Editor—The key problem with the article by Hippisley-Cox and Coupland, who reported benefit from having been prescribed a statin, is outlined by a line in the discussion, according to which confounding by indication could have occurred if patients with a better prognosis were more likely to be prescribed different combinations of treatments.1
High, rather than low, cholesterol concentrations are linked with greater statin use, and this selects the high cholesterol group, in which early death from heart failure is less2 and general mortality in elderly patients is lower.3,4
It is therefore unfortunate that Hippisley-Cox and Coupland say that treatment including statins improves survival rather than emphasising the simple point of selection bias—that is, of not being in the “low cholesterol” group of elderly people, where increased mortality may well be concentrated and cholesterol lowering treatment was not indicated.
This cohort study could lead to “could have” medicine, whereas in a high risk population of virtually identical age, the placebo controlled PROSPER study (surprisingly omitted as reference) found absolutely no mortality benefit but increased cancer in a statin group with fewer smokers.5
Competing interests: None declared.
References
- 1.Hippisley-Cox J, Coupland C. Effect of combinations of drugs on all cause mortality in patients with ischaemic heart disease: nested case-control analysis. BMJ 2005;330: 1059-63. (7 May.) [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Horwich TB, Hamilton MA, Maclellan WR, Fonarow GC. Low serum total cholesterol is associated with marked increase in mortality in advanced heart failure. J Card Fail 2002;8: 216-24. [DOI] [PubMed] [Google Scholar]
- 3.Weverling-Rijnsburger AW, Blauw GJ, Lagaay AM, Knook DL, Meinders AE, Westendorp RG. Total cholesterol and risk of mortality in the oldest old. Lancet. 1997;350: 1119-23. [DOI] [PubMed] [Google Scholar]
- 4.Schatz IJ, Masaki K, Yano K, Chen R, Rodriguez BL, Curb JD. Cholesterol and all-cause mortality in elderly people from the Honolulu heart program: a cohort study. Lancet 2001;358: 351-5. [DOI] [PubMed] [Google Scholar]
- 5.Shepherd J, Blauw GJ, Murphy MB, Bollen EL, Buckley BM, Cobbe SM, et al. Pravastatin in elderly individuals at risk of vascular disease (PROSPER): a randomised controlled trial. Lancet 2002;360: 1623-30. [DOI] [PubMed] [Google Scholar]