How Low Vitamin D Levels Impair Your Immune Health

8 October 2020

Do you know low vitamin D levels could be the reason you get frequent colds and flu? While the sunshine vitamin’s role on bone health has been well established, researchers are increasingly interested in its effects on your immune health.

Emerging evidence suggests that adequate levels are critical to helping your body fight off bacterial and viral infections.

Vitamin D and Respiratory Infections: What Science Says

Many large studies have shown that people with respiratory infections like colds, bronchitis, and pneumonia often have insufficient vitamin D levels.

Notably, the role of vitamin D in tuberculosis (TB) has attracted wide attention in recent years. Before the availability of antitubercular drugs, doctors used the vitamin to treat TB. Currently, scientists are studying if it could be used to prevent or limit TB. TB patients have low levels of the vitamin and supplementation is shown to accelerate recovery. (1)

Elite athletes often use vitamin D supplements to reduce their risk of getting a respiratory infection. According to a 2015 study, (2)

University athletes who took vitamin D3 each day for 14 weeks had:

● Significantly higher levels of antimicrobial chemicals in their saliva
● Improved protection against respiratory infections

Vitamin D Deficiency is More Common in the UK than You Think

About 20% of adults in the UK have low levels of the vitamin, according to the National Diet and Nutrition Survey (NDNS). Likewise, the NHS reports 16% of children are deficient. (3,4) Various factors are responsible for the rising incidences of deficiency. These include:

● Diet
● Lifestyle factors, including smoking
● Weather
● Northern latitude in the UK
● Obesity

Obesity is a well-established cause of vitamin D deficiency, suggests a 2013 study. (5) The study, which involved over 42,000 participants, found that:

For every 10% increase in the body mass index (BMI), there will be a 4.2% decrease in 25(OH)D concentrations. 25(OH)D is a product of vitamin D3 metabolism in the liver. Blood tests measure the levels of 25(OH)D to predict the amount of vitamin D in the body.

Vitamin D and Immunity: The Lesser-Known Yet Intriguing Link

Vitamin D affects two types of immunity – innate and adaptive immunity.

Innate immunity provides non-specific protection against invading microbes (antigens). For example, the skin acts as a barrier to prevent the entry of bacteria and viruses into the body.

Adaptive immunity helps get rid of microbes by producing specialised proteins called antibodies. This type of immunity develops as you grow.

Vitamin D has a powerful antibacterial activity. It enhances the production of antibacterial chemicals, most notably, cathelicidin and beta defensin 4. (6)

Vitamin D Has Unique Immunomodulatory Effects

It not only protects you against infections but can also help reduce the severity of autoimmune disorders. Autoimmune disorders occur when your immune system attacks healthy cells and tissues in the body.

Common examples include type 1 diabetes, Crohn’s disease, rheumatoid arthritis (RA), and multiple sclerosis (MS). Researchers have noted that low vitamin D levels are common in people with autoimmune disorders.

Vitamin D Supplementation for Enhanced Immunity: Things to Know

Doctors recommend daily and weekly supplementation to keep your immune system competent, especially during the cold season.

Most notably, daily or weekly supplementation is usually more effective than large single doses. The NHS recommends people take 10 micrograms per day to support bones and muscles, however for immune health there is discussion that larger quantities are beneficial.

Both Cartonica for joint health and Vitaliti for wellbeing contain more than 10micrograms per serving, along with a host of other nutrients.

Nutrients and supplements where needed are one part of the equation for a healthy life. More important are to stay active, eat healthy, get quality sleep, drink plenty of water, limit alcohol.


  1. Journal of Clinical and Translational Endocrinology. Vitamin D status, receptor gene polymorphisms, and supplementation on tuberculosis: A systematic review of case-control studies and randomized controlled trials*.
  2. Journal of Sports Sciences.The effect of 14 weeks of vitamin D3 supplementation on antimicrobial peptides and proteins in athletes.
  3. Public Health England. National Diet and Nutrition Survey.
  4. NHS Nottingham University Hospitals. Vitamin D deficiency in children.
  5. PLoS Medicine. Causal Relationship between Obesity and Vitamin D Status: Bi-Directional Mendelian Randomization Analysis of Multiple Cohorts.
  6. UCLA Health. Non-Classical Effects of Vit D.