Personal Science Week - 240905 Arterial Plaque

An easy way to measure heart risk

My family history of high blood cholesterol has me watching for the warning signs of heart disease. But a personal scientist cares about the end result (heart disease), not the metric (cholesterol).

This week I tried an easy at-home method to check the hardness of my arteries.

My personal science mentor, Seth Roberts had LDL cholesterol over 150 mg/dL, considerably higher than the < 100 mg/dL that is considered optimal. If you tried to warn him of the dangers (as if he didn’t know!), he could overwhelm you with reasons that the research was inconclusive, wrong, or otherwise didn’t apply to him.

Seth, who was otherwise in perfect health, died unexpectedly of a heart attack at age 60. If he had treated his high cholesterol, would he be alive today?

The research is clear. On average, people with higher cholesterol have more heart disease. But this means little without more context. The first question I want to know is absolute, not relative, numbers. 

Here’s the data I found from AHA 2019

A 60-year-old man like Seth had a 10-15% chance of a heart attack even if his lipid numbers were normal. His higher LDLC doubled his risk, but he still had a 70% chance of making it to age 70 without any cardiac events. Those odds aren’t great, but come on: once you’re in your 60s, your health is going to deteriorate no matter what.

A very important note: Seth had a family history of heart disease (his father died even younger).  Even more important update: I’m reminded that Seth’s family had no history of heart disease—his father died at age 72. He also had at least two heart scans, both of which were roughly normal. Read all of his blog posts, with many more details here.

In other words, although cholesterol seems oddly correlated, it can’t be the whole story. I suspect we talk about cholesterol the most because the test is easy and cheap. The overall reasoning makes sense: too much blood cholesterol and, over time, it accumulates as fatty deposits that can clog the blood vessels. Lower cholesterol levels are less likely to accumulate. The logic can be refined by differentiating between “big” and “little” cholesterol particles, but directionally it’s pretty straightforward.

So if it’s the accumulation that causes problems, why not measure that? Who cares about the level of the cholesterol itself; why not look at the arteries? 

Yes, there are tests that claim to measure it more directly (CT scan, echo stress test, etc. ) but those cost hundreds of dollars. Of course that’s cheap if you really uncover a solvable problem, but the expense and trouble make it less likely you’ll test yourself frequently.

Ankle Brachial Index

Fortunately, it’s possible to test your arterial hardness levels at home using the Ankle Brachial Index. Using an at-home blood pressure cuff, measure the blood pressure of both arms and both ankles. Look up a chart at Ankle Brachial Pressure Index (ABPI): An update for practitioners.

I tested this using a $30 iHealth blood pressure monitor. You can buy these anywhere. (Be sure to get the “arm cuff” kind, not the supposedly-easier wrist kind)

My readings were pretty variable until I figured out how to align the air bladder with the artery, which can be tricky to find on the legs. Still, after multiple tries, here’s what I found: Right arm 93/72, right ankle 120/73, left ankle 116/82, left arm 97/73

Calculate the ankle brachial index (ABI) by dividing the higher of the ankle systolic pressures by the higher of the arm systolic pressures. In my case:

1. Highest arm systolic pressure: 97 (left arm)

2. Right ankle systolic: 120

3. Left ankle systolic: 116

Right ABI = 120 / 97 = 1.24 Left ABI = 116 / 97 = 1.20

“Normal” is anything between 0.9 and 1.3. 

My Right ABI (1.24) and Left ABI (1.20) both fall within the normal range.

Bonus conclusions:

1. No indication of PAD: My ABI results do not suggest peripheral artery disease in my legs.

2. Good blood flow: The results indicate good blood flow to my lower extremities.

3. Slight elevation: My ABIs are on the higher end of normal, which is often seen in physically active individuals or those with very flexible arteries.

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Important

If my ABI had been out of range, then I should immediately seek medical attention. This test, while not perfect, is a direct measure of potential pathologies and should be taken more seriously than a single cholesterol result.

This doesn’t mean I’m off the hook. I’ll need to continue watching all the parameters that matter for heart disease, because although a “normal” ABI is reassuring, cardiac disease is about more than just whatever this crude measure says about my arteries.

Still, it’s fast and easy and should be part of every personal scientist’s toolkit.

Personal Scientists of the Week

Environmental activist Brandy Deason put Airtags in her recycling waste to see if her city really was recycling plastic the way they claimed. tldr; no, her empty plastic bottles were just piling up at another storage facility, with none of the acclaimed benefits of recycling.

Nutrition scientist Lara Hyde ran a 10-week experiment to see how fermented food affect her microbiome. She did the full Viome gut/blood test before and after beginning an intensive regimen of 6 servings/day. tldr; no real difference once you take into account the margin of error on the test.

Alex Guzey reports his updated thoughts about LLMs, systematically tracking his thoughts about the future, and the existential risks purported to come with AI. I think his format—collect your opinions over time‚ is a great idea to apply to lots of areas of uncertainty. I keep a similar list of what I think about cholesterol (see above), or my straightforward off-the-cuff thoughts about major news events (COVID-19, Ukraine, Gaza, etc.). I find it very useful to go back in time and try to see what I got right and wrong.

Healthline’s comprehensive review of AG1. You know that Athletic Greens powder you hear advertised on lots of podcasts? tldr; at $3/day it’s an expensive way to get extra nutrition, but the reviewer thinks it might have helped a little on her n-of-1 test.

Speaking of AG1, our friends at Tastermonial have a new Substack where they use AG1 as an example of “borrowed science”. Supplements are especially guilty, often promoted based on a claim from some academic study, without pointing to the obvious ways that study doesn’t apply in this case.

Other Personal Science Links

You’ll soon be able to order 4 more free COVID tests. The US government has already distributed 900 million tests. Man do I wish I could have been one of the companies that makes those tests!

The Prism and Why You Are Probably An NPC : a breakdown of different ways people conform, including contrarians (“disillusioned conformists”), disciples, tribalists, averagers. He suggests dividing your own set of interests into primary, secondary, and tertiary concerns, and make an effort to only care about your primary ones: “On tertiary issues, be silent. On secondary issues, be humble. On primary issues, be passionate.”

I liked RFK Jr’s response after an interviewer suggested it would be a crisis if his side loses the election: “Nothing's a crisis, everything's a task”. Especially in an election year, be skeptical when people try to convince you that something-something is a “crisis” or an “existential risk”. The world will go on. Everything’s a task.

This week, paid subscribers can see my Unpopular Science overview of two new books, plus more thoughts about LLMs: I recently switched from ChatGPT to Claude Pro because I thought it would be better. Ask me in another month.

Meanwhile, if you have other topics you’d like to discuss, let us know