It seems to depend on the way the observational, epidemiological and correlational data is used. That is: how the data is gathered, analysed and interpreted. And how puritan the belief systems of the researchers are.
Drinking large amounts of alcohol is bad. Doing that daily is bad.
A recent study amassed a huge dataset and concluded that the only safe amount of alcohol is zero. This got even published ion The Lancet as
"Alcohol use and burden for 195 countries and territories, 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016"
The key findings are communicated in the extreme, globally, and badly:
Analysing data from 15 to 95-year-olds, the researchers compared people who did not drink at all with those who had one alcoholic drink a day.
They found that out of 100,000 non-drinkers, 914 would develop an alcohol-related health problem such as cancer or suffer an injury.
But an extra four people would be affected if they drank one alcoholic drink a day.
For people who had two alcoholic drinks a day, 63 more developed a condition within a year and for those who consumed five drinks every day, there was an increase of 338 people, who developed a health problem.
That is from a baseline of 914 problems in 100000 people an increase to 918 people in 100000 for one drink a day. As one can see, problems usually related to alcohol develop in 914 non-drinkers already or as well and one drink a day means trouble for an additional 4 people.
Is much or not? If that is difficult to picture mentally, The Lancet provides you the service of a picture that gets overlooked in the sensationalist press:
The relative risk increase in a study that claims zero is the only safe level for one drink per day is effectively zero as well.
This study aims at scare mongering and has to admit that
Alcohol use is a leading risk factor for death and disability, but its overall association with health remains complex given the possible protective effects of moderate alcohol consumption on some conditions.
This study still does not challenge "moderate alcohol consumption may be preventive for some conditions such as ischaemic heart disease and diabetes" but looks at the effects associated with each individual health outcome together with level of alcohol consumption. When those inferences are then combined into an aggregate according to the author's model we arrive at the picture above.
Specifically, comparing no drinks with one drink a day the risk of developing one of the 23 alcohol-related health problems was 0.5% higher — meaning 914 in 100,000 15–95 year olds would develop a condition in one year if they did not drink, but 918 people in 100,000 who drank one alcoholic drink a day would develop an alcohol-related health problem in a year.
This increased to 7% in people who drank two drinks a day (for one year, 977 people in 100,000 who drank two alcoholic drinks a day would develop an alcohol-related health problem) and 37% in people who drank five drinks every day (for one year, 1252 people in 100,000 who drank five alcoholic drinks a day would develop an alcohol-related health problem).
How do experts judge this data?
David Spiegelhalter, Winton Professor for the Public Understanding of Risk at the University of Cambridge, said:
“According to data provided by the authors but not published in the paper, to suffer one extra alcohol-related health problem, around 1,600 people would need to drink two drinks totalling 20g (2.5 units) of alcohol a day for a year. This is equivalent to around 32 standard 70cl bottles of gin over a year, so a total of 50,000 bottles of gin among these 1,600 people is associated with one extra health problem. This indicates a very low level of harm in moderate drinkers, and suggests UK guidelines of an average of 16g a day (2 units) are very low-risk indeed.
“Given the pleasure presumably associated with moderate drinking, claiming there is no ‘safe’ level does not seem an argument for abstention. There is no safe level of driving, but government do not recommend that people avoid driving. Come to think of it, there is no safe level of living, but nobody would recommend abstention.”
This same year another Lancet paper tried to tackle the problem:
Angela M Wood et al.: "Risk thresholds for alcohol consumption: combined analysis of individual-participant data for 599 912 current drinkers in 83 prospective studies", Volume 391, Issue 10129, p1513-1523, April 14, 2018
Low-risk limits recommended for alcohol consumption vary substantially across different national guidelines. To define thresholds associated with lowest risk for all-cause mortality and cardiovascular disease, we studied individual-participant data from 599 912 current drinkers without previous cardiovascular disease.
In current drinkers of alcohol in high-income countries, the threshold for lowest risk of all-cause mortality was about 100 g/week. For cardiovascular disease subtypes other than myocardial infarction, there were no clear risk thresholds below which lower alcohol consumption stopped being associated with lower disease risk. These data support limits for alcohol consumption that are lower than those recommended in most current guidelines.
Again, a call "to lower guidelines". Despite the result that for some outcomes the lowest risk was not "zero drinks" but that the relative risk increases, clearly, if you go below 100g of pure alcohol a week!
From the supplementary material: (click to enlarge)
Do these numbers really suggest that not drinking alcohol – either never or even worse to quit drining – is to be seen as a potential risk factor? The huge difference between never-drinkers and ex-drinkers might spoil that party a bit. An equally plausible explanation for that is that dislike for alcohol might be a sign for already frail or future health problems.
The vast majority of findings show that moderate drinking (definitions of that may vary as much as does individual tolerance) carries a low risk and that there is an ultimately unexplained correlation between drinking a bit and slightly longer life expectancy. The French Paradox keeps on giving.