Fancy that - drug addicts have worse health than the general population

It's quite amazing what modern science can tell us these days. The Lancet has just surprised with the news that drug addicts have worse general health outcomes than society in general:

Britain’s most socially excluded groups are 10 times more likely to die early than the general population, according to analysis showing inequality is more pronounced than is documented. Its lead author said the disparity exposed “something toxic in our society”.

The findings, published in the Lancet and described as the most comprehensive assessment conducted into levels of mortality inequality, reveal women in socially excluded groups are 12 times more likely to die than other women of the same age, while men are eight times more likely.

Well, that's how it is being presented. That this is all about inequality, social exclusion and if we just equalised cash incomes some (or perhaps a lot) more then such social evils would disappear. Except this is to make the Michael Marmot mistake, to note economic inequality and some set of ills and assume that it's the inequality causing said ills.

The actual paper tells us a little more:

 Inclusion health focuses on people in extremely poor health due to poverty, marginalisation, and multimorbidity. We aimed to review morbidity and mortality data on four overlapping populations who experience considerable social exclusion: homeless populations, individuals with substance use disorders, sex workers, and imprisoned individuals.

Mortality here is when people die, morbidity is why. That proper definition of homelessness, rough sleeping, finds that near all are either highly transient or suffering from one or more substance disorders or mental health problems. The low end of prostitution is rather well known for being engaged in to feed a drug habit. The prisons are full of those there for (and still engaging in) drug habits. We're not really studying four discrete populations here at all.

But leave that aside and think of what they're really saying. Those who inject anything from brick dust through rat poison to synthetic opioids along with their heroin have worse health outcomes than the general population? Sex work is a dangerous occupation? OK, we'll accept those contentions.  But this is caused by economic inequality, social exclusion? Rather, than, perhaps the injection of rat poison mixed with brick dust? 

Note also that very economic inequality being complained of. At least two of our four groups are poor because of their behaviour - both prison and junkies' wages are notoriously low. That is, both the ill health and the inequality are being caused by the activities, not inequality itself producing either the actions nor the health outcomes.

But then this is modern science of a kind, isn't it? Deliberately and specifically ignoring a most important part of the scientific method, which is that we're actually trying to work out causality, it isn't enough to note correlation and then blame all on the fashionable phlogiston of the day.   

You know, The Lancet?