Targeted vitamin D3 supplementation cuts risk of second heart attack in half, study finds

Medical Xpress / Intermountain Healthcare / ^ | Nov. 9, 2025

[ConservativeMind]

A tailored approach of vitamin D3 supplementation in patients who have suffered a heart attack significantly reduces their risk of a second heart attack, a new study finds.

In a large, randomized clinical trial, researchers found that treating heart attack patients in a "target to treat" fashion, where patients' blood levels of vitamin D were monitored and vitamin D3 dosing adjusted to achieve optimal levels, cut their risk of a second heart attack in half.

The study, called the TARGET-D trial, enrolled patients from April 2017 to May 2023 and included 630 patients who had a heart attack within a month of their enrollment. Participants were followed until March 2025 for the occurrence of cardiovascular events.

Researchers randomized study patients into two groups: those who received no management of vitamin D3 by the study and those who received targeted vitamin D3 treatment.

In the vitamin D treatment group, the goal was to raise their blood levels of vitamin D to more than 40 nanograms per ml (ng/mL). Of the heart attack patients enrolled in the study, 85% had insufficient vitamin D3 levels (<40 ng/mL).

Of those who received targeted treatment, more than 50% required an initial vitamin D3 dose of 5,000 international units (IU), where current supplementation suggestions are usually between 600 to 800 IU.

For patients in the study who received targeted treatment, their vitamin D blood levels were checked once a year to determine if they were above 40 ng/mL. For patients whose vitamin D levels were lower, they were tested every three months with their dosage adjusted, then every year after they achieved 40 ng/mL.

Intermountain researchers then followed patients to see who had follow-up major cardiac events (MACE), including heart attack, heart failure hospitalization, stroke or death.

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TOPICS: Health/Medicine
KEYWORDS: cardiac; d3; heart

[ConservativeMind]

At 40 ng/mL of vitamin D in the blood, all cardiac events were cut in half.

85% of people with cardiac events had less than that, prior to receiving the vitamin D in this study.

Yes, you should know if you have adequate vitamin D, even if only checked one time, unless you can surmise you already get enough.

[ConservativeMind]

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[for-q-clinton]

What about D2?

[decal]

Or WD-40?

[KittyKares]

D3 was even important in keeping one from getting a bad case of Covid, as I recall. I’m finding that Vitamin D is important for more aspects of health than I realized, especially since the levels seem to decline in old age.

[ConservativeMind]

Nearly everything I read says it’s best to only take vitamin D3.

[ConservativeMind]

My one vitamin D test showed I had 36 ng/mL.

I would be a little low, on this concern.

[for-q-clinton]

I looked it up and yes “best” for D3, but D2 works but D3 is just a bit better. D2 is for vegans who don’t want anything from animals.

[The Duke]

As I understand it, D2 gets turned into D3 in the body, however taking D3 directly ends up being more cost-effective.

[Uncle Miltie]

“40 nanograms per ml (ng/mL)”

Checking in at 63 myself. Two Costco sized gelcaps per day, one each in the morning and evening.

[catnipman]

“What about D2?”

vitamin D1 is actually the active form: D3 is converted to D2 in the body and then D2 is converted into D1 under control of the parathyroid gland because too much D1 is deadly, which is why it’s difficult to OD on D3 for those with a normally functioning parathyroid gland ...

[sauropod]

Been taking D3 for years.

[Red Badger]

I take 5000+ IUs every day...........

[JohnnyP]

Mine was in the low ‘90’s one year. The PA said that’s too high, and to back off on the capsules.

I was taking 20,000 IU’s a day. :)

[MomwithHope]

5000 in the winter, 1000 in the summer.

[Uncle Miltie]

Grok: “ Understanding Vitamin D Levels Vitamin D status is assessed by measuring serum 25-hydroxyvitamin D [25(OH)D] levels in the bloodstream, typically in nanograms per milliliter (ng/mL) or nanomoles per liter (nmol/L; 1 ng/mL ≈ 2.5 nmol/L). The “optimal” level refers to the concentration associated with the best health outcomes, including bone health, fracture prevention, immune function, and reduced risk of chronic diseases like cancer, cardiovascular issues, and diabetes. However, definitions vary due to differences in study populations, endpoints, and guidelines. Scientific consensus distinguishes: • Deficiency: <20 ng/mL (<50 nmol/L) – Linked to rickets, osteomalacia, secondary hyperparathyroidism, and increased fracture risk. • Insufficiency: 20–29 ng/mL (50–72.5 nmol/L) – May still pose risks for falls, bone loss, and suboptimal immune response. • Sufficiency/Optimal: ≥30 ng/mL (≥75 nmol/L) – Generally recommended for full health benefits. • Upper Limit: Levels >100–150 ng/mL (>250–375 nmol/L) risk toxicity (e.g., hypercalcemia), though sun exposure rarely causes this.”