Low levels of vitamin A may fuel TB risk

Previous studies have suggested that vitamin A modulates the immune system and may ward off infection. However, just how vitamin A might affect the risk for TB has, up until now, remained unclear and a matter of debate.

People with low levels of vitamin A living with individuals sick with tuberculosis may be 10 times more likely to develop the disease than people with high levels of the nutrient, according to research led by investigators at Harvard Medical School, United States (U.S.).


The findings, published May 20 in Clinical Infectious Diseases, are based on an analysis of blood drawn from more than 6,000 household contacts of people diagnosed with TB in Lima, Peru.


The study findings do not prove a cause-and-effect relationship between vitamin A levels and TB disease, the researchers caution, but the potent link between the two suggests that vitamin A supplementation might be an important part of controlling the spread of TB — one of the leading causes of death worldwide.

“This is one of the strongest risk factors reported in a large epidemiological study in years,” said senior author Megan Murray, the Ronda Stryker and William Johnston Professor of Global Health at Harvard Medical School. “If the link is affirmed in a clinical trial of vitamin A supplementation, it would make a powerful case for using this approach to prevent TB in people at high risk of disease.”


A 10-fold increase in risk is striking, the investigators said. To put it in perspective, smoking tobacco increases the risk for heart disease two to four times, according to the Centers for Disease Control and Prevention.


More than 1.8 million people died from TB in 2015. TB strikes hardest in low- and middle-income countries, where vitamin A deficiency can affect up to 30 percent of the population.


“It’s exciting to think that something as simple and inexpensive as supplementing people’s diets with vitamin A may be a powerful tool for preventing TB,” Murray said.


Vitamin A, also known as retinol, is best known among public health experts for its association with blindness. Healthy levels of the nutrient have been defined as those needed to prevent damage to eyesight. Previous studies have suggested that vitamin A modulates the immune system and may ward off infection. However, just how vitamin A might affect the risk for TB has, up until now, remained unclear and a matter of debate.