Deficiency in vitamin A (<200 µg/L) may predict the risk of incident tuberculosis (TB) in individuals with household exposure to a person with TB, a recent study has found.
Researchers used baseline blood samples from a Peruvian cohort of HIV-negative individuals (n=6,751) who had been exposed to patients with pulmonary TB (indexed patients) in their households. A total of 180 household contacts who developed pulmonary TB between 15 days to 1 year after index patient enrolment (cases) were compared with randomly matched household contacts who did not develop TB (controls, n=709).
Among the household contacts, baseline vitamin A deficiency, as assessed by blood testing, was associated with a significantly increased risk of TB, after adjusting for BMI, socioeconomic status, nutritional factors, and other comorbidities (adjusted odds ratio [adjOR], 10.53, 95 percent confidence interval [CI], 3.73–29.70; p<0.001). [Clin Infect Dis 2017;doi:10.1093/cid/cix476]
The findings were consistent with previous in vitro studies which demonstrated a dose-dependent inhibition of Mycobacterium tuberculosis (Mtb) growth in culture due to vitamin A and its metabolites. [PLoS One 2012;doi:10.1371/journal.pone.0029631; Int J Infect Dis 2014;26:37-43]
“Mtb has been shown to use host lipids as a nutrient source, and host cholesterol mediates Mtb persistence and survival within macrophages. Taken together, these findings suggest that low vitamin A levels may impair host’s ability to control TB infection after exposure,” said the researchers.
In case the relationship between vitamin A deficiency and TB progression proves to be causal, routine supplementation of vitamin A among high TB risk individuals may provide a safe, effective, and relatively inexpensive means of preventing TB progression, said the researchers.
Although previous evidence has shown a decreased incidence of TB with improved socioeconomic and nutritional status, [Int J Tuberc Lung Dis 2004;8:286-298] there are no conclusive studies on the association between vitamin A and TB, noted the researchers.
On the other hand, it has been postulated that focusing on TB treatment could lead to the improvement or resolution of micronutrient deficiencies associated with active TB, including vitamin A levels. [Cochrane Database Syst Rev 2011;11:CD006086]
Aside from the relatively short follow-up period considering the slow TB pathogenesis, previous Bacillus Calmette-Guérin (BCG) vaccination might have influenced the results, noted the researchers. “[As] almost all our study participants had been vaccinated with BCG … we are unable to distinguish between the possibilities that vitamin A enhanced BCG-induced adaptive immunity or provided direct protection against TB progression,” they said.
“Our [findings] raise the possibility that screening for vitamin A levels among people at high risk for TB could help identify those likely to develop disease in the near future so they could be targeted for early intervention,” said the researchers.