Vitamin D levels before infection may be related to risk of tuberculosis conversions, says new study

Posted on: October 12, 2014   by  Jeff Nicklas

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The history of the research linking vitamin D and tuberculosis extends back to the days well before antibiotics. In a case report from 1651, scientists found enlarged lymph nodes, which is often caused by tuberculosis, in a child suffering from vitamin D deficiency rickets.

Two hundred years later, in the mid-19th century, heliotherapy (sunlight) became a common and effective means to help improve clinical outcomes of tuberculosis.

While sun exposure initiates the production of vitamin D, it wasn’t until the middle of the 20th century that vitamin D was being considered as an effective therapy in patients with tuberculosis.

Since then, researchers have been increasingly interested in vitamin D’s role in the various aspects of tuberculosis. Vitamin D has been shown to enhance the innate immune system response, which is the part of the immune system that helps defend against infection, and it has been shown to help patients recover faster from tuberculosis and help with associated complications, such as improved breathing.

A new prospective study was recently conducted in which researchers looked at vitamin D levels and their relationship to tuberculosis infection conversion (TBIC) in latent tuberculosis 8-10 weeks after vitamin D measurements.

When a person becomes infected with tuberculosis (TB), it doesn’t mean that they will get sick or display symptoms. When someone contracts the TB bacteria, the bacteria can remain dormant, or what is termed latent. In latent TB, if a person’s immune system is strong enough they are be able to fight off the infection. If they can’t, TB can become active, and then the person does become sick.

For this study, researchers out of Spain recruited 198 participants from two different health departments. The participants had visited the health departments for tuberculosis screening because they were identified as having recent contact with a TB patient.

The researchers measured vitamin D levels at baseline and gave each participant a tuberculin skin test (TST) and a QuantiFERON-TB Gold In-Tube test (QFT-GIT).

The TST is the standard screening tool used to identify infection from the TB bacteria. It involves an injection of a protein derivative which causes a slight elevation of the skin where the injection occurred. A person is considered to have a positive test, and therefore infected with the bacteria, depending on the size of the elevation and their medical history.

QFT-GIT is an assay which collects a full tube of blood and measures a person’s immune response to the TB bacteria. The test quantifies the number of T-cells responding to the TB bacteria. A higher number of cells indicates that the bacteria is present. QFT-GIT is more accurate than the TST and is considered the preferred method of screening.

By using both methods in this study, the researchers were able to get a highly accurate understanding of whether or not the participant became infected and underwent TBIC.

These two tests were administered at the same time as the vitamin D measurement and again 8-12 weeks later. Measurements of vitamin D were only conducted once at baseline.

The researchers were interested in whether vitamin D levels in participants not infected with the TB bacteria related to the risk of developing latent TB at the end of the study.

Here’s what they found:

  • Average vitamin D levels in those who had TBIC cases was 20.7 ng/ml compared to 27.2 ng/ml among those who did not develop latent TB.
  • Risk of TB was significantly less in those with vitamin D levels greater than 20 ng/ml (P = 0.012).
  • A vitamin D level of 20 ng/ml or higher was related to an 85% decreased incidence of TBIC (P = 0.005).
  • Every 1 ng/ml increase in vitamin D was significantly associated with a 6% decrease in the incidence of TBIC (P = 0.015).

The researchers stated,

“The results of the study indicate that vitamin D status was associated with TBIC in contact of pulmonary TB patients. Deficient and very deficient vitamin D status was associated with high TBIC.”

In acknowledging both the strength of their results and the observational design of the study, they went on to add,

“Therefore, if the association were causal, one out of two TBIC occurring in participants with less than 20 ng/ml vitamin D may be attributable to vitamin D deficiency.”

The observational design of the study means we cannot say for certain that any causal relationship exists. Furthermore, the measurement of only baseline vitamin D levels limits the results. Without further measurements, it is hard to know if any changes occurred in vitamin D status and what those changes might mean in the development of latent TB.

As with other prospective studies, randomized controlled trials are need to confirm these findings. Trials have been conducted, such as one from 2012 which found that 800 IU/day of vitamin D led to a non-significant trend in a reduction of TBIC in children.

Using a higher dose in a larger population from different areas of the world will help clarify results from these studies.

Source

Arnedo-Pena, A. et al. Vitamin D status and incidence of tuberculosis infection conversion in contacts of pulmonary tuberculosis patients: a prospective cohort study. Epidemiology and Infection, 2014.

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