Covid 19 coronavirus: Does alcohol weaken the immune system?

Are you worried that your alcohol consumption is creeping up during the coronavirus lockdown?

Well, you're not alone.

We may not be drinking to excess, but with everyone stuck at home, it seems the lure of a cheeky glass of wine or beer is hitting many of us earlier – and harder – each day than normal.

At what price? Of course, we've all heard the usual (scientifically backed) stories about the damage booze does but a new worry is circling among the nation's wine-o-clockers: does alcohol weaken the immune system?

The question is a rising search term on Google at the moment, and you can see why: during the coronavirus pandemic, we want our immune systems to be in tip-top conditions. So, what does science say about the effect of booze on our systems?

To answer that question, the starting point is to say that we know that long-term alcohol misuse damages the immune system. Post-mortem studies of chronic drinkers have found that they tend to have fewer immune cells in their blood than non-drinkers.

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There are several mechanisms by which alcohol misuse can damage the immune system in several ways. It can relax the gut barrier, allowing more bacteria to pass into the blood. This depletes immune cells including macrophages, T and C cells, which work together to identify and destroy pathogens in your system. With fewer macrophages in the blood, the immune response is less pronounced.

Alcohol can also affect the upper respiratory system, impairing the function of immune cells in the lungs. This can often remain undetected until a more serious respiratory problem occurs. Then, frequent drinkers get it worse than those who don't drink.

A 2004 study also found that extensive drinking reduced the function of monocytes. These are the white blood cells on the front-line of immune defence, which detect viruses and bacteria and then produce a chemical called type-1 interferon to summon other immune cells to fight the infection. The study found that monocytes exposed to the level of blood alcohol that results from drinking four or five drinks a day for a week only produced a quarter of the chemical as those which were not exposed to alcohol.

Which all suggests you shouldn't be drinking extensively during coronavirus (nor should you be drinking heavily after the pandemic has subsided, either, for that matter).

However, the landscape changes slightly when you look at moderate levels of drinking. Indeed, some studies have even suggested that moderate alcohol consumption is good for us.

A 2016 study trained monkeys to consume alcohol in water. One group drank a lot of the alcoholic water, one group drank less, one group drank none at all. The immune response in the group who drank a lot of alcohol was the worst, followed by the teetotal group. The best immune response was recorded in the moderate-drinking monkeys.

A scientific literature review from the University of Cambridge noted "moderate alcohol consumption (up to three to four drinks per day) has been associated with either no risk or a decreased risk for upper respiratory infections". (We should add here that three or four drinks a day puts you well over the government's alcohol consumption guideline and leaves you at increased risk of a slew of diseases, from cancer to heart disease.)

The Cambridge review suggested that moderate alcohol consumption might help the immune system because of the same anti-inflammatory effects that we often hear about associated with red wine.

Inflammation is part of the body's immune response. The body releases cytokines to cause inflammation to help isolate the infected part of the body. The trouble is that too many cytokines can damage healthy cells. Alcohol is known to disrupt the release of cytokines, which may help regulate the levels of inflammation. Therefore, too much alcohol prevents inflammation, harming immune response. However, a moderate amount may help prevent over-inflammation.

It remains up for debate as to whether it is the ethanol content of alcohol or some other part of a drink's chemical make-up that produces its anti-inflammatory effects. Some studies have looked into whether the type of alcohol makes a difference. One found that wine is more likely to have an anti-inflammatory effect than gin, for example.

Ultimately, the Cambridge review of the evidence concludes there "is enough evidence to suggest that there are some compounds in polyphenolic-rich alcoholic beverages such as wine or beer that prevent suppression of the immune system or could trigger a protective effect." But before you pour yourself a big glass of wine, it's worth noting, the review continues, "although the moderate consumption of beer or wine seem to exert some benefits on the immune response in healthy adults, given the serious health risks associated with exceeding two drinks per day, increased alcohol consumption cannot be recommended".

In summary then: excessive alcohol is bad for your immune system; moderate drinking could be good for it, but either way you probably shouldn't be drinking more than usual.

• Covid19.govt.nz: The Government's official Covid-19 advisory website