Australasian Science: Australia's authority on science since 1938

Vitamin D Deficiency Linked to Tuberculosis

By Stephen Luntz

Outbreaks of tuberculosis in Australia, particularly in the southern states, are a delayed response to low exposure to sunlight, the Victorian Infectious Diseases Reference Laboratory has proposed in the journal Emerging Infectious Diseases.

TB notifications were 24% higher in September–December than January–August Australia-wide, but this gap is 37% in Victoria and Tasmania.

Ms Jennifer MacLachlan and Dr Benjamin Cowie told a conference of the Australian Society for Infectious Diseases: “Although ecological studies such as this cannot establish causation, these findings support an association between vitamin D deficiency and the incidence of TB in Australia. This has implications for the tailoring of sun exposure messages to Australians most at risk of both vitamin D deficiency and TB, such as those born overseas and Aboriginal and Torres Strait Islander people.

“Blanket recommendations regarding reducing sun exposure for all Australians, particularly in winter months, may not be optimal. We need to balance the risk of skin cancer from too much sun exposure with maintaining adequate vitamin D levels.”

Other diseases peak in early spring, which is usually attributed to higher transmission from people staying inside or infectious agents surviving longer in cold conditions. However, MacLachlan says that “studies show there is a molecular mechanism for vitamin D to affect response to the TB bacteria,” making the connection particularly likely in this case. Moreover, she believes that the greater seasonal variation in states with the lowest winter sun adds credibility to the vitamin D connection.

“Other studies show there is a bit of a lag between exposure to UV light and vitamin D levels, and then a further lag to factors like bone protection,” MacLachlan says. Consequently she finds a late-year peak consistent with vitamin D deficiency. She adds that insufficient vitamin D may be a contributing factor to the spread of other infectious diseases, but the connection is less clear in the absence of molecular evidence.

Many TB notifications occur when a pre-existing disease flares up, which is sometimes triggered by a weakened immune system. “The data we had did not distinguish between new infections and reoccurrences,” MacLachlan says. She hopes to rectify this in future, which may shed even more light on the association.

Aside from seeking more personal guidance on the most appropriate levels of sun exposure, MacLachlan suggests that people consider taking vitamin D supplements, particularly those who may have been exposed to TB.