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The Role of Vitamin D in Boosting the Immune System

6 of 12 in Series: The Essentials of Vitamin D Benefits

Vitamin D may have a role in boosting the immune system and helping your body fight off nasty infections such as the flu and tuberculosis. Many books have been written about the positive effect of sunlight on these and other infectious diseases. These diseases are caused by viruses, bacteria, and other tiny organisms that enter the body through the lungs, the skin, or the intestines.

Managing tuberculosis with vitamin D

Some scientists think that vitamin D could play a major role in managing tuberculosis, a disease of the lungs. Tuberculosis (TB) is a common infection caused by the bacteria Mycobacterium tuberculosis in humans. About one-third of the world’s population has been infected with TB, but most infections don’t cause disease; they just remain quietly in the body.

Vaccinations may prevent tuberculosis, and TB is usually treated with antibiotics. This treatment approach has been effective, but tuberculosis continues to be a major problem. Antibiotic-resistant strains of the organism have developed and are difficult to treat. Also, immune diseases such as HIV/AIDS allow the disease-causing organism to spread throughout the body.

In 75 percent of patients, TB starts in the lungs. Other areas that are affected after spreading from the lungs include:

  • The pleura, the tissue that surrounds the lungs

  • The central nervous system, with tuberculous meningitis

  • The neck, with involvement of lymph nodes leading to a condition called scrofula

  • The genitourinary system, with involvement of the kidneys

  • The bones and joints, leading to Pott’s disease of the spine

Signs and symptoms of tuberculosis

Pulmonary tuberculosis involves the following symptoms:

  • Chest pain

  • Cough, often producing blood

  • Fatigue

  • Fever

  • Night sweats

  • Weight loss

Doctors can identify the disease by taking a sputum (stuff you cough up from your lungs) sample and examining it under a microscope. The presence of Mycobacterium tuberculosis, an organism that is bright-red and elongated, confirms the diagnosis.

The role of vitamin D and calcitriol in tuberculosis

The first suggestion that vitamin D might be beneficial for TB was from anecdotal reports from doctors and their patients in the days before antibiotics were available as a treatment. They swore that both sunlight and cod liver oil were cures for the disease.

Other people noticed that TB rates were higher in African Americans (45 percent of U.S.-born citizens who contract TB are black). What do these things have in common? Vitamin D! Unfortunately, these types of findings aren’t strong enough proof to stop doctors from using antibiotics and start using vitamin D supplements to treat TB.

People who have TB are more likely to have lower serum 25-hydroxyvitamin D levels than healthy people. The problem is we don’t know if this is the cause of the TB or an effect that results from the infection. Strong proof of principle that calcitriol protects against TB comes from cell studies.

There is much information that relates vitamin D to the chance of getting TB or the speed of recovery from the disease; however, to date, researchers haven’t figured out how to use this information. They haven’t determined the level of 25-hydroxyvitamin D needed to protect a person from tuberculosis, nor have they shown that increasing vitamin D intake with a vitamin D supplement will help a person recover from TB. For now it is still prudent to keep your serum 25-hydroxyvitamin D levels over the 20 ng/ml [50 nmol/L] level recommended for general health.

Fending off flu and viruses with vitamin D

New cell-based research from the last couple of years shows that calcitriol enhances innate immunity by prompting cells to produce a large numbers of antimicrobial peptides that are like broad spectrum antibiotics. These are substances that kill viruses, bacteria, and fungi — and they also modify the way other cells of the innate and adaptive immune system work. This may explain how calcitriol could protect you against the influenza virus.

So what’s the direct evidence that more vitamin D is good for preventing infections like the flu or other upper respiratory tract (URT) infections? The first line of evidence is that monocytes treated with calcitriol make antimicrobial peptides that kill viruses.

There are even a few clinical studies that support the idea that a supplement with vitamin D would reduce the number of URT infections or flu. The problem is that those studies aren’t big or weren’t done quite right, and none of them can define a vitamin D level for protection.

For example, a small study out of Japan in 2010 was widely covered in the media for its claim that vitamin D use in schoolchildren reduced the cases of influenza A. One problem with that study is that almost 25 percent of the subjects dropped out; whenever the dropouts exceed 5 to 10 percent, a study’s results become skewed and questionable. But more importantly, the number of cases of influenza B increased by almost the same amount that the cases of influenza A decreased.

So, the study actually showed no net change in influenza cases, and it was too small of a study to conclude anything with certainty. So, even though it looks like vitamin D may be useful for stopping infections, we need more proof for this relationship as well as more information about how much vitamin D is required to prevent the flu.

Make sure your blood level of vitamin D is above 20 ng/ml [50 nmol/L] before the winter flu season. At present there’s no proof that you need more than that. If you wait until you get the flu to start taking vitamin D, it might be too late.

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