People who binge drink on the weekend take more days off work, but the cost may be more than just economic.

Recently published research suggested alcohol and drug-related absenteeism costs the Australian economy around AU$3 billion a year. One of the report’s authors was quoted in the media as saying that “alcohol puts a bit of a tax on your immune system”. She said people may not realise drinking or drug-taking was:

causing their stomach upset, headache or worsening cold by Monday…

From the few studies that explore this, we know excess alcohol intake affects the immune system. But how does this effect manifest itself? Can a “big weekend” make people more susceptible to illness?

Heavy drinking

Complex and tightly controlled, the immune system is made up of different cells and tissues, that together protect us from viruses and bacteria.

Chronic alcohol abuse can definitely alter the way our body responds to pathogens - reducing the numbers of killer T cells, for instance. These are white blood cells that act like the immune system’s soldiers, working to eliminate infected cells.

A reduction in killer T cells leaves people more prone to infections. But it’s possible other factors sometimes present in people who chronically abuse alcohol, such as poor diet, can also have that effect.

Drinking can influence the inflammatory response too. Inflammation is an important part of the immune mechanism that helps immune cells travel to the infection site (although if uncontrolled, inflammation can cause chronic disease and pain).

One recent study found that in the 20 minutes after a binge drinking session, participants had developed higher than normal levels of inflammation in their body. But two hours later, inflammation had dropped below the original levels.

As their blood alcohol level fell, the number of monocytes (types of white blood cells known as “phagocytes” because they’re able to recognise and ingest microbes) also fell. Participants’ blood showed decreased numbers of natural killer cells as well. These play a similar role as the killer T cells.

Similar results were found in a 2014 study on binge-drinking mice; their phagocytic cells decreased along with other changes to the immune system. These findings suggest even a single session of binge drinking may increase the risk of viral infections, such as colds. But moderate drinking (one drink per day for women and two for men) shows a different picture.

Moderate drinking

A 1993 study looked at the association between smoking, drinking and the risk of developing the common cold - with volunteers given saline drops containing cold-causing viruses. It found drinking one or more glasses of alcohol a day decreased the risk. But this was only true for non-smokers; smokers were more prone to colds regardless of how much they drank.

A larger 2002 study examined the effects of wine, beer and spirits on the risk of developing the common cold. Participants were asked about their drinking and other lifestyle habits, as well as any colds they had over the course of a year.

People who drank wine - red wine in particular - had fewer colds than those who didn’t drink at all. And people who drank more than 14 glasses of wine per week had been the least ill that year. Beer and spirits didn’t appear to be protective against infection. But nor did they increase the risk of developing colds.

But these studies looked at the association between alcohol and colds. What about alcohol’s effect on the immune system itself?

The immune system

A 2014 study in which rhesus monkeys were given open access to alcohol found monkeys who consumed moderate amounts of alcohol responded better to a vaccine. And monkeys who abstained, or drank heavily, had a lower immune response.

It also found monkeys who were moderate drinkers had slightly increased levels of certain cytokines. These are small proteins that help coordinate the immune response to infections and cell damage, either enhancing or dampening the response.

In these monkeys, the number of immune response-enhancing cytokines had increased, and that might be the mechanism that helped their improved response to the vaccine. It’s possible moderate drinking in humans may also enhance the immune response to vaccines and viral infections.

Different types of alcohol, as well as different intake levels, seem to play a strong role in our susceptibility to colds. And a weekend of binge drinking may indeed increase your susceptibility to viral infections, such as colds.

Given drinking is a social activity, going out for a drink increases exposure to infections as well. Still, like many other things in life, exercising moderation when drinking could help boost your immune response to the common cold and other viral illnesses.