Comparing cholesterol in different age groups
The healthcare system is not too worried about your risk of heart disease until you reach middle age, but the risk starts earlier in life and your arteries begin to silt up even in adolescence, and a recent study suggests it’s worth checking the level of your bad cholesterol when you’re in your 30s.
Guest: Dr Yiyi Zhang
Asst Prof, Dept Medicine
Columbia University, New York
Host: Dr Norman Swan
Producer: Diane Dean
Duration: 6min 43sec
The healthcare system doesn’t really get too concerned about your risk of heart disease until you are middle-aged. The way doctors are supposed to assess that risk is bringing together your age, your blood pressure, your cholesterol levels, your family history, and other factors like diabetes, to work out what might need to be done to avoid a heart attack or a stroke over the next five or ten years. But the risk starts earlier in life, and your arteries begin to silt up even in adolescence, and the question is whether it’s worth checking the level of your bad cholesterol, say when you are in your 30s. A recent study suggests it might. Dr Yiyi Zhang is a researcher at Columbia University’s medical centre in New York.
Yiyi Zhang: Thank you for having me.
Norman Swan: This is something I’ve often wondered about because normally what happens is that you measure your cholesterol when you are, say, 40 or 50 and you might do a total risk score on you. What you are really trying to measure is what’s the effect of higher than average levels early on in just blocking your arteries progressively over time.
Yiyi Zhang: Yes, exactly. So the majority of the previous studies looking at LDL usually focused on one single measure usually at middle or older age, but some evidence perhaps suggests that the cumulative burden of LDLC is actually also associated with cardiovascular disease risk, in addition to someone’s current LDL level. So that’s what our study is trying to look at, whether your cumulative exposure early on in your lifetime, does that independently associate with our CVD risk later in life.
Norman Swan: And CVD being cardiovascular disease. So what did you do in this study?
Yiyi Zhang: We did an observational study pulling together four large US cohorts and we looked at three different LDL cholesterol measurements, one being the cumulative exposure of LDL during young adulthood and middle age. And the other one is the time weighted average of LDL levels between this time period, which is the cumulative LDL level divided by the time duration during this period. And the last one is the LDL slope, which is how fast your LDL changed from young adulthood to middle age. So we look at three different things and whether they associate with coronary heart disease, stroke or heart failure risk, independent of someone’s LDL level at midlife.
Norman Swan: And these are groups of people that you’ve been following since young age or youngish age, they’ve had lots of physical examinations, you know their history, and they are healthy when you start off and you watch how they develop through the years, so you’ve got all these measures sitting away, and I think you had over 18,000 people included when you combined all these people.
Yiyi Zhang: Right, we have a large sample size, but some of the participants we have measurements starting from a really young, young age, but for most of them we actually started measurement during or around middle age. And what we did is we imputed their young adulthood LDL level using some statistical methods and to estimate their cumulative burden of LDLC during this younger age period.
Norman Swan: So you had some people who started young, you had some people who started in middle age in terms of the measurements, and you took what you learned from the young people and applied it to the middle-aged people in retrospect. What did you find?
Yiyi Zhang: So what we found is that on cumulative LDL level and also time weighted LDL level during young adulthood and middle-age were associated with an increased risk of coronary heart disease, and this association is independent of someone’s LDL level at middle age.
Norman Swan: So can you quantify the risk in terms of how long you’ve got raised LDL and how raised it’s got to be?
Yiyi Zhang: Some previous studies suggests there may be a threshold for cumulative LDL, but our study found that there really is no threshold. So the risk looks like it’s cumulative. And if we really want to put a threshold, it seems that at least with time weighted average LDL, the risk starts to increase at LDL level at about 100 micrograms per decilitre, which is not very high.
Norman Swan: So what is a primary care practitioner to do? Are you supposed to now start measuring people’s cholesterol earlier on in life or what?
Yiyi Zhang: I think the findings from our study may suggest that it’s time to consider incorporating serial LDL measure or the cumulative burden of LDL into clinical practice, because currently clinical decisions are mainly guided by someone’s contemporary LDL levels.
Norman Swan: So it’s a new thing for 30-year-olds and 40-year-olds, for example?
Yiyi Zhang: Yes, obviously more study is needed to see how many measures you will need to get a relatively reliable LDL trajectory or estimation of cumulative LDL burden, but at least our study suggests it’s time to start a conversation and start to think how we can incorporate these serial measures into clinical decision-making.
Norman Swan: In Australia, and I’m sure in some health maintenance organisations in the United States, you don’t make a treatment decision just based on your LDL level, you do it on your total risk, so are you a smoker, is there a strong family history, your age, age is very important. So they predict your risk of a heart attack or a stroke in the next five or ten years. When you are 30 years old, even with a high LDL your chances of a stroke or a heart attack are infinitesimally small in the next 10 or 15 years, and you wouldn’t qualify for treatment. What’s the intervention when you find that you might have a 30-year-old who is tracking with a higher than average LDL level?
Yiyi Zhang: I think this is really an excellent question and it’s the same thing in the US. So the current cholesterol guideline largely recommends starting base on the basis of someone’s 10-year risk of cardiovascular disease. And as a consequence, as you mentioned young adults usually are not eligible for statins and they are only eligible if they really have extremely high LDLC, for example above 190. So maybe one thing to consider is instead of using a 10-year risk score for young adults we may need to think something else, maybe a lifetime risk score or a longer-term risk score.
And also to your question, I think the first line of treatment always should be lifestyle intervention. However, for some people, diet and other lifestyle modification may not be sufficient. So for these young individuals, should we consider treating them early in life when it’s maybe more effective to prevent cardiovascular disease in later life? It’s a question for the policymaker.
Norman Swan: Yes, I’m sure the pharmaceutical industry would just love to know what the answer is. Yiyi, thank you very much for joining us.
Yiyi Zhang: Thank you for having me.
Norman Swan: Zhang is in the division of general medicine at Columbia University Medical Centre in New York.