"Controversial report claims there's no link between 'bad cholesterol' and heart disease," the Daily Mail reports, while The Times states: "Bad cholesterol 'helps you live longer',".
The headlines are based on a new review which aimed to gather evidence from previous observational studies on whether LDL cholesterol (so-called "bad cholesterol") was linked with mortality in older adults aged over 60. The conventional view is that having high LDL cholesterol levels increases your risk of dying of cardiovascular diseases, such as heart disease.
Researchers chose 30 studies in total to analyse. 28 studies looked at the link with death from any cause. Twelve found no link between LDL and mortality, but 16 actually found that lower LDL was linked with higher mortality risk – the opposite to what was expected.
Only nine studies looked at cardiovascular mortality link specifically – seven found no link and two found the opposite link to what was expected.
However, there are many important limitations to this review. This includes the possibility that the search methods may have missed relevant studies, not looking at levels of other blood fats (e.g. total and HDL cholesterol), and the possibility that other health and lifestyle factors are influencing the link.
Most importantly, as the researchers acknowledge, these findings do not take account of statin use, which lowers cholesterol. People found to have high LDL cholesterol at the study's start may have subsequently been started on statins, which could have prevented deaths.
The study was carried out by researchers from the University of South Florida, the Japan Institute of Pharmacovigilance and various other international institutions in Japan, Sweden, UK, Ireland, US and Italy.
Four of the study authors have previously written book(s) criticising "the cholesterol hypothesis". It should also be noted that nine of the authors are members of THINCS – The International Network of Cholesterol Skeptics. This is described as a group of scientists who "oppose…that animal fat and high cholesterol play a role [in heart disease]".
If you were playing Devil's Advocate, you could argue that this represents a preconceived view of the authors regarding the role of cholesterol, rather than the open, unbiased mind you would hope for in the spirit of scientific enquiry. That said, many important scientific breakthroughs happened due to the efforts of individuals who challenged a prevailing orthodoxy of thinking.
In general, the UK media provided fairly balanced reporting, presenting both sides of the argument – supporting the findings, but with critical views from other experts.
It has long been thought that cholesterol is a key cause of the fatty build-up in arteries (atherosclerosis) that causes heart disease. However, the researchers say there are contradictions to this view. Recent research has suggested that total cholesterol becomes less of a risk factor for all-cause or cardiovascular mortality the older people get. Less is known about LDL specifically and that's what this research aimed to look at.
A systematic review is the best way of gathering evidence from cohort studies that have looked at the link between an exposure or risk factor and an outcome. However, the strength of a review's findings is only as good as the studies they include. In cohort studies, it is often difficult to directly attribute an outcome to a specific cause, and there is always the potential that other factors are influencing the outcome.
The researchers searched one literature database (PubMed) in December 2015 to identify English-language cohort studies that had included a general population sample aged 60 and over. Studies had to have taken baseline measures of LDL cholesterol and then followed participants up over time, looking at the link with all-cause or cardiovascular mortality.
Three authors reviewed potential studies and extracted data. From an initial 2,894 hits, 19 publications, covering 30 cohorts and including 68,094 participants, were included. The majority of studies were excluded outright, as they didn't seem to contain anything relevant in the study title or abstract (summary). The other reasons for exclusion were non-English language, participants not being representative of the general population, not measuring LDL cholesterol at baseline, and not giving separate data for older adults or looking at mortality outcomes.
Overall, they reported that 16 cohorts (representing 92% of individuals in the review) of 28 examining all-cause mortality found an inverse relationship between LDL cholesterol and all-cause mortality. That is, as LDL cholesterol went down, all-cause mortality went up – higher LDL was apparently linked to lower all-cause mortality. In 14 of these 16, this was said to be a statistically significant link. The remaining 12 cohorts found no link with all-cause mortality.
Only nine of the identified cohorts specifically reported cardiovascular mortality. Seven found no link between LDL cholesterol and cardiovascular mortality. The other two found that those in the lowest fourth (quartile) of LDL levels actually had the highest cardiovascular mortality.
The researchers concluded that, "High LDL-C is inversely associated with mortality in most people over 60 years". They said their finding contradicts the cholesterol hypothesis: that cholesterol, particularly LDL, causes fatty build-up in the arteries.
They consider that as they found older adults with high LDL live just as long as those with low LDL, this "provides the rationale for a re-evaluation of guidelines recommending pharmacological reduction of LDL-C in the elderly".
This research suggests that – contrary to common belief – LDL cholesterol is not as "bad" as may be thought, and higher levels are not linked to all-cause or cardiovascular mortality.
However, before accepting this as fact, there are many important limitations to consider – both to the review and the included studies – many of which the review authors themselves acknowledge:
The findings of this review and possible explanations will need to be explored further, but for now this review doesn't provide solid evidence that high LDL cholesterol is good for you, or that statins are of no help. People given statins should continue to take them as prescribed.
"Fat is actually good for you" may be a great headline for a newspaper, and there are always researchers who are willing to make such a case, as we saw with the recent National Obesity Forum report.
These types of stories are often based on a selective view of evidence, rather than a comprehensive systematic review. There is currently no comprehensive body of evidence that contradicts current official advice on saturated fat consumption – which recommends no more than 30g of saturated fat a day for men and 20g for women.