"People as young as 25 'need to know of their bad cholesterol levels'," reports The Guardian.
A team of researchers developed a model that shows the risk of having a heart attack or stroke by age 75, for people of different ages, depending on their so-called "bad" cholesterol (non-high density lipoprotein, or non-HDL cholesterol).
Non-HDL cholesterol (which includes LDL cholesterol, as well as other types of "bad" cholesterol) raises the chances of developing cardiovascular diseases (CVD), including heart attack and stroke. But most current models used by doctors look at the risk over a 10-year period and apply this risk to people from middle age onwards.
For this study, researchers looked at 43 years of data from 398,846 people across Europe, Australia and the US, about 1 in 3 of whom were younger than 45 when first studied. This allowed researchers to create a model to predict very long-term risks of heart attack and stroke for younger people. The model also estimated how reducing non-HDL cholesterol would lower people's risk.
The impact of having a high level of non-HDL cholesterol on future cardiovascular risk by age 75 was most apparent for people under 45. That could be because of the effect of having high non-HDL cholesterol over decades of life and because younger people have more time to develop CVD than older people.
Diet and exercise are usually the first steps recommended to reduce your cholesterol level.
Find out about the causes of CVD.
Where did the story come from?
The researchers who carried out the study worked at 44 universities, hospitals or research institutions internationally, led by researchers at the University Heart and Vascular Centre Hamburg, Germany. The study was funded by the EU Framework Programme, UK Medical Research Council and German Centre for Cardiovascular Research. It was published in the peer-reviewed medical journal The Lancet.
The Guardian, The Times, BBC News and Mail Online did a good job of describing the complex study. However, Mail Online's statement that "higher cholesterol in under-45s is more dangerous than in over-60s", while true, is open to misinterpretation. High cholesterol was linked to a higher relative risk in younger people, but older people's absolute risk of heart attack or stroke in the short term is higher.
Absolute risk is your overall risk of something happening, while relative risk is your risk compared to someone else's risk.
What kind of research was this?
This was a risk evaluation and modelling study, using cohorts (groups of people). This type of study is useful to process large amounts of data to make predictions about how different risk factors might affect individuals. However, the predictions are only an estimate of risk – the actual risk for any individual is likely to be based on more than age and cholesterol level.
What did the research involve?
Researchers used data from 398,846 people who were part of 38 long-term cohort studies in Europe, the US and Australia. They excluded people who had cardiovascular disease at the start of the study.
They calculated people's non-HDL cholesterol when they entered the study, tracked how many years they had been in the study, and whether they had a cardiovascular event (such as heart attack or stroke). They then assessed the link between non-HDL cholesterol and risk of heart attack or stroke, adjusting the figures to take account of potential confounding factors including:
- body mass index (BMI)
- blood pressure
- use of cholesterol-lowering medicines
- total and HDL ("good") cholesterol
Researchers then used the results to construct a model which would estimate people's risk of having a heart attack or stroke by age 75. They used data from half the people in the study to construct the model, and from the other half to test the results.
In addition, they estimated how a person's risk would change if they reduced their non-HDL cholesterol levels by half.
What were the basic results?
The researchers found that people's non-HDL cholesterol raised their risk of having a heart attack or stroke throughout their lives. Increased non-HDL cholesterol had the biggest effect on lifetime risk of heart attack or stroke for people aged under 45.
Comparing people with the highest non-HDL cholesterol level (5.6mmol/L or above) to those with the lowest level (under 2.6mmol/L):
- women under 45 who had the highest level were 4.3 times more likely to go on to have a heart attack or stroke than women the same age with the lowest level (hazard ratio) (HR) 4.3, 95% confidence interval (CI) 3.0 to 6.1)
- men under 45 had similar results – those with the highest level were 4.6 times more likely to go on to have a heart attack or stroke than men the same age with the lowest level (HR 4.5, 95% CI 3.3 to 6.5)
- women aged 60 or older with the highest level had 1.4 times the risk of women the same age with the lowest level (HR 1.4, 95% CI 1.1 to 1.7)
- men aged 60 or older with the highest level had 1.8 times the risk of men the same age with the lowest level (HR 1.8, 95% CI 1.5 to 2.2)
The risk modelling tool predicted the range of risk according to whether they were smokers, had high blood pressure (hypertension), diabetes or obesity and found that:
- women under 45 with the highest cholesterol level would have a 14% to 24% risk of heart attack or stroke by age 75, compared to a 6% to 12% risk for those with the lowest level
- men under 45 with the highest cholesterol level would have a 30% to 43% risk of a heart attack or stroke by age 75, compared to 12% to 19% for those with the lowest level
- women 60 or over with the highest cholesterol level would have an 11% to 18% risk of a heart attack by age 75, compared to 5% to 8% for those with the lowest level
- men 60 or over with the highest cholesterol level would have a 20% to 32% risk of a heart attack or stroke by age 75, compared to 8% to 16% for those with the lowest level
The model also predicts people could reduce their risk substantially if they halved their cholesterol levels at any age.
How did the researchers interpret the results?
The researchers said: "Our study extends current knowledge because it suggests that increasing concentrations of non-HDL cholesterol predict long-term cardiovascular risk, particularly in cases of modest increase at a young age."
This complex study uses a lot of data, but the conclusions are fairly simple:
- high non-HDL cholesterol raises the risk of heart attack or stroke over the long term
- this elevated risk starts at a younger age than previously thought
- people should have their cholesterol tested in their 20s or 30s so they can consider taking steps to lower it
Because of the complexity of the mathematical modelling, we cannot test the accuracy of the predictions given by the modelling tool. It is important to remember that tools like this only give an estimated average of risk, and not an actual risk for any single individual.
There are limits to the study. As with all data collection from different sources, it is possible that some of the reporting of cardiovascular events may have been inaccurate. The studies measured cholesterol levels only once, so we do not know whether people's levels changed over time. The people in the study were mostly of European ancestry and from high-income countries in Europe, as well as the US and Australia, which means the results may not be applicable to people from other ethnic backgrounds or living in other countries.
The study does not mean that people with high cholesterol should necessarily start taking statins in their 30s. We do not know the effects of taking statins for such a long period for people who are otherwise healthy.
People in the UK are offered an NHS Health Check from age 40, which includes a cholesterol test. The first step in lowering non-HDL cholesterol is usually eating a healthier diet and doing more exercise, although some people may also be prescribed statins.
Find out more about cholesterol.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
The Times (subscription required), 4 December 2019
Mail Online, 4 December 2019
The Guardian, 3 December 2019
BBC News, 4 December 2019
Links to the science
The Lancet. Published online 3 December 2019