Vitamin D levels and the risk of a recurrent heart attack: New research findings

The TARGET-D study, presented at the 2025 AHA Scientific Sessions, brings promising data for patients who have experienced a heart attack.

Targeted optimisation of vitamin D levels may help reduce the risk of a recurrent heart attack. Here, we explain what is already known while we await the full peer-reviewed publication.

Vitamin D has long been part of conversations around immunity, bone health, and overall well-being. Increasing evidence, however, suggests that its role extends far beyond these classical functions. One area that has attracted particular interest among researchers is the relationship between vitamin D levels and cardiovascular health.

The latest findings from the large TARGET-D clinical trial, conducted by Intermountain Health, shed new light on this topic, especially for individuals who have already experienced a heart attack. This is one of the first studies to focus not just on giving a standard supplement dose, but on achieving a specific, targeted vitamin D level in the body.

Why Does Vitamin D Matter for Heart Health?

Vitamin D is involved in numerous processes that are important for the cardiovascular system. It helps regulate inflammation, supports healthy endothelial function, and contributes to balance within the RAA system (renin–angiotensin–aldosterone), which plays a key role in blood pressure control. It also influences calcium metabolism and plays a part in glucose regulation and tissue insulin sensitivity. Increasing evidence suggests that optimal vitamin D levels may also correlate with better sleep quality and a more stable circadian rhythm, both of which affect cardiovascular wellbeing.

These mechanisms represent just part of the broader picture, showing why vitamin D is considered an important element in long-term support of heart and circulatory health.

How Did Vitamin D Deficiency Become So Common? Light and Modern Lifestyle

Just a few decades ago, most people synthesised a significant portion of their vitamin D through regular exposure to sunlight. Today, due to office-based work, spending most of the day indoors, concerns about skin cancer, and the common habit of using UV protection “just in case,” sunlight exposure has dropped dramatically.

It is estimated that half to two-thirds of the population now has vitamin D levels below the optimal range. In the TARGET-D study, as many as 85% of post–heart attack patients had levels below 40 ng/mL.

Why Didn’t Earlier Studies Show Clear Benefits?

Many people recall previous large clinical trials that did not confirm a reduction in cardiovascular risk from vitamin D supplementation. The key, however, lies in how those studies were designed.

Most earlier trials:

  • gave the same dose of vitamin D to every participant,
  • rarely measured baseline 25(OH)D levels before starting,
  • did not monitor whether the dose actually raised vitamin D levels,
  • did not adjust treatment to individual needs.

In other words, they focused on the dose, not on the biological outcome. GrassrootsHealth, an organisation that has gathered extensive long-term data on vitamin D, points out that supplementation often appears “ineffective” simply because the dose was too low to reach a clinically meaningful level. TARGET-D is one of the first studies to reverse this logic: Instead of giving the same dose to everyone, it measures, adjusts, and aims for a meaningful target level.

Czy poziom witaminy D może zmniejszyć ryzyko kolejnego zawału?

Target-to-Treat (“Treat-to-Target”, T2T) – a Modern Approach to Correcting Vitamin D Deficiency

The approach used in the TARGET-D study was based on a simple yet highly effective model:

  1. Measure the 25(OH)D level.
  2. Set a target (in the study: ≥40 ng/mL).
  3. Adjust the dose instead of giving the same amount to everyone.
  4. Monitor regularly until the target is reached.
  5. Once the goal is achieved, switch to annual follow-ups.

As a result, more than half of the patients required at least 5,000 IU of vitamin D per day, and many commonly recommended doses (600–800 IU) proved far too low. Only individualised treatment allowed participants to reach meaningful vitamin D levels and see real benefits.

What Exactly Did the TARGET-D Study Show?

Among patients whose vitamin D levels were actively monitored and adjusted to exceed 40 ng/mL, researchers observed about a 52% lower risk of a recurrent heart attack compared with the group whose vitamin D levels were not managed. This is a substantial and clinically meaningful difference.

It is important to note, however, that the overall MACE rate (heart attack, stroke, heart failure hospitalisation, or death) did not differ significantly between the groups. The most pronounced benefit was specifically seen in the reduction of recurrent heart attacks. This suggests that vitamin D optimisation may play a particularly important role in stabilising the condition of patients who have already experienced a heart attack.

Sunlight Beyond Supplementation: The Role of Light Exposure in Heart Health

Vitamin D is only one outcome of sunlight exposure. Sunlight influences the cardiovascular system in several additional ways, including:

  • Nitric oxide (NO) – UVA light releases NO from the skin, which helps lower blood pressure.
  • Regulation of the circadian rhythm affecting sleep and recovery.
  • Anti-inflammatory effects of red and near-infrared light.
  • Indirect effects on stress, which also impact cardiovascular health.

This is why we emphasise that sunlight is, first and foremost, a biological signal for the body – something far broader than a “vitamin D factory.” Light activates multiple pathways in the skin and nervous system that are relevant to heart function and overall wellbeing.

Vitamin D is an important response to light, but it is not the only one. The goal is not to replace sunlight with a supplement, but to understand light as a regulatory factor that influences a wide range of physiological processes.

What Does This Mean for People After a Heart Attack and for Healthy Individuals?

For patients after a heart attack:
  • It is important to know whether 25(OH)D levels are within a healthy range, as deficiency is particularly common in people with cardiovascular disease.
  • Targeted optimisation of vitamin D levels (as in the TARGET-D study) may be one component of care, but only under medical supervision and with regular monitoring.
  • Natural exposure to daylight remains valuable but should be adjusted to individual health status — especially if other conditions are present.
For healthy individuals:
  • Daylight and mindful sun exposure can support cardiovascular health not only through vitamin D, but also by influencing blood pressure, heart rhythm, sleep, and mood.
  • It is beneficial to maintain vitamin D within the optimal range (around 40–60 ng/mL), ideally through a combination of sunlight, lifestyle habits, and, when necessary, supplementation during low-light periods.
  • Balance is key: neither excessive tanning nor complete avoidance of sunlight supports long-term health.

Safety: What Do We Know?

The study reported no signs that individualised, higher doses of vitamin D₃ (such as 5,000 IU) pose a risk when used in a controlled and monitored manner. The concern is not the higher dose itself, but rather using supplementation without proper testing and follow-up.

Limitations, Next Steps, and What We Can Expect

The TARGET-D study offers very promising results, but so far we know it only from an abstract presented at the 2025 AHA Scientific Sessions. The full, peer-reviewed publication is currently in preparation.

It’s also important to remember that TARGET-D included individuals who had already experienced a heart attack — a high-risk group. The strongest effect was seen in reducing the risk of a recurrent heart attack. For other cardiovascular outcomes (such as stroke, heart failure, or mortality), larger and longer studies are needed to determine whether targeted vitamin D management brings similar benefits.

The research team has already announced the next phase of the project, involving a larger study population. This will help answer questions that the current data cannot yet resolve.

Until the full paper is published, these findings should be viewed as an encouraging direction worth following. Once the final study results become available, we will return to the topic on Sun for Life and explore their significance in the context of light exposure, lifestyle, and conscious cardiovascular care.

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