People's estimates of how much they drink are much higher when they include weekends and holidays, according to a new survey from the UK.
In England, surveys measuring everyday alcohol consumption account for only 60 per cent of the total alcohol sold in stores, the researchers write in BMC Medicine.
By only focusing on typical drinking patterns, surveys miss a lot of alcohol consumption that happens on special occasions like weddings, holidays, and sporting events, according to Mark Bellis, the lead author on the study.
"We wanted to better understand drinking patterns to better inform people about the risks and improve public health responses to drinking," said Bellis, the director of policy, research and development for Public Health Wales.
The researchers conducted a phone survey of over 6,000 people over the age of 16 in England to assess the amount of special occasion drinking that may not be picked up by other surveys.
Respondents were asked about their alcohol consumption on days where they drank more than usual. This included less typical days such as Friday nights, as well as their average number of drinks during holidays and events.
Overall, 4,604 of the survey subjects said they were "current drinkers."
Responses from these individuals showed that on atypical and special occasions, people drank an extra 120 million units of alcohol per week in England, or the equivalent of 12 million bottles of wine.
The researchers defined one unit of alcohol as 8 grams of pure alcohol, while the Centres for Disease Control and Prevention defined a standard drink as having 14 grams.
The greatest increase in drinking was among the 25-34 year-olds who had the highest everyday drinking rates. For this group, special occasion drinking added 18 units per week for both men and women.
Overall, when including atypical drinking, 25- to 34-year-old men reported the highest weekly consumption of alcohol.
In general, men added a higher number of drinks on special occasions, but women had the greatest increases relative to how much they generally drank.
People who reported lower rates of drinking, one unit or less per week, showed a large increase and drank more than twice as much over special occasions.
According to the authors, adding in the extra atypical and special occasion drinking accounts for more than 40 per cent of the gap between previous surveys of alcohol consumption and actual alcohol sales in England.
"Most people underestimate their atypical consumption. They also underestimate the risk for harm associated with their drinking. Many people unknowingly seem to accept much higher risks from alcohol consumption compared to other risks," said Michael Roerecke, an independent scientist at the Center for Addiction and Mental Health in Canada.
According to the World Health Organisation, alcohol is related to more than 200 health conditions and causes nearly 6 per cent of all deaths globally.
Roerecke, who was not involved in the study, said in an email that the health risks of drinking heavily over time can include high blood pressure, liver disease, and many types of cancer.
Roerecke also noted that heavy drinking on special occasions can also put people at risk for injury, even if this behaviour is rare.
Bellis agreed, saying in an email that when people consume a large number of drinks in one sitting, they "increase their risks of being involved in accidents, violence and overdose."
Bellis advises, "Think about how much you consume, especially on those nights and times of the year when you might be drinking more."