Lipid hypothesis

This article is about the health risks of blood cholesterol. For the risks of saturated fat, see Saturated fat and cardiovascular disease.

The lipid hypothesis (also known as the cholesterol hypothesis) is a medical theory postulating a link between blood cholesterol levels and the occurrence of cardiovascular disease. A summary from 1976 described it as: "measures used to lower the plasma lipids in patients with hyperlipidemia will lead to reductions in new events of coronary heart disease".^[1] It states, more concisely, that "decreasing blood cholesterol [...] significantly reduces coronary heart disease".^[2]

As of 2023, there is international clinical acceptance of the lipid hypothesis.^[3][4][5][6]

History

In 1856, the German pathologist Rudolf Virchow first described lipid accumulation in arterial walls,^[7] however the initial connection between arteriosclerosis and dietary cholesterol would not be established until the research of Russian pathologist Nikolay Anichkov, prior to World War I.^[8] In 1913, a study by Anichkov showed that rabbits fed on cholesterol developed lesions in their arteries similar to atherosclerosis, suggesting a role for cholesterol in atherogenesis.^[9]

Dutch physician Cornelis de Langen noted the correlation between nutritional cholesterol intake and incidence of gallstones in Javanese people in 1916.^[10][11] de Langen showed that the traditional Javanese diet, poor in cholesterol and other lipids, was associated with a low level of blood cholesterol and low incidence of cardiovascular disease (CVD), while the prevalence of CVD in Europeans living in Java on a Western diet was higher.^[10] Since de Langen published his results only in Dutch, his work remained unknown to most of the international scientific community until the 1940s and 1950s.^[10] By 1951, it was accepted that, although the causes of atheroma were still unknown, fat deposition was a major feature of the disease process. "The so-called fatty flecks or streaks of arteries are the early lesions of atherosclerosis and... may develop into the more advanced lesions of the disease."^[12]

Ancel Keys and the Seven Countries Study

Ancel Keys

Main article: Ancel Keys

With the emergence of CVD as a major cause of death in the Western world in the middle of the 20th century, the lipid hypothesis received greater attention. In the 1940s, a University of Minnesota researcher, Ancel Keys, postulated that the apparent epidemic of heart attacks in middle-aged American men was related to their mode of life and possibly modifiable physical characteristics. He first explored this idea in a group of Minnesota business and professional men that he recruited into a prospective study in 1947, the first of many cohort studies eventually mounted internationally. The first major report appeared in 1963 and the men were followed through until 1981.^[13] After fifteen years follow-up, the study confirmed the results of larger studies that reported earlier on the predictive value for heart attack of several risk factors: blood pressure, blood cholesterol level, and cigarette smoking.^[13]

Seven Countries Study

Main article: Seven Countries Study

Keys presented his diet-lipid-heart disease hypothesis at a 1955 expert meeting of the World Health Organization in Geneva.^[14] In response to criticism at the conference, Keys recruited collaborating researchers in seven countries to mount the first cross-cultural comparison, the years-long Seven Countries Study, which is still under observation today. This was to compare the heart attack risk in populations of men engaged in traditional occupations and being from cultures with different diets, especially in the proportion of fat calories of different composition.^[15] There was also criticism before the study began: Yerushalmy and Hilleboe pointed out that Keys had selected for the study the countries that would give him the results he wanted, while leaving out data from sixteen countries that would not; they also pointed out that Keys was studying a "tenuous association" rather than any possible proof of causality.^[16] Keys then joined the nutrition committee of the American Heart Association (AHA), successfully promulgated his idea, and in 1961 the AHA became the first group anywhere in the world to advise cutting back on saturated fat (and dietary cholesterol) to prevent heart disease.^[17] This historic recommendation was reported on the cover of Time Magazine in that same year.^[18]

The Seven Countries Study was formally started in fall 1958 in Yugoslavia. In total, 12,763 males, 40–59 years of age, were enrolled in seven countries, in four regions of the world (United States, Northern Europe, Southern Europe, Japan). One cohort is in the United States, two cohorts in Finland, one in the Netherlands, three in Italy, five in Yugoslavia (two in Croatia, and three in Serbia), two in Greece, and two in Japan. The entry examinations were performed between 1958 and 1964 with an average participation rate of 90%, lowest in the US, with 75% and highest in one of the Japanese cohorts, with 100%.^[19]

Keys' book Eat Well and Stay Well ^[20] popularized the idea that reducing the amount of saturated fat in the diet would reduce cholesterol levels and the risks of serious diseases due to atheroma.^[21] Keys was followed during the rest of the 20th century by an accumulation of work that repeatedly demonstrated associations between cholesterol levels (and other modifiable risk factors including smoking and exercise) and risks of heart disease. These led to the acceptance of the lipid hypothesis as orthodoxy by much of the medical community.^[22] By the end of the 1980s, there were widespread academic statements that the lipid hypothesis was proven beyond reasonable doubt,^[23][24][25] or, as one article stated, "universally recognized as a law." ^{[26][27][28][29][30]}

Consensus

The medical consensus supports the lipid hypothesis as evidence from separate meta-analyses, prospective epidemiologic studies and randomized clinical trials have demonstrated that elevated levels of LDL blood cholesterol are a significant risk factor for cardiovascular disease.^[3]

The National Lipid Association have stated that by 2012, a wealth of evidence including numerous clinical trials examined by the Cholesterol Treatment Trialists' Collaboration has confirmed the lipid hypothesis.^[31] Too much LDL (called 'bad cholesterol') can lead to fatty deposits building up in the arteries which increases the risk of cardiovascular disease. A 2017 consensus statement from the European Atherosclerosis Society concluded that "consistent evidence from numerous and multiple different types of clinical and genetic studies unequivocally establishes that LDL causes ASCVD."^[3] The consensus statement noted:

Most publications that question the causal effect of LDL on the development of ASCVD tend to cite evidence from individual studies or a small group of highly selected studies, often without a quantitative synthesis of the presented evidence. Therefore, to avoid this type of selection bias, we have based our conclusions on the totality of evidence from separate meta-analyses of genetic studies, prospective epidemiologic studies, Mendelian randomization studies, and randomized clinical trials. This evidence base includes over 200 studies involving over 2 million participants with over 20 million person-years of follow-up and more than 150 000 cardiovascular events. Together these studies provide remarkably consistent and unequivocal evidence that LDL causes ASCVD.^[3]

A review from the Journal of the American College of Cardiology in 2018 concluded:

The causal effect of LDL and other apo B–containing lipoproteins on the risk of cardiovascular disease is determined by both the magnitude and the cumulative duration of exposure to these lipoproteins. The goal of maintaining optimal lipid levels throughout life is to keep the concentration of circulating LDL and other apo B–containing lipoproteins low to minimize the number of particles that become retained in the arterial wall and thereby minimize the rate of progression of atherosclerotic plaques.^[32]

The 2021 Canadian Cardiovascular Society Guidelines say "We recommend that for any patient with triglycerides > 1.5 mmol/L, non-HDL-C or ApoB be used instead of LDL-C as the preferred lipid parameter for screening (Strong Recommendation, High-Quality Evidence)".^[33]

The European Society of Cardiology have noted:

For almost a century, evidence has been overwhelming that lipids and diet are related and have a negative impact on CVD. It is also clear that lipids, and especially LDL, play a crucial role in atherosclerosis. However, groups of “non-believers” decelerated developments and clinical progress, sometimes for decades.^[34]

In 2023, the World Heart Federation published a report which stated that high levels of low-density lipoprotein (LDL) cholesterol are a major risk factor for cardiovascular diseases and that elevated LDL cholesterol contributed to 3.8 million deaths in 2021.^[6]

Contrary positions

The lipid hypothesis has been criticized by Uffe Ravnskov and colleagues.^[35][36] The most vocal critics of the lipid hypothesis are affiliated to the International Network of Cholesterol Skeptics (THINCS). These critics have been coined "cholesterol deniers" by British newspaper The Guardian.^[37]

See also

• Hypercholesterolemia
• Lipid-lowering agent
• Fatty acid ratio in food

References

1. Ahrens EH Jr (July 1976). "The management of hyperlipidemia: whether, rather than how". Ann Intern Med. 85 (1): 87–93. doi:10.7326/0003-4819-85-1-87. PMID 779574.
2. Steinberg D (2006). "An interpretive history of the cholesterol controversy, part IV: The 1984 coronary primary prevention trial ends it - almost". J Lipid Res. 47 (1): 1–14. doi:10.1194/jlr.R500014-JLR200. PMID 16227628.
3. Ference BA, Ginsberg HN, Graham I, et al. (August 2017). "Low-density lipoproteins cause atherosclerotic cardiovascular disease. 1. Evidence from genetic, epidemiologic, and clinical studies. A consensus statement from the European Atherosclerosis Society Consensus Panel". European Heart Journal. 38 (32): 2459–2472. doi:10.1093/eurheartj/ehx144. PMC 5837225. PMID 28444290.
4. Linton MF, Yancey PG, Davies SS, et al. (3 January 2019). "The Role of Lipids and Lipoproteins in Atherosclerosis". Endotext.
5. Duarte Lau F, Giugliano RP (July 2022). "Lipoprotein(a) and its Significance in Cardiovascular Disease: A Review". JAMA Cardiology. 7 (7): 760–769. doi:10.1001/jamacardio.2022.09. PMID 35583875.
6. "World Heart Report 2023: Confronting the World's Number One Killer" (PDF). World Heart Federation. 2023. Retrieved 22 January 2024.
7. Virchow, Rudolf (1856). "Gesammelte Abhandlungen zur wissenschaftlichen Medizin". Vierteljahrschrift für die praktische Heilkunde. Germany: Staatsdruckerei Frankfurt. Phlogose und Thrombose im Gefäßsystem.
8. Steinberg, Daniel (21 April 2004). "Thematic review series: The Pathogenesis of Atherosclerosis. An interpretive history of the cholesterol controversy: Part I". Journal of Lipid Research. 45 (9): 1583–1593. doi:10.1194/jlr.R400003-JLR200. PMID 15102877.
9. Steinberg, Daniel (2013). "In celebration of the 100th anniversary of the lipid hypothesis of atherosclerosis". Journal of Lipid Research. 54 (11): 2946–2949. doi:10.1194/jlr.R043414. PMC 3793599. PMID 23975896.
10. Blackburn, Henry (2012). "20th-Century "Medical Marco Polos" in the Origins of Preventive Cardiology and Cardiovascular Disease Epidemiology". The American Journal of Cardiology. 109 (5): 756–767. doi:10.1016/j.amjcard.2011.10.038. PMID 22470931.
11. de Langen, Cornelis (1916). "Cholesterine-stofwisseling en rassenpathologie". Geneeskundig Tijdschrift voor Nederlandsch-Indie (in Dutch). 56: 1–34.
12. Duff GL, McMillan GC (1951). "Pathology of atherosclerosis". Am J Med. 11 (1): 92–108. doi:10.1016/0002-9343(51)90011-3. PMID 14837929.
13. Keys, Ancel; Taylor, Henry Longstreet; Blackburn, Henry; et al. (1 September 1963). "Coronary Heart Disease among Minnesota Business and Professional Men Followed Fifteen Years". Circulation. 28 (3): 381–95. doi:10.1161/01.cir.28.3.381. PMID 14059458.
14. Famous Polemics on Diet-Heart Theory. Henry Blackburn, School of Public Health, University of Minnesota. http://www.epi.umn.edu/cvdepi/essay.asp?id=33 accessed 18 March 2014
15. Keys, Ancel (1980). Seven Countries: A Multivariate Analysis of Death and Coronary Heart Disease. Harvard University Press. ISBN 978-0-674-80237-7.
16. Yerushalmy J, Hilleboe HE (1957). "Fat in the diet and mortality from heart disease. A methodologic note". NY State J Med. 57: 2343–54.
17. "Dietary Fat and Its Relation to Heart Attacks and Strokes". JAMA. 175 (5): 389–391. 4 February 1961. doi:10.1001/jama.1961.63040050001011. PMID 14447694.
18. "TIME Magazine Cover: Ancel Keys". TIME.com. 13 January 1961. Retrieved 23 July 2017.
19. Keys A (Ed). Seven Countries: A multivariate analysis of death and coronary heart disease. Harvard University Press. Cambridge, Massachusetts. 1980. ISBN 0-674-80237-3.
20. Keys, Ancel (1959). Eat Well and Stay Well. United States: Doubleday. ISBN 978-0-385-06575-7.
21. . The American Physiological Society. Archived from the original on 27 September 2007. Retrieved 15 April 2007.
22. Steinberg D (2006). "Thematic review series: the pathogenesis of atherosclerosis. An interpretive history of the cholesterol controversy, part V: the discovery of the statins and the end of the controversy". J. Lipid Res. 47 (7): 1339–51. doi:10.1194/jlr.R600009-JLR200. PMID 16585781.
23. Steinberg D (1989). "The cholesterol controversy is over. Why did it take so long?". Circulation. 80 (4): 1070–1078. doi:10.1161/01.cir.80.4.1070. PMID 2676235.
24. LaRosa JC (1998). "Cholesterol & atherosclerosis: a controversy resolved". Adv Nurse Pract. 6 (5): 36–37. PMID 9633288.
25. Steinberg D (2002). "Atherogenesis in perspective: hypercholesterolemia and inflammation as partners in crime". Nature Medicine. 8 (11): 1211–1217. doi:10.1038/nm1102-1211. PMID 12411947. S2CID 30459713.
26. Thompson GR, Packard CJ, Stone NJ (2002). "Goals of statin therapy: three viewpoints". Curr Atheroscler Rep. 4 (1): 26–33. doi:10.1007/s11883-002-0059-6. PMID 11772419. S2CID 72257114.
27. Bucher, HC; Griffith, LE; Guyatt, GH (February 1999). "Systematic review on the risk and benefit of different cholesterol-lowering interventions". Arteriosclerosis, Thrombosis, and Vascular Biology. 19 (2): 187–195. doi:10.1161/01.atv.19.2.187. PMID 9974397.
28. Tyroler HA (1987). "Review of lipid-lowering clinical trials in relation to observational epidemiologic studies". Circulation. 76 (3): 515–522. doi:10.1161/01.cir.76.3.515. PMID 3304704.
29. Brown WV (1990). "Review of clinical trials: proving the lipid hypothesis". Eur Heart J. 11 Suppl H: 15–20. doi:10.1093/eurheartj/11.suppl_h.15. PMID 2073909.
30. Kroon AA, Stalenhoef AF (1997). "LDL-cholesterol lowering and atherosclerosis -- clinical benefit and possible mechanisms: an update". Neth J Med. 51 (1): 16–27. doi:10.1016/S0300-2977(97)00031-4. hdl:2066/26174. PMID 9260486. S2CID 7075128.
31. "The Lipid Hypothesis". lipid.org. Retrieved 22 January 2024.
32. Ference BA, Graham I, Tokgozoglu L, Catapano AL (2018). "Impact of Lipids on Cardiovascular Health: JACC Health Promotion Series". Journal of the American College of Cardiology. 72 (10): 1141–1156. doi:10.1016/j.jacc.2018.06.046. PMID 30165986. S2CID 52136486.
33. Pearson GJ, Thanassoulis G, Anderson TJ, et al. (August 2021). "2021 Canadian Cardiovascular Society Guidelines for the Management of Dyslipidemia for the Prevention of Cardiovascular Disease in Adults". The Canadian Journal of Cardiology. 37 (8): 1129–1150. doi:10.1016/j.cjca.2021.03.016. PMID 33781847.
34. Kuijpers PM (13 January 2021). "History in medicine: the story of cholesterol, lipids and cardiology". e-Journal of Cardiology Practice. 18 (9).
35. Ravnskov, Uffe; Diamond, David M.; Hama, Rokura; et al. (1 June 2016). "Lack of an association or an inverse association between low-density-lipoprotein cholesterol and mortality in the elderly: a systematic review". BMJ Open. 6 (6): e010401. doi:10.1136/bmjopen-2015-010401. ISSN 2044-6055. PMC 4908872. PMID 27292972. High LDL-C is inversely associated with mortality in most people over 60 years. This finding is inconsistent with the cholesterol hypothesis (ie, that cholesterol, particularly LDL-C, is inherently atherogenic). Since elderly people with high LDL-C live as long or longer than those with low LDL-C, our analysis provides reason to question the validity of the cholesterol hypothesis. Moreover, our study provides the rationale for a re-evaluation of guidelines recommending pharmacological reduction of LDL-C in the elderly as a component of cardiovascular disease prevention strategies.
36. Ravnskov, Uffe; de Lorgeril, Michel; Diamond, David M; et al. (3 October 2018). "LDL-C does not cause cardiovascular disease: a comprehensive review of the current literature". Expert Review of Clinical Pharmacology. 11 (10): 959–970. doi:10.1080/17512433.2018.1519391. ISSN 1751-2433. PMID 30198808. Our search for falsifications of the cholesterol hypothesis confirms that it is unable to satisfy any of the Bradford Hill criteria for causality.
37. Boseley, Sarah (30 October 2018). "Butter nonsense: the rise of the cholesterol deniers". The Guardian. ISSN 0261-3077. Retrieved 11 January 2024.