Does vitamin D help after a heart attack? What the TARGET-D trial found

Low vitamin D is common in people with heart disease, and observational studies have long linked low levels to worse outcomes. That made vitamin D an appealing candidate for preventing further heart problems after a heart attack. Large trials have mostly disappointed, and some researchers have argued that is because they gave everyone the same modest dose.

The TARGET-D trial, published in the European Heart Journal, tried a different approach: measure each patient’s vitamin D and adjust the dose until they reach a target level. It did not clearly reduce the main combination of heart events, although one secondary result has drawn attention.

Why vitamin D and the heart have been linked

MedlinePlus explains that vitamin D is important because it helps your body absorb calcium, and that it also plays roles in muscles, nerves and the immune system. People with low blood levels tend to have more heart disease, but that link could reflect age, weight, illness or less time outdoors rather than the vitamin itself.

The trial’s authors summarize the problem: many observational studies have reported associations between low serum 25-hydroxyvitamin D levels and adverse cardiovascular outcomes, but randomized trials have not shown fewer heart events with supplements. They suggested those trials may have fallen short because of fixed or non-targeted dosing.

What earlier vitamin D trials found

Two large trials set the backdrop. VITAL, in 25,871 adults in the US, tested 2,000 units of vitamin D a day. Supplementation with vitamin D was not associated with a lower risk of either of the primary end points, which included major cardiovascular events, over about five years.

D-Health, in 21,315 older Australians, tested a large monthly dose for up to five years. The rate of major cardiovascular events was lower in the vitamin D group than in the placebo group, 6.0% against 6.6%, but the difference was small and could not be clearly separated from chance. The gap looked a little larger among people already taking heart medicines, a pattern that was also not statistically clear.

How the TARGET-D trial worked

TARGET-D enrolled people who had recently had a heart attack. MedlinePlus explains that a heart attack happens when blood flow to the heart suddenly becomes blocked, damaging heart muscle. Participants were randomly assigned to usual care or to vitamin D3 with a dosing algorithm to reach and maintain a target 25(OH)D level of >40-80 ng/mL, a blood measure of vitamin D in nanograms per milliliter.

Most started low. The median level at the start was 25 ng/mL, 87% were at 40 or below, and 52.4% began vitamin D3 dosing at 5000 IU, a high dose. The comparison group received usual care rather than a placebo, and patients were followed for an average of about four years.

What happened to heart events with targeted vitamin D

The main outcome combined death, heart attack, heart failure hospital admission and stroke. Major adverse CV events did not achieve significance, meaning the difference between groups was too small to rule out chance: 15.7% with vitamin D against 18.4% with usual care.

Among the separate outcomes, repeat heart attacks were less common with vitamin D, 3.8% against 7.9%. Deaths were almost the same, heart failure admissions and strokes slightly more common with vitamin D, and all of those differences were small. The authors conclude that targeted vitamin D supplementation and ongoing titration did not significantly reduce major adverse CV events.

Why the repeat heart attack result is uncertain

A secondary result can be a genuine clue or a statistical accident. It is one of several outcomes the trial looked at, based on small numbers of events, and it sits alongside no difference in deaths and slightly more strokes and heart failure admissions. Checking many outcomes raises the chance that one of them looks significant by luck.

The honest reading is that TARGET-D raises a question worth testing in a larger trial designed around repeat heart attacks. It does not show that vitamin D prevents them.

What the TARGET-D trial cannot tell us

With 630 patients, the trial was too small to detect modest effects reliably. It was pragmatic and compared vitamin D with usual care rather than a placebo, so patients and doctors knew who was being treated, and most participants were men.

The doses were high and closely managed by the research team, which is different from people choosing supplements themselves. Very high vitamin D levels can raise blood calcium, which is one reason the trial adjusted doses using repeated blood tests rather than giving a fixed high dose.

What the vitamin D evidence adds up to

Across VITAL, D-Health and now TARGET-D, vitamin D has not clearly reduced major heart events, whether given at a fixed daily dose, a monthly dose, or a dose tailored to blood levels after a heart attack. The hint of fewer repeat heart attacks in TARGET-D is interesting but unconfirmed.

Care after a heart attack rests on treatments with proven effects, which a cardiology team tailors to each patient. MedlinePlus notes that quick treatment can limit damage during a heart attack and that calling 911 gets you care faster than making your own way to hospital.