Narrowing of the carotid artery may be caused by vitamin D deficiency

The carotid artery supplies the brain with blood, and narrowing can lead to debilitating and life-threatening strokes. According to a study on middle-aged participants with high blood pressure, a deficiency in vitamin D increases the risk of calcification and narrowing of the carotid artery.

Narrowing of the carotid artery (arteria carotis) is caused by atherosclerosis, which increases the risk of blood clots that can travel with the blood to the brain. Symptoms depend on where the blood clot settles in the brain. If you have atherosclerosis in the carotid artery, there is also a significant risk of having atherosclerosis in the heart, legs, or other areas. Atherosclerosis, often associated with high blood pressure, is the leading cause of death in the Western world.
It is well known that diet and lifestyle have a significant impact on the development of atherosclerosis and high blood pressure. It is also known that low levels of vitamin D in the blood are associated with arterial stiffness and high blood pressure.
The aim of the new study was therefore to investigate whether blood levels of vitamin D are associated with subclinical narrowing of the carotid artery in patients with high blood pressure. The study included a total of 223 participants who had high blood pressure but no signs of diabetes or other cardiovascular or kidney diseases.
The participants' blood levels of vitamin D and parathyroid hormone (PTH), which plays a key role in calcium balance, were measured. Additionally, the researchers measured stiffness and degree of atherosclerosis in the carotid artery.
The participants were divided into three groups, depending on whether their blood vitamin D levels were normal, insufficient, or deficient. It was found that 59% of the participants had some degree of vitamin D deficiency. It was also found that low vitamin D levels in the blood were significantly associated with:

• Older age
• Long-term hypertension
• Higher fasting blood sugar and insulin levels, which occur in the prediabetic stage of type-2 diabetes
• Higher PTH levels
• Advanced development of atherosclerosis in the carotid artery
• Advanced development of arterial stiffness in the carotid artery

The researchers therefore conclude that vitamin D deficiency increases the risk of subclinical narrowing of the carotid artery in middle-aged patients with high blood pressure who are predisposed to more severe cardiovascular diseases. The new study is published in Nutrients and is consistent with previous studies showing that vitamin D has several positive effects on the cardiovascular system.

How does atherosclerosis develop – and how does vitamin D protect?

The often-demonized cholesterol is a vital substance involved in cell membranes, nerve cell extensions (myelin), as well as the formation of vitamin D, steroid hormones, and stress hormones. The liver normally produces most of the cholesterol that is needed by the body.
Cholesterol appears to become harmful to health when it is exposed to oxidative stress. This is a condition where potentially harmful free radicals outnumber the protective antioxidants . We all form free radicals during various metabolic processes, and their amount increases significantly due to smoking, aging processes, poisoning, and chronic diseases, which are often characterized by chronic inflammation.
In oxidative stress, free radicals can become unregulated and attack cholesterol, causing it to oxidize (become rancid) and lose its ability to perform its many functions. Instead, the oxidized cholesterol is consumed by certain white blood cells, which then become embedded in the blood vessel walls as foam cells. Subsequently, a calcium grid is formed as part of the development of atherosclerosis, which also leads to arterial stiffness.
It appears that vitamin D counteracts oxidative stress by regulating chronic inflammation, which occurs in aging, high blood pressure, and other chronic diseases. Vitamin D can also regulate blood vessel contraction through a system called RAS (renin-angiotensin-aldosterone). Additionally, vitamin D helps regulate insulin levels and blood sugar levels, which is good, as high levels are known to increase the risk of insulin resistance, high blood pressure, and other prediabetic conditions.
This protective effect requires that blood levels of vitamin D are optimal and above 75 nmol per liter.

References:

Luca Bulfone et al. Subclinical Carotid Disease Is Associated with Low Serum Vitamin D in Nondiabetic Middle-Aged Hypertensive Patients. Nutrients 2025

Anas Raed et al. Dose responses of vitamin D3 supplementation on arterial stiffness in overweight African Americans: A placebo controlled randomized trial. PLOS ONE, 2017