The veterans study (Bowe et al, below) is not the first time a U-shaped association has been found for HDL levels and mortality.
Moradi et al, 2014. Elevated high-density lipoprotein cholesterol and cardiovascular mortality in maintenance hemodialysis patients. Nephrology Dialysis Transplantation, p.gfu022.
Bowe et al, 2016. High density lipoprotein cholesterol and the risk of all-cause mortality among US veterans. Clinical Journal of the American Society of Nephrology, pp.CJN-00730116.
Anyone who's followed clinical trials and Mendelian randomization studies should have doubts about a causal role for HDL in lowering CVD risk
Briel et al, 2009. Association between change in high density lipoprotein cholesterol and cardiovascular disease morbidity and mortality: systematic review and meta-regression analysis. Bmj, 338, p.b92.
Frikke-Schmidt et al, 2008. Association of loss-of-function mutations in the ABCA1 gene with high-density lipoprotein cholesterol levels and risk of ischemic heart disease. Jama, 299(21), pp.2524-2532.
Haase et al, 2011. LCAT, HDL cholesterol and ischemic cardiovascular disease: a Mendelian randomization study of HDL cholesterol in 54,500 individuals. The Journal of Clinical Endocrinology & Metabolism,97(2), pp.E248-E256.
Voight et al, 2012. Plasma HDL cholesterol and risk of myocardial infarction: a mendelian randomisation study. The Lancet, 380(9841), pp.572-58
Holmes et al, 2014. Mendelian randomization of blood lipids for coronary heart disease. European heart journal, p.eht571.
I don't believe these consistent results casting doubt on a causal role for HDL can all be explained by a U-shaped response curve. A number of lifestyle behaviors and dietary elements that increase HDL (aerobic exercise, weight loss, moderate alcohol consumption, monounsaturated fats, long-chain omega-3s, and soluble fiber) are believed to exert protective benefits by mechanisms independent from cholesterol efflux. The past association of low HDL and HDL/LDL ratios with risk may be a coincident marker of their absence. Likewise, some HDL and HDL/LDL ratio elevating fatty acids (laurate and myristate) are known to have negative inflammatory or vascular effects independent from their effects on cholesterol levels. Increased risk at the high end may reflect their intake.
There aren't many studies which have found negative effects from elevated HDL, but I always respect studies where the researchers are scratching their heads more than the ones with expected results:
Huang et al, 2012. Moderate to high concentrations of high-density lipoprotein from healthy subjects paradoxically impair human endothelial progenitor cells and related angiogenesis by activating Rho-associated kinase pathways. Arteriosclerosis, thrombosis, and vascular biology, 32(10), pp.2405-2417.
Edited by Darryl, 31 August 2016 - 10:39 PM.