Vitamin D deficiency increases the risk of stroke and associated kidney damage

Stroke remains the leading cause of death worldwide. Acute kidney injury is also a common complication that increases the risk of prolonged hospitalization and death. Previous studies have shown that vitamin D deficiency increases the risk of stroke, and it also appears that vitamin D deficiency raises the risk of acute kidney injury and early death following a stroke. This is highlighted in a new study published in Frontiers in Nutrition.

Each year, more than 12 million people worldwide suffer a stroke. The majority (62%) experience ischemic stroke, which occurs when a blood clot in the brain blocks a blood vessel. This cuts off the oxygen supply and damages the surrounding brain tissue. Symptoms occur suddenly and depend on which part of the brain is affected. It has also been shown that acute kidney injury is a common subsequent complication, occurring in 12-21 percent of patients. This results in a two- to three-fold higher risk of hospitalization. There is also an increased risk that the patient will die in the hospital or develop chronic kidney disease at a later stage, which significantly impairs their quality of life.
Because acute kidney injury following a stroke is such a serious condition, the researchers behind the new population-based study wanted to investigate whether widespread vitamin D deficiency is also associated with the risk of kidney failure and early death. The researchers obtained relevant data from TriNetX to identify more than 14,000 adult patients who had a first documented ischemic stroke between 2010 and 2024. The patients’ blood levels of vitamin D were recorded six weeks prior to their stroke, and the patients were then divided into two equal groups, each consisting of 4,343 individuals.
One group included patients with low vitamin D levels, while the control group included patients with sufficient levels (above 75 nmol/L). The groups were then compared over the following 12 months in terms of cases of subsequent acute kidney injury and other complications.
The study revealed that stroke patients with low levels of vitamin D in their blood had a significantly higher risk of developing acute kidney injury compared to stroke patients with sufficient vitamin D levels. Patients with vitamin D deficiency also had a higher overall mortality risk, as well as an increased risk of admission to intensive care, developing pneumonia, or requiring dialysis. The health risks associated with vitamin D deficiency persisted throughout the study’s 12-month follow-up period.
The researchers therefore conclude that vitamin D deficiency prior to a stroke is associated with an increased risk of subsequent acute kidney injury, other serious complications, and early death. It would therefore be relevant for stroke patients to have their vitamin D levels measured and to receive vitamin D supplementation as soon as possible, in doses sufficient to raise levels above 75 nmol/L.
At the same time, there should be greater focus on maintaining optimal blood levels of vitamin D in the prevention of stroke and many other diseases - year-round and throughout life.

How does vitamin D protect against stroke and complications?

Most of the body’s cells have receptors for vitamin D, which regulate a wide range of genes and metabolic processes. In the introduction to the study, the authors elaborate that vitamin D protects against stroke and acute kidney injury through several mechanisms, including:

• Maintaining endothelial cell function, including endothelial cells in blood vessels, the brain, and the kidneys
• Regulating the renin–angiotensin–aldosterone system (RAAS), which plays a role in blood pressure and fluid balance and is activated in the kidneys
• Counteracting chronic inflammation and oxidative stress, which contribute to atherosclerosis and many chronic diseases
• Protecting the kidneys by reducing excess protein (albumin) in the urine
• Counteracting fibrosis - the formation of scar/connective tissue
• Helping to prevent diabetes and related metabolic disturbances in the kidneys

Vulnerable groups should focus more on optimal vitamin D levels

It is well known that older adults, people who are overweight, individuals with diabetes, and many others with chronic diseases have an increased risk of stroke. It is also known that vitamin D deficiency is more prevalent among these vulnerable groups. Official recommendations for vitamin D intake range from 5–20 micrograms daily, with higher doses recommended for those over the age of 70. However, many people do not get sufficient summer sun exposure or take the recommended supplements. Furthermore, the official recommendations are not guaranteed to optimize blood levels of the nutrient.
Therefore, it is safer to have blood levels of vitamin D measured and to take appropriate supplements if a deficiency is present. That way, individuals are better protected against stroke, complications, and many other diseases.

References:

Kuo-Chuan Hung et al. Vitamin D deficiency and risk of acute kidney injury after ischemic stroke: a propensity-matched cohort study. Frontiers in nutrition. 2026

Intermountain Healthcare. Vitamin D3 breakthrough halves risk of second heart attack. ScienceDaily. November 10, 2025