes were reduced.
“These changes were most obvious in situations with little available response time.”
In the study published in BMC Research Notes the volunteers, whose average age was about 62, first started to walk on a treadmill at a steady walking pace.
A thin wooden block was placed at the far end of the belt and allowed to move towards the volunteer as Ms Hegeman and her colleagues measured the effects of alcohol on how capable the subjects were of stepping over the obstacle.
She said: “We found alcohol levels – considered to be safe for driving – seriously hamper the ability to successfully avoid sudden obstacles in the travel path.
“A possible limitation of this study is the relatively small sample size. However even with the small number it yielded an unequivocal outcome.”
Ms Hegeman said drinking is a well-established risk factor for traffic accidents so legal limits are set for blood alcohol concentration (BAC) and driving.
But in contrast there are no legal limits for walking even though there are numerous accounts of people stumbling and falling after consuming too much alcohol.
She said: “Alcohol, even at these low concentrations, affects brain function and increases fall risk.
“An increased fall risk has been associated with impaired obstacle avoidance skills.
“Low level BACs are likely to affect obstacle avoidance reactions during gait, since the brain areas that are presumably involved in these reactions have been shown to be influenced by alcohol.”
Ms Hegeman said this is the first study of its kind as previous research on the elderly has concentrated on the effects of alcohol on posture.
Earlier research has also shown many falls are primarily due to stumbling and tripping.
In order to avoid falls due to hitting an obstacle, one needs to be able to respond adequately to both unseen obstacles causing a stumble and to obstacles suddenly appearing in the travel path.
In general the use of alcohol is primarily seen as a risk factor for driving but one study estimated about 20% of unintentional falls at home in adults may be attributable to the consumption of two or more standard alcoholic drinks in the preceding six hours.
Ms Hegeman said: “Moreover, accidents can also occur while walking, particularly under challenging conditions such as when negotiating suddenly appearing obstacles.
“The present data show that the required skills for obstacle avoidance frequently fail even after consumption of a low dose of alcohol.”