What if two over-the-counter supplements could more than halve your risk of dying from heart disease? In one well-known Swedish trial, that is roughly what happened. The catch is a detail most headlines skip, and it may decide whether the result applies to you at all.
The Trial: KiSel-10 in a Nutshell
The study is known as KiSel-10. It was published in the International Journal of Cardiology by Urban Alehagen and colleagues at Linköping University. It was a prospective, randomized, double-blind, placebo-controlled trial, the gold-standard design for testing an intervention.
- Who: 443 community-living Swedish citizens aged 70 to 88
- What: Either a combined supplement or a placebo, taken daily
- The supplement: 200 mg of coenzyme Q10 (CoQ10) plus 200 µg of selenium as selenized yeast
- How long: The abstract describes a 5-year trial with a follow-up of 5.2 years. Later papers from the group describe the active intervention period as 4 years.
Participants were checked every six months. The team ran clinical examinations, echocardiography and blood biomarker tests, and recorded deaths.
The rationale is that both selenium and CoQ10 are essential to cell function, and low cardiac levels of each have been reported in people with cardiomyopathy. Earlier trials tested the two separately and gave inconsistent results. The authors argued the two substances work together, and that combined supplementation had not been properly studied.
The Results: Three Signals Pointing the Same Way
1. Cardiovascular mortality. Over 5.2 years of follow-up, cardiovascular death occurred in 5.9% of the supplement group versus 12.6% of the placebo group (P=0.015). That is a relative reduction of a little over half. In absolute terms, the gap is about 6.7 percentage points.
2. NT-proBNP. This blood marker rises when the heart is under strain, and lower is generally better. At 48 months, average levels were 214 ng/L in the active group versus 302 ng/L with placebo (P=0.014).
3. Echocardiography. Heart ultrasound scans showed a significantly better cardiac function score in the supplement group (P=0.03).
The deaths, the blood marker and the imaging all moved in the same direction. That consistency makes the result harder to dismiss as a statistical fluke. The researchers used both intention-to-treat and per-protocol analyses and adjusted for potential confounders.
The Twist: Sweden Is Low in Selenium
Sweden, like much of Europe, has soils low in selenium, so the population's dietary intake tends to be modest. Baseline selenium in this cohort was about 67 µg/L, which is on the low side.
This matters because the trial may not have tested "CoQ10 plus selenium" in a general sense. It may have tested correcting a marginal selenium shortfall, with CoQ10 added. If you already get plenty of selenium, for example from a US diet or from Brazil nuts, the same benefit may not apply. The paper's results cannot tell us.
Who Might This Apply To?
Cautiously, the findings are most relevant to:
- Older adults (the trial enrolled ages 70 to 88)
- People living in low-selenium regions or eating low-selenium diets
- People whose selenium status is actually low, which a blood test can show
The trial was not designed to show that younger or selenium-replete people would benefit. Later follow-ups from the same group reported lower cardiovascular mortality persisting at 10 to 12 years. Those analyses are still based on the same cohort, so they are not independent confirmation.
The Fine Print
This is promising, but it is not settled science.
- Small sample: 443 people is modest, and the number of deaths is relatively small. Results with few events can swing widely and may not replicate.
- Manufacturer-supplied product: The supplements (SelenoPrecise and Bio-Quinone) were supplied by Pharma Nord. Industry supply is common in supplement research and does not invalidate the findings, but independent replication would add confidence.
- Can't separate the nutrients: The trial gave both together against placebo. It cannot say whether selenium, CoQ10 or the combination did the work.
- Single population: All participants were elderly Swedes. Results may not carry over to other groups.
- Selenium is a two-sided nutrient: More is not better. In the large SELECT trial, selenium supplementation raised a signal for type 2 diabetes. The commonly cited tolerable upper intake is 400 µg/day.
Practical Takeaways
- Know the doses used. The trial gave 200 mg CoQ10 and 200 µg selenium (as selenized yeast) daily. Those are study doses, not a recommendation.
- Check your selenium status first. If you are already replete, extra selenium is unlikely to help and may carry risk.
- Do not exceed 400 µg/day of selenium from all sources combined, including multivitamins, fortified foods and Brazil nuts, which can be very high in selenium.
- Talk to your doctor before starting, especially if you take blood thinners such as warfarin, since CoQ10 may interact with anticoagulant therapy. The same goes if you have heart disease or take other cardiac medications.
- Don't swap supplements for proven care. Blood pressure control, lipid management and exercise remain the foundation of cardiovascular prevention.
The Bottom Line
KiSel-10 is one of the more striking supplement trials in cardiology. Cardiovascular deaths fell from 12.6% to 5.9%, NT-proBNP dropped, and heart function scores improved, all in a randomized, double-blind setting. But it was a single, modest study in a selenium-poor population, and it cannot say which supplement did the work. Treat it as a strong lead rather than a verdict: worth discussing with your doctor, and worth testing in larger, independent trials.
