Research decodes why heavy drinkers are prone to accidents

Heavy drinkers who believe that they can 'handle their alcohol' may be prone to more accidents or injuries while intoxicated, as they can not correctly judge if they can safely attempt difficult tasks.

Heavy drinkers develop behavioral tolerance to alcohol over time on some fine motor tasks, but not on more complex tasks.

While heavy drinkers showed less impairment than light drinkers on a rote fine motor test over time, they did not perform better on a test involving more short-term memory, motor speed, and more complex cognitive processing.

Researchers from Veterans Affairs San Diego Healthcare System in the US, tested about 155 young adult volunteers on two cognitive and motor coordination tests at the beginning of the study and again five years later.

They defined a heavy drinker as a person who drank between 10 and 40 alcoholic drinks per week for at least the past two years at the initial testing.

Light drinkers were those who had fewer than six drinks per week. Participants maintained these drinking habits across the five years between initial testing and follow-up.

Participants completed two psychomotor tasks. They were timed moving, inserting, and rotating pegs into slotted holes on a board. This test measures fine motor skills.

Participants were then given a legend with different symbols corresponding to numbers. They then had 90 seconds to fill in the correct symbols on a sheet with numbers.

Before each test, participants were given a dose of alcohol that was calculated based on their body weight to bring them to a specific breath alcohol concentration.

They were then tested at 30, 60, 120, and 180 minutes after the drink.

Researchers found that participants performed worse on both tests when impaired by alcohol.

At the 5-year follow-up, both groups showed improvement on both tasks compared with how they had done earlier.

Heavy drinkers also showed evidence of chemical tolerance to alcohol. Their breath alcohol concentrations decreased faster after drinking at the five-year retest versus the initial test, researchers said.

While both groups did better at the follow-up, heavy drinkers showed less impairment on the pegboard than light drinkers relative to their initial testing scores.

All in all, the results show that sustained heavier drinking may lead to less impairment in simpler fine motor skills relative to lighter drinking.

However, this tolerance does not help performance on tasks involving more complex motor processing and short-term memory, researchers said.

"Overall, there is a common belief among heavy drinkers that they can 'handle their alcohol' and that many common daily tasks may not be affected by their alcohol use," said Ty Brumback from Veterans Affairs San Diego Healthcare System.

"The take-home message here is that tolerance to alcohol is not equal across all tasks and is not 'protective' against accidents or injuries while intoxicated, because it may in fact lead the heavy drinker to judge that they are not impaired and attempt more difficult tasks," Brumback said.

The study was publishe in the journal Psychopharmacology.