Loss of pollinators could lead to a rise in disease
Amidst the buzz of concern about declining pollinator populations, it’s common to hear that bees and the like are responsible for somewhere around 30 to 40 percent of the food we eat. A study published last month in PLoS ONE provides the first rigorous test of such claims, finding that in some areas of the developing world, loss of pollinators is likely to increase nutrient deficiencies and make people more vulnerable to dying from common infectious diseases.
To reach these conclusions, researchers from the University of Vermont and the Harvard School of Public Health wove together several large sets of data collected in previous studies.
First, they assembled detailed information about what people actually eat on a daily basis from dietary surveys conducted in Zambia, Uganda, Mozambique, and Bangladesh. To this they added measures of the degree to which different food crops depend on animal pollination, and of the amount of vitamin A, calcium, folate, iron, and zinc found in different foods. This enabled them to calculate how the availability of these five essential nutrients would change if animal pollinators disappeared.
For example, people tend to get most of their calcium from dairy products, the production of which doesn’t depend on pollinators. By contrast, at least 69 percent of the vitamin A in children’s diets comes from fruit and vegetables, many of which are animal pollinated. Kids also get a lot of their zinc from vegetables, but not animal-pollinated varieties.
Vitamin A emerged as the most pollinator-dependent nutrient in the analysis. However, the percentage of children who would become deficient if pollinators disappeared varied from country to country. In Bangladesh, the loss of pollinators would have little effect on children’s vitamin A intake, largely because diets are already so poor. Pollinator loss would also have little effect in on vitamin A deficiency in Zambia, because diets there tend to be rather high in the nutrient. But the disappearance of pollinators would likely render 15 percent of children in Uganda and 56 percent of those in Mozambique deficient in vitamin A, the researchers found.
In turn, that could make them more vulnerable to common infectious diseases, the researchers say. Vitamin A is important for immune system function, and deficiency of this nutrient doubles children’s risk of dying from conditions like diarrhea, malaria, and measles.
In the United States, measles is primarily linked to declining vaccinations, not declining bee populations. But in the developing world, where most cases of measles occur, nutrition can have a big effect on a child’s chance of recovering from the disease.
Today, vitamin A deficiency is responsible for over one-fifth of deaths from measles, diarrhea, and malaria in children, and is linked to an estimated 800,000 deaths of women and children each year. That number that could increase substantially if pollinators continue to decline, the study suggests.
To be sure, the new study is a bit of a blunt instrument. The researchers only compared the current availability of nutrients to the availability if animal pollinators disappeared entirely, and they assumed that people wouldn’t change their diets if animal-pollinated foods became scarce. (Also, they refer to the current situation as “full pollination,” which seems like an example of a shifting baseline if ever there was one.) Still, the study provides one of the most careful, quantitative reminders yet of the links between pollinators’ health and our own. – Sarah DeWeerdt | 3 February 2015
Source: Ellis A.M., S.S. Myers, and T.H. Ricketts. 2015. Do pollinators contribute to nutritional health? PLoS ONE DOI: 10.1371/journal.pone.0114805
Header image: Insect pollinator on a mango blossom, which produces fruit high in vitamin A. Credit: S.Kiranjot Singh Malhotra | flickr (Creative Commons license)
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