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For years we have seen HDL cholesterol as having a protective effect against cardiovascular disease. But could new scientific evidence found in 2017 prove this to be wrong?
Some of the earliest cholesterol studies from the 1950s found that high levels of HDL cholesterol were associated with lower rates of heart attack and stroke and that lower levels of HDL were associated with higher rates. Since then, the assumption has been that higher levels of HDL cholesterol are always protective against angina, heart attack and stroke.
To find out more about the different types of cholesterol, take a look at our cholesterol blog post.
Denmark, despite its small size, has some of the largest and best population-level surveys in the world. It is also a producer of some of the world’s tastiest pickled herrings, a great source of HDL cholesterol (full disclosure: my wife is part Danish!). So, when a Danish study in 2017 threw doubt on the health benefits of HDL cholesterol, it was time to question these long-held beliefs. The research looked at how rates of death from all causes, as well as from ischaemic cardiovascular disease (angina, heart attack and stroke) varied with levels of HDL cholesterol. The study looked at both very high and very low levels of HDL, and it did this on a large scale across more than 100,000 people. The findings for very low levels of HDL were as expected, people were more likely to die of all causes, but interestingly, people with very high levels of protective HDL cholesterol also died more frequently both from ischaemic cardiovascular disease.
Does this mean that people with high levels of HDL should be attempting to decrease their levels? It would be easy to jump to this conclusion, but we need to be careful in how we interpret this finding. The authors of the study point out that we could be seeing the effect of either genes or another disease, which increases both the risk of death and high HDL. This would mean that attempting to decrease your HDL levels may have no effect, and may even increase the risk of cardiovascular disease. Before we can begin to understand the relationship between HDL cholesterol and mortality any better, further research is needed.
Have LDL and non-HDL cholesterol been unfairly demonised as unhealthy?
The short answer to this question is no, as there is a large body of evidence which supports the hypothesis that they increase the risk of cardiovascular disease. But there have been some developments in 2017 which suggest that the risks of dietary saturated fats may have been overplayed and that sugar may play a greater role in cardiovascular disease development.
Scientists have been reviewing the history and documents of the Sugar Research Foundation (SRF), an organisation funded by the sugar industry to research the health effects of sugar. They describe a project funded by the SRF and performed by a team at Harvard which reviewed the health effects of diets rich in sugar, versus diets rich in saturated fat. In their analysis, they claim that the study deliberately understated the risks of diets rich in sugar, and overstated the risks of diets rich in saturated fats. While no evidence was found that the SRF directly edited the research paper, they state that they did find some evidence that the SRF influenced the report findings. So much of our current thinking about dietary saturated fats and sugar may be biased in favour of over-estimating the risks that saturated fats cause and underestimating the health risks of sugar.
So, does this mean that LDL cholesterol is a good thing? Absolutely not. However, it does mean that people who want to decrease their risk of cardiovascular disease should shift their focus from solely decreasing their intake of saturated fats to decreasing their intake of sugar as well. Eating less meat, dairy products and consuming more fruit and vegetables are effective ways to reduce saturated fat. The 7 a day campaign has been recommending this in response to findings that those with a high intake of vegetables and fruit were less likely to develop cardiovascular disease and cancer. The problem with this recommendation is that our brains’ reward centres are stimulated by eating foods rich in fat or sugar, so if fat intake is reduced there may be a temptation to compensate by increasing fruit (and therefore sugar) intake rather than vegetables. The greatest health benefits of the 7 a day approach were seen with high vegetable diets, the effect of fruit was less pronounced. So, if you’re planning to eat 7 a day in the New Year make sure that most of this is in the form of vegetables.
Cardiovascular risk prediction gets smarter
Professor Julia Hippisley Cox from the University of Nottingham has been studying how blood pressure, cholesterol, smoking and pre-existing illnesses can be used to predict the risk that they will develop cardiovascular disease in the future. Her QRisk algorithm was updated in 2017 to include new risk factors, some of these are common (migraine) and others less so (lupus). The QRisk tool lets you look at how likely you are to develop cardiovascular disease in the next 10 years. If you know your blood pressure and cholesterol levels, then I recommend taking a look at the QRisk3 website, just click here.
You will need your total cholesterol to HDL ratio; you can calculate this yourself by dividing your total cholesterol by your HDL level. People with a risk of greater than 10% should discuss this with their GP as they may need help to lower their cholesterol. I also recommend seeing how lowering blood pressure and weight affects your risk by entering lower numbers into the tool.
It’s not just cholesterol that can be a sign of cholesterol deposits.
When cholesterol deposits form in blood vessels, there is an increase in levels of inflammation. Measuring inflammation levels can give extra information to people who are trying to assess their level of cardiovascular risk. C-Reactive Protein (CRP) is produced whenever there is inflammation in the body; this can happen in response to injury or infection, as well as in response to atherosclerosis. A test that is more specific to the CRP produced by atherosclerosis has been developed. Increased levels of high sensitivity CRP have been shown to increase the likelihood of cardiovascular disease independently of the risk that cholesterol causes. They can be helpful when trying to work out whether to try and reduce cholesterol through diet or to use medication as well. Lp-PLA2 is another marker of inflammation that is associated with increased levels of inflammation.