Vitamin D deficiency is not responsible for TB in children - study
Vitamin D deficiency has long been considered a risk factor for tuberculosis in adults as it impairs the immune response to the TB bug, but a new study by the University of Cape Town has found that low levels of the sunshine vitamin in children doesn’t necessarily make them susceptible to the illness.
In the study, published in the Clinical Infectious Diseases journal, which tracked infants from birth to seven years, researchers found that though vitamin D levels were extraordinarily low in the majority (81%) of these children, there was no relationship between TB incidence and vitamin D deficiency.
“We found a very high prevalence of vitamin D deficiency in infants. Surprisingly though, we found no relationship between vitamin D levels in early infancy and TB incidence during childhood regardless of the vitamin D cut-off used,” said co-author Prof Heather Zar, chair of the department of paediatrics and child health, who is also the director of the South African Medical Research Council Unit (MRC) on child and adolescent health at UCT.
“This was true when we used the entire follow-up time period (seven years) or when we only looked at children up to one year of age. Though we did not show a relationship, this is an important finding as it suggests that vitamin D supplementation may not be useful to prevent TB in this setting and with this population. Therefore, other interventions or relationships should be investigated further instead and we may need to reconsider regarding vitamin D and TB risk.”
Researchers followed about 774 infants in the Drakenstein Child Health Study cohort who had a vitamin D measurement between six and 10 weeks of age. Vitamin D levels were extraordinarily low with 81% of infants in the cohort defined as vitamin D deficient. They found a very high incidence of TB disease, among the seven-year-olds, the highest ever reported globally. This was the first study to examine the correlation of the deficiency in children.
Previous studies on adults had found a link between vitamin D and TB. People who develop TB often present with low vitamin D levels when they are diagnosed. A decade ago UCT and the National Institute for Medical Research (NIMR) in the UK found that vitamin D deficiency was extremely common in black Africans living in Cape Town, and was also associated with susceptibility to TB infection.
While HIV infection is a major cause of such immunocompromise, and the high prevalence of HIV infection in SA drives its TB epidemic, researchers said low levels of vitamin D also made people susceptible to the TB germ.
People living in Cape Town are at greater risk of vitamin D deficiency because the long winters compromise the sunlight’s ability to synthesise vitamin D.
Though no relationship has been found between low levels of the sunlight vitamin in children and TB, researchers found that children with the lowest vitamin D levels in early infancy were more likely to convert their tuberculin skin test in the first two years of life. “We also found high incidence of TB in this cohort,” added Zar.
“In settings with hyperendemic TB disease and where vitamin D deficiency is ubiquitous, such as SA, vitamin D concentrations in infancy may not predict subsequent tuberculosis disease in childhood.”
Leonardo Martinez, lead author and assistant professor at Boston University, said: “TB is a major cause of death and of illness in children, both within SA and more globally. Therefore, understanding factors that put young children at high risk of TB is important to create interventions for this group.”
“We would like to conduct further research on other vitamins and their relationship to TB. Though vitamin D did not predict incident TB in our cohort, we hypothesise that other vitamins, such as vitamin A, B, or C (or others), may be linked to TB. Therefore, we plan to look at these specific micronutrients in more depth. Also, we’d like to look at vitamin D levels through childhood, to see whether levels measured later may be associated with TB or other diseases,” he said.