Micronutrients help fight disease — it's time to turn knowledge into action, say nutrition researchers Andrew Thorne-Lyman and Wafaie Fawzi.
Undernutrition in women and children is an underlying cause in 3.5 million deaths each year. And in developing countries, malnutrition accounts for over a third of the disease burden in children under five.
Malnutrition impairs immunity, while infection often depletes nutrient and energy stores, in turn leading to more frequent and severe infections. So malnutrition and infection act together in a vicious cycle that worsens health and can sometimes lead to death.
This cycle is particularly common in developing countries, creating a fertile landscape for infectious diseases such as measles, tuberculosis (TB), diarrhoeal disease and HIV/AIDS — often with devastating effects.
Part of the problem is that deficiencies of vitamins and minerals (micronutrients) are less visible than protein malnutrition. But they are pervasive in developing countriesand are major causes of death and disability.
Evidence linking micronutrient malnutrition and infectious disease dates back to the 1930s, when the 'anti-infective' properties of vitamin A received much attention from researchers and the public. The interest stemmed from studies showing vitamin A deficient animals and humans were abnormally susceptible to respiratory infections.
Other early research showed enough promise for cod-liver oil (a rich source of both vitamins D and A) and sunlight (which enables the body to produce vitamin D) to become common treatments for tuberculosis.
But interest in using these micronutrients to boost immunity waned with the introduction of antibiotics. It wasn't until the late 1970s that scientists began researching micronutrients and infection in humans in earnest — due in part to findings that Indonesian children with vitamin A deficiency were at significantly heightened risk of diarrhoea, respiratory infections and death.
We now know that vitamin A and zinc deficiencies contribute to the deaths of one million children each year. Other micronutrient deficiencies, such as iron, B vitamins, folate, selenium and vitamins C, D and E, are known to disrupt important functions in the immune system and often occur in people with chronic infections such as TB and HIV/AIDS.
And a growing body of research is revealing just how powerful tackling micronutrient malnutrition can be in preventing and treating infectious disease.
For example, clinical trials reveal that vitamin A supplements reduce mortality among preschool children by, on average, 23 per cent — however, there is some doubt about the safety and benefit of vitamin A supplements for infants under six months old and for HIV-infected people.
Zinc is another micronutrient with tremendous promise for saving lives. Studies show child deaths due to diarrhoea halve when zinc supplements are included as part of treatment.
Trials of different micronutrient supplements alongside drug treatment for TB have also yielded promising results, reducing mortality and improving treatment outcomes. Their effectiveness against drug-sensitive and multidrug-resistant TB needs further research.
And micronutrient supplements could help people living with HIV/AIDS. Despite the rapid roll out of antiretroviral therapy in developing countries, HIV remains the leading cause of infectious disease deaths worldwide. Co-infection with TB is common and deficiencies of multiple micronutrients in people infected with either or both diseases are well documented.
Daily multivitamin supplements have reduced HIV progression in several observational studies and randomised trials, as well significantly decreasing the risk of low birthweight, miscarriage and other adverse outcomes among HIV positive pregnant women.
Micronutrient supplements offer a low-cost way to improve the health of people with HIV — though of course they are no replacement for life-saving antiretroviral therapy.
Put it into practice
Decision-makers, as well as nutrition researchers, recognise that micronutrient interventions are cost-effective tools for improving health. In 2008, the Copenhagen Consensus Center, a development 'think-tank' based in Denmark, brought together leading economists and Nobel Laureates to create a list of development priorities. They ranked micronutrient interventions as the top priority out of more than 40 potential interventions.
Some donors and health communities have embraced micronutrient interventions. For example, treating measles with vitamin A is now standard care and semi-annual campaigns to distribute vitamin A capsules are a routine child-survival initiative in many countries.
Yet funding for micronutrient and other nutrition programmes remains disproportionately low. And progress in translating the science into real action has been variable.
For example, UNICEF and the WHO have both issued statements supporting zinc supplements, together with oral rehydration therapy, as standard in managing diarrhoeal disease.
But rolling out policies and programmes has been slow, burdened by funding issues and difficulties in establishing national policies.
And some micronutrient interventions — such as those for HIV or TB — are still either awaiting further confirmatory trials or have not yet been advocated as widespread interventions.
Micronutrient interventions offer a low-cost strategy for achieving large reductions in death and disability due to infectious disease yet remain underfunded.
Donors and developing country governments need to step up interventions to improve nutrition, so reducing the burden of infectious disease. It is high time to translate the findings of scientific studies on micronutrients and infectious disease into effective large-scale programmes.
Andrew Thorne-Lyman is a doctoral student, and Wafaie Fawzi a professor of nutrition and epidemiology, at the Harvard School of Public Health in the United States.
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See Letter to the Editor.