Story at-a-glance

• A new Intermountain Health study presented at the American Heart Association's 2025 Scientific Sessions found that adults with heart disease who optimized their vitamin D levels cut their risk of another heart attack by 52%

• Most participants began the trial with low vitamin D levels, showing that deficiency is common in people with cardiovascular disease and silently increases the risk of recurring heart problems

• More than half of the patients needed over 5,000 IU of vitamin D3 daily — six times the FDA's recommended intake — to reach protective blood levels between 40 and 80 ng/mL

• Vitamin D acts as a hormone that helps lower inflammation, maintain proper calcium balance, improve blood vessel function, and reduce oxidative stress — all key to preventing heart damage

• Regular testing, personalized dosing, sunlight exposure, and daily exercise are simple, measurable ways to restore vitamin D, strengthen your heart, and reduce your risk of another cardiac event

Heart disease remains the leading cause of death worldwide,1 and one hidden factor keeps showing up in those most at risk — vitamin D deficiency. Low vitamin D doesn't just weaken your bones; it undermines the electrical and metabolic stability of your heart. This nutrient behaves more like a hormone than a vitamin, regulating hundreds of cellular functions that keep your cardiovascular system running smoothly.

When your vitamin D levels drop too low, calcium control falters, inflammation accelerates, and your heart's ability to generate energy declines. Over time, that imbalance contributes to high blood pressure, arterial stiffness, and mitochondrial dysfunction — conditions that silently wear down your body's most vital muscle.

Research presented by Intermountain Health at the American Heart Association's Scientific Sessions 2025 in New Orleans highlights how closely your vitamin D status tracks with your heart's strength and stability.2

The findings underscore a clear message: it's not enough to get some vitamin D — you need to reach and maintain the right level for your body. Understanding how personalized vitamin D optimization strengthens your heart reveals a powerful opportunity: you can directly influence an important variable in your long-term cardiovascular health.

Personalized Vitamin D Dosing Cut Repeat Heart Attack Risk by Half

The study, called TARGET-D, involved 630 adults with existing heart disease who had already experienced a major cardiac event such as a heart attack. It asked a simple but important question: if people with heart disease received personalized vitamin D doses to reach optimal blood levels, would that reduce their odds of another attack?

•Most participants started out severely low in vitamin D — When the study began, 85% of participants had blood levels below 40 nanograms per milliliter (ng/mL). That number is well under what many experts consider optimal for overall and cardiovascular health. The trial divided participants into two groups. One group continued with standard medical care — no monitoring or adjustment of vitamin D.

The other group had their levels checked and doses adjusted every few months until they reached the target range of 40 to 80 ng/mL. In most medical literature, vitamin D deficiency is defined as a blood level below 20 ng/mL, or about 50 nanomoles per liter (nmol/L). Levels between 20 and 30 ng/mL (50 to 75 nmol/L) are considered insufficient — meaning your body still isn't getting what it needs to function properly.

In my view, those ranges are far too low for optimal health, especially when it comes to cardiovascular protection. I recommend aiming for 60 to 80 ng/mL (150 to 200 nmol/L). That's the range where your heart, brain, and immune system perform best, and where your risk of chronic disease starts to drop.

•Those who achieved the target range were far less likely to suffer another heart attack — Over an average follow-up of 4.2 years, the treatment group — those whose vitamin D was optimized — had a 52% lower risk of another heart attack compared with those in the unmonitored group.

This is a powerful result, considering both groups had similar health histories at the start. It suggests that maintaining vitamin D at optimal levels is among the simplest and most measurable ways to reduce the chance of a repeat cardiac event.

•The doses required were higher than many people think — Nearly 52% of participants in the treatment group needed more than 5,000 international units (IU) of vitamin D3 per day to reach and maintain blood levels above 40 ng/mL. That's more than six times the 800 IU daily value recommended by the U.S. Food and Drug Administration.

The researchers adjusted doses every three months until participants stabilized in the desired range. This finding highlights how widely individual needs vary and why a single "recommended daily allowance" is often inadequate for restoring optimal vitamin D status, especially in adults with heart disease.

•The study design emphasized continuous management, not a one-time fix — Every participant in the targeted-dosing group received ongoing care throughout the four-year trial. Vitamin D levels were checked quarterly until stable, then annually. If levels dipped below 40 ng/mL again, doses were readjusted. This approach differs sharply from earlier vitamin D trials that gave everyone the same dose without testing blood levels first.

In this study, the focus was on reaching a therapeutic range, not handing out a universal dose. The data suggest that identifying vitamin D deficiency and adjusting dosage until blood levels reach 40 to 80 ng/mL could dramatically reduce the likelihood of another heart attack in those already living with heart disease.

The researchers encouraged patients to discuss testing and individualized supplementation with their doctors, emphasizing that targeted dosing based on blood results — not blanket dosing — is what made the difference.

Vitamin D Protects and Repairs Your Cardiovascular System

Vitamin D is technically a steroid hormone, not just a nutrient, and it plays a central role in reducing oxidative stress throughout your vascular system. Oxidative stress occurs when unstable molecules called free radicals damage your blood vessel walls, triggering inflammation that contributes to plaque buildup and heart disease. By lowering that oxidative load, vitamin D supports smoother blood flow and healthier vessel function — key factors in keeping your heart strong.

•The link between vitamin D and cardiovascular disease risk is now supported by multiple types of evidence — The overall body of research increasingly shows that vitamin D plays a significant role in reducing cardiovascular disease (CVD) risk.3

Observational studies consistently find that low blood concentrations of vitamin D — below 16 to 20 ng/mL (40 to 50 nmol/L) — are linked to the highest rates of heart attacks and cardiovascular deaths. A large prospective study showed an inverse relationship between vitamin D levels and CVD mortality up to 40 ng/mL (100 nmol/L), meaning that as vitamin D levels rose, heart-related deaths dropped.

•Vitamin D influences blood vessel structure and function — According to Norwegian researchers, vitamin D helps regulate several processes that determine how your arteries age and respond to stress.4 It affects endothelial function (the ability of your blood vessels to expand and contract), fibrosis (the stiffening of tissue from chronic inflammation), and plaque stability, all of which play key roles in the progression of coronary artery disease.

By keeping these systems in check, vitamin D helps maintain the flexibility and integrity of your arteries, reducing the likelihood of blockages or ruptures that lead to heart attack.

•Calcium balance links vitamin D to cardiovascular safety — One of vitamin D's main jobs is to maintain proper calcium levels in your blood. When calcium runs too high, it builds up inside your arteries and contributes to coronary artery disease. Genetically elevated serum calcium levels are linked to greater risk for heart attack.5

Vitamin D helps keep calcium in a safe range, lowering the threshold for how much calcium your body can safely handle and helping prevent hardening of the arteries.

•Vitamin D supports nitric oxide production, improving circulation and preventing clots — Other research shows that vitamin D3 stimulates your endothelium — the thin lining inside your arteries — to produce nitric oxide, a molecule that keeps blood vessels relaxed and open.6

Nitric oxide also acts as a signaling compound that helps prevent unwanted clot formation and ensures blood flows efficiently to your heart and brain. This means adequate vitamin D levels support not just stronger arteries, but also better overall circulation and lower risk of stroke or thrombosis.

How to Restore Vitamin D and Protect Your Heart from Another Attack

When you've already lived through one heart attack, every decision you make for your health matters more than ever. The good news is that vitamin D offers one of the most direct, measurable ways to rebuild resilience. This isn't about chasing perfection — it's about giving your body the sunlight, nutrients, and daily habits it needs to recover at the cellular level. If your goal is to lower inflammation, restore energy, and protect your heart, these are five effective steps to take right now.

1.Get your vitamin D from the sun whenever possible — Your skin is designed to make vitamin D3 when exposed to natural light. Aim for regular exposure on large areas of skin — like your arms, torso, and legs — without sunscreen. Watch for the first sign of pinkness as your natural "sunburn test." That's your body telling you you've had enough for that day.

Sunlight also powers up nitric oxide, which helps lower blood pressure and improves blood flow, while setting your circadian rhythm for better sleep and energy. Treat this like a daily recharge ritual — regular sunlight exposure makes a measurable difference in how your heart functions.

2.Cut out seed oils for heart health — and before spending time in strong sunlight — If you're still cooking with vegetable oils such as soybean, canola, sunflower, or safflower, your skin and heart are working against hidden damage. These oils flood your cells with linoleic acid (LA), a polyunsaturated fat that oxidizes when hit by ultraviolet rays, making you burn faster, especially during peak sun hours of 10 a.m. to 4 p.m., and age quicker.

LA also drives inflammation and damages mitochondrial membranes, the energy centers inside your cells, which directly impairs heart function over time.

Replacing these oils with stable fats like tallow, ghee, or grass fed butter supports your skin's natural defenses, restores mitochondrial health, and helps your body handle sunlight safely. Avoiding seed oils for at least six months gives your skin time to shed stored LA, helping you tolerate midday sun safely and produce vitamin D naturally again.

3.If you supplement, use vitamin D3 — not D2 — and always pair it with magnesium and vitamin K2 — When sunlight isn't an option, D3 is the only form worth taking. It's identical to the vitamin your skin makes and far more effective than D2.

I always recommend taking it alongside magnesium and vitamin K2, because they work as a team: magnesium activates vitamin D, and K2 makes sure the calcium it mobilizes ends up in your bones, not your arteries. Without these cofactors, you'd need twice as much D3 to get the same result.7 Taking the trio together improves absorption, protects your arteries, and supports heart muscle strength.

4.Test your vitamin D levels twice a year and track your progress — Guesswork isn't enough. You need to see the numbers. Test your vitamin D levels every six months, and aim for a range between 60 and 80 ng/mL (150 to 200 nmol/L). If your levels are lower, adjust your daily sunlight or D3 dose accordingly. This simple test gives you proof that your efforts are working and builds momentum to stay consistent. If your levels drop, you'll know before your heart feels the consequences.

5.Use exercise to keep vitamin D active and strengthen your heart year-round — When sunlight fades, movement takes over. Regular exercise keeps your vitamin D active by stimulating the enzymes that convert it into its usable form, while also directly improving your heart's strength, circulation, and efficiency. In one 10-week study, overweight adults who exercised regularly maintained better vitamin D function even with limited sun exposure.8

Whether you prefer brisk walks, resistance bands, or a short strength session, what matters is consistency. Exercise trains your heart to pump more efficiently, strengthens your arteries, and reduces inflammation — the same biological pathways that vitamin D supports.

Your heart needs energy, sunlight, and balance at the cellular level. These steps work together to give it exactly that. When you correct the underlying vitamin D deficiency, you don't just lower your risk of another heart attack — you build a stronger, more resilient foundation for every system in your body.

FAQs About Vitamin D for Your Heart

Q: How does vitamin D affect heart health?

A: Vitamin D acts more like a hormone than a vitamin, influencing hundreds of biological processes that support cardiovascular function. It helps regulate calcium balance, reduce oxidative stress, lower inflammation, and improve blood vessel flexibility. Adequate vitamin D levels also help produce nitric oxide, which relaxes blood vessels and supports healthy circulation. Together, these effects help protect your arteries, stabilize plaque, and reduce your risk of heart disease and stroke.

Q: What did the Intermountain Health study find about vitamin D and heart attacks?

A: The TARGET-D clinical trial, presented at the American Heart Association's 2025 Scientific Sessions, followed 630 adults with heart disease for more than four years.9 Those who maintained vitamin D levels between 40 and 80 ng/mL (100 to 200 nmol/L) through personalized dosing were 52% less likely to have another heart attack than those who received standard care.

This shows that individualized, monitored vitamin D optimization offers measurable protection for people already living with heart disease.

Q: What vitamin D levels are considered optimal for heart protection?

A: Deficiency is defined as below 20 ng/mL (50 nmol/L), and insufficiency falls between 20 and 30 ng/mL (50 to 75 nmol/L). I recommend aiming higher — ideally between 60 and 80 ng/mL (150 to 200 nmol/L) — to support heart, brain, and immune function. In the Intermountain trial, participants needed ongoing dose adjustments to stay in the protective range, with more than half requiring over 5,000 IU daily to reach it.

Q: Is there other research linking vitamin D to cardiovascular health?

A: Yes. Large observational studies show that low vitamin D levels — below 16 to 20 ng/mL (40 to 50 nmol/L) — correlate with the highest rates of heart attack and cardiovascular death. Supplementation trials also show modest reductions in cardiovascular risk factors such as high blood pressure and ischemic heart disease, especially when baseline vitamin D levels are low.

Q: What are the best ways to restore and maintain healthy vitamin D levels?

A: Get regular sun exposure on bare skin. To protect your skin from burning, eliminate seed oils high in LA for at least six months before getting midday sun exposure. If you use supplements, choose vitamin D3, not D2, and pair it with magnesium and vitamin K2 to maximize absorption and protect your arteries.

Test your vitamin D levels twice yearly, adjust your intake to stay between 60 and 80 ng/mL, and keep your heart strong through daily movement, avoiding seed oils, and nutrient balance year-round.