Wine glass size may be key to how much you drink: Study

The size of glass used for serving wine can influence the amount of wine you drink in restaurants, according to a Cambridge study.

The study, published in the journal Addiction, found that when restaurants served wine in 370 millilitre (ml) rather than 300ml glasses they sold more wine, and tended to sell less when they used 250ml glasses.

The researchers from the University of Cambridge in the UK did not see such effects in bars.

Alcohol is the fifth largest contributor to early death in high-income countries and the seventh worldwide, they said.

One proposed way of reducing the amount of alcohol consumed is to reduce the size of wine glasses, they said.

Until now the evidence supporting such a move has been inconclusive and often contradictory, the researchers said.

Wine glasses have increased in size almost seven-fold over the last 300 years with the most marked increase being a doubling in size since 1990, they said.

Wine sales in bars and restaurants are either of fixed serving sizes when sold by the glass, or sold by the bottle for free-pouring by customers or staff, particularly in restaurants.

The latest study suggests that serving wine in larger wine glasses -- while keeping the measure the same -- led to a significant increase in the amount of wine sold.

To provide a robust estimate of the effect size of wine glass size on sales -- a proxy for consumption -- the team did a 'mega-analysis'.

The researchers brought together all of their previously published datasets from studies carried out between 2015 and 2018 at bars and restaurants in Cambridge.

In restaurants, when glass size was increased to 370ml, wine sales increased by 7.3 per cent, they found.

Reducing the glass size to 250ml led to a drop of 9.6 per cent, according to the study.

However, increasing the glass size further to 450ml made no difference compared to using 300ml glasses.

"Pouring wine from a bottle or a carafe, as happens for most wine sold in restaurants, allows people to pour more than a standard serving size, and this effect may increase with the size of the glass and the bottle," explained the first author of the study Mark Pilling.

"If these larger portions are still perceived to be 'a glass', then we would expect people to buy and consume more wine with larger glasses," Pilling said.

The researchers noted that as glass sizes of 300ml and 350ml are commonly used in restaurants and bars, drinkers may not have noticed the difference, and still assumed they were pouring a standard serving.

When smaller glass sizes of 250ml are available, they may also appear similar to 300ml glasses but result in a smaller amount of wine being poured, according to the researchers.

"In contrast, very large glasses, such as the 450ml glasses, are more obviously larger, so drinkers may have taken conscious measures to reduce how much they drink, such as drinking more slowly or pouring with greater caution," Pilling added.

The researchers also found similar internal patterns to those reported in previous studies, namely lower sales of wine on warmer days and much higher sales on Fridays and Saturdays than on Mondays.

They noted that there was no significant differences in wine sales by glass size in bars -- in contrast to the team's earlier study.