Should We Be Concerned About Cholesterol or Not?
"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.
Cholesterol and heart disease – what is the evidence?
So what is the evidence that most health organisations – including the NHS, the World Health Organization, the British Dietetic Association, the British Heart Foundation and the United States Food and Drug Administration – have based their diet guidelines on?
Well, there are a number of very well conducted studies that suggest a clear link between high cholesterol levels and heart disease. A major review in The Lancet, involving nearly a million people, concluded that, "Total cholesterol was positively associated with IHD [heart disease] mortality."
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:
- There is the potential that many studies relevant to this question may have been missed out. The review searched only a single literature database, excluded studies only available in non-English language, and excluded studies where the title and abstract did not appear to contain information on the link between LDL and mortality in older adults.
- The study only looked at the link in older adults aged over 60. LDL-cholesterol levels may show different links with long-term mortality in younger adults. Though this was intended to represent the general older-age population, some studies had excluded people with specific conditions such as dementia, diabetes or terminal illness.
- The studies varied widely in adjustment for confounding factors that could be having an influence on the link between LDL and mortality. Age, gender and body mass index (BMI) were common factors that studies took into account, but others variably accounted for lifestyle factors (e.g. smoking, alcohol), socioeconomic factors, presence of conditions, and use of medications.
- Only LDL cholesterol was examined. Levels of total cholesterol, trigylcerides, and the ratio of LDL to HDL "good" cholesterol could be having an effect and mediating the link between LDL and mortality.
- Most of the evidence for this review is for the link with all-cause mortality – not cardiovascular mortality. High LDL-cholesterol is believed to be linked with the development of atherosclerosis and cardiovascular disease. This review does not provide enough firm evidence to refute this link. The review cannot with certainty explain the reasons for the apparent link between LDL levels and death from any cause – with roughly half of studies finding a link and half not.
- Importantly, the study does not provide evidence that statins are "a waste of time". These are not trials examining mortality between people prescribed statins or not. The researchers openly acknowledge that the use of statins – which they haven't directly examined – may be confounding the links in these studies. For example, the people found to have the highest LDL cholesterol levels at the study's start may have then been started on statins, and this could have dramatically cut their reduced mortality risk.
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.
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.
How Atherosclerosis Happens
This video shows and explains the process of atherosclerosis. Quite long at 13 minutes, but absolutely fascinating when you see all the little cells doing their jobs and getting into a right mess!
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