Can Vitamin D Deficiency Affect Autoimmune Diseases? Know What a Doctor and Studies Say

Vitamin D has long been recognised as an essential nutrient for maintaining healthy bones and supporting calcium absorption. However, research over the past few years has shown that its role extends far beyond bone health. Scientists now understand that vitamin D also plays an important part in regulating the immune system. This has raised interest in its possible connection with autoimmune diseases, where the body's immune system mistakenly attacks its own healthy tissues.

Can Vitamin D Deficiency Cause Autoimmune Conditions?

Although vitamin D deficiency alone does not cause autoimmune diseases, growing scientific evidence suggests that it may influence their development, progression, and severity, including a 2025 study published in the International Journal of Molecular Sciences. Maintaining healthy vitamin D levels is therefore considered an important part of overall health, particularly for people living with or at risk of autoimmune conditions.

According to Dr Tushar Tayal, Associate Director - Internal Medicine, CK Birla Hospital, Gurugram, “The function of vitamin D has been well known for many years because of its role in maintaining strong bones and calcium metabolism. However, there is now enough scientific evidence to show that its benefits go beyond bone health. Vitamin D plays a key role in regulating the immune system by maintaining a balance between activating immune responses and preventing the immune system from attacking the body's own healthy cells. When this balance is disturbed, it can affect the normal functioning of the immune system.”

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The Role of Vitamin D in Immune Health

According to a 2023 study published in the journal 'Experimental and Molecular Pathology', vitamin D supports the immune system by influencing the activity of immune cells. It helps the body respond appropriately to infections while preventing excessive immune reactions that may damage healthy tissues.

A healthy immune response depends on maintaining a careful balance. Vitamin D contributes to this balance by supporting immune regulation rather than simply increasing immune activity. This means it helps ensure that the immune system responds when needed but does not become overactive.

According to a 2025 systematic review published in the European Journal of Cardiovascular Medicine, researchers from different government hospitals in India believe that when vitamin D levels are too low, this balance may be affected, increasing the risk of abnormal immune responses in some individuals.

What does the studies indicate?

Over the years, several observational studies have explored the link between vitamin D deficiency and autoimmune diseases. Many of these studies have found that people with autoimmune conditions often have lower vitamin D levels than the general population.

Experts have also observed an inverse relationship between vitamin D levels and disease activity in certain autoimmune disorders. This means that lower vitamin D levels are sometimes associated with more active or severe disease.

However, these findings should be interpreted carefully.

Also Read: Can You Have More Than One Autoimmune Disease?

While the association is clear in many studies, it does not prove that vitamin D deficiency directly causes autoimmune diseases. Instead, it suggests that vitamin D deficiency may influence how these conditions develop or progress.

Dr Tayal explains, “Although low vitamin D levels do not indicate that vitamin D deficiency causes autoimmune diseases, they do show that vitamin D status may affect the development and course of these conditions.”

Genetics and Environmental Factors

According to a 2025 study published in the journal 'Frontiers in Immunology', autoimmune diseases develop due to a combination of genetic and environmental factors. Genetics remains one of the strongest risk factors, meaning people with a family history of autoimmune diseases may have a higher risk of developing them.

• However, environmental influences also play an important role. These include infections, smoking, stress, dietary habits, and vitamin D deficiency.
• Experts believe that these factors may trigger or worsen autoimmune diseases in people who are already genetically susceptible.
• Because vitamin D is produced in the skin after exposure to sunlight, people who spend little time outdoors, have darker skin, cover most of their skin, or live in areas with limited sunlight may be more likely to develop a deficiency.

Can Vitamin D Supplements Help Manage Autoimmune Conditions?

Vitamin D supplements are commonly recommended for people. Correcting a deficiency is important for bone health and may also support normal immune function.

Some clinical studies have examined whether vitamin D supplements can reduce autoimmune disease activity. While certain studies have shown promising results in selected patients, the evidence is still evolving. Researchers continue to study whether supplementation can help prevent autoimmune diseases or improve long-term outcomes.

Also Read: Can Stress Trigger Autoimmune Diseases? What Science Says

“Vitamin D supplements should not be considered a replacement for prescribed treatment. People with autoimmune diseases should continue following their doctor's advice regarding medication, diet, and regular follow-up. Any decision about taking supplements should be made after discussing it with a healthcare professional, as excessive vitamin D intake can also cause health problems,” highlights Dr Tayal.

Maintaining Healthy Vitamin D Levels

Maintaining adequate vitamin D levels is achievable. Here are some tips to boost vitamin D:

• Safe sunlight exposure is the ideal way to get vitamin D naturally.
• Consume a balanced diet.
• Foods such as oily fish, egg yolks, fortified dairy products, and fortified cereals provide some vitamin D.
• If your vitamin D levels are very low, consult a doctor and take supplements to elevate the levels.

When To See a Doctor

People who are at higher risk of deficiency may benefit from having their vitamin D levels checked through a blood test. If deficiency is confirmed, a doctor can recommend the appropriate dosage of supplements based on individual needs.

Final Word

Vitamin D is no longer viewed as a nutrient that only supports bone health. It is now recognised as an important regulator of the immune system, helping maintain the balance needed for normal immune function. Several studies suggests that people with autoimmune diseases often have lower vitamin D levels, and deficiency may be linked with increased disease activity in some conditions. Although vitamin D deficiency does not directly cause autoimmune diseases, it may influence their development and progression alongside genetic and other environmental factors.