Sausages, steaks, and socioeconomic status

A story in the news today tells us that sausages (and indeed other kinds of processed meats) increase your risk of cardiovascular disease, whereas steaks (and other forms of unprocessed read meats) do not. This is based on a study published in Circulation, which rather annoyingly, is behind a paywall, so I haven't read the full paper. The study was done at the Harvard School of Public Health, and shame on them for not making their research freely available in an open-access journal.

I have my doubts about the conclusions of this study. One of the most important predictors of cardiovascular disease risk is socioeconomic status. Put bluntly, rich people are less likely to develop cardiovascular disease than poor people.

I wonder if these results could be the result of confounding by socioeconomic status? My guess is that rich people are more likely to eat steaks and poor people are more likely to eat burgers. I don't know whether the analysis adjusted for socioeconomic status, as the paper is not freely available, but given that it was a meta-analysis (which, by an amazing coincidence, happens to be an anagram of "meat analysis") of 20 studies, I suspect that such adjustment wasn't universal. Even if all studies did adjust for it, socioeconomic status is extraordinarily hard to measure precisely. It's often done by grouping people into a small number of broad categories (which could mask important differences between the richest and the poorest within a category), or by data on postcode areas, which is also a very crude method. No doubt even if it was adjusted for, there would still be some residual confounding.

It's also rather intriguing to read that, although 20 studies were included in the paper overall, only 4 were included in the analysis of cardiovascular disease risk. There may be a legitimate reason for that, but there may equally be a reason that would make the results seem less trustworthy. Without reading the full paper, I don't know.

As it happens, I was planning to have sausages for my dinner this evening. I won't be changing that plan based on the results of this study.