Blood Lipid Levels Linked to IHD Mortality in Older Men

July 12, 2007 — Blood lipid levels, other than total cholesterol, are associated with ischemic heart disease (IHD) in older men, a new study has shown. While there was no association between total cholesterol and mortality in the overall cohort, total cholesterol levels were positively associated with IHD mortality in men without prior cardiovascular disease, report investigators, and cholesterol fractions were the strongest predictors of IHD mortality risk.
"Although total cholesterol is the most widely used blood test for prediction of IHD risk in the overall population, this study demonstrated that it had the least extreme hazard ratio for IHD mortality when used alone," write lead investigator Dr Robert Clarke (University of Oxford, UK) and colleagues in the July 9, 2007, issue of the Archives of Internal Medicine. "In contrast, the ratios of total cholesterol/HDL-C or apoB/apoA-1 were strong predictors of IHD mortality in all men, irrespective of the age at which plasma lipid levels were measured."
The analysis, according to investigators, was intended to compare the strength and association of mortality in relation to total cholesterol, various cholesterol fractions, and lipoproteins. Writing in the journal, the Oxford researchers note that although there is a strong and graded association between IHD and blood lipid concentrations in middle-aged individuals, there is uncertainty about that association in older individuals.
The investigators assessed IHD mortality associations with blood lipid levels in 5344 men, mean age 76 years. Of these, approximately 75% did not have cardiovascular disease, nor were they taking statins, while the remaining 25% did have cardiovascular disease or were taking statins. Over the seven-year follow-up period, there were 447 deaths, and hazard ratios were estimated for a two-standard-deviation difference in usual plasma lipid levels.
Investigators report that a lack of association of IHD mortality with total cholesterol levels in all men masked a positive association in men without prior cardiovascular disease or statin use and a nonsignificant inverse association in men with prior cardiovascular disease. Strong positive associations between IHD mortality and LDL- and apoB-cholesterol levels were observed in men without prior disease, but not in those with cardiovascular disease. IHD mortality was inversely associated with HDL-cholesterol levels and with apoA-1 levels in all men, and these associations were similar in men with and without cardiovascular disease.
The total cholesterol/HDL cholesterol and apoB/apoA-1 ratios were also strong predictors of IHD in all men, and these two lipid ratios were the strongest lipid predictors in men without cardiovascular disease. Because the ratios were strong predictors of risk, strategies to raise apoA-1 levels through physical exercise or weight loss might be associated with even greater benefits than those achieved by lowering apoB levels, write the authors.
With the uncertainty of the importance of blood lipid levels for IHD risk prediction in older patients, Clarke and colleagues point out that cholesterol-lowering therapy is not routinely prescribed in older populations. A recent Canadian study, for example, showed that only one in five older persons with cardiovascular disease were prescribed statin therapy, despite the proven benefits of lowering cholesterol levels in older patients observed in the Cholesterol Treatment Trialists' Collaboration.
Arch Intern Med. 2007;167:1373-1378.