If species, particularly bees, that pollinate our crops continue to decline it could put people in some developing countries at risk of malnutrition, a study indicates.

Researchers at the University of Vermont and at Harvard University have conducted a study connecting the foods people actually eat in four developing countries to the pollination requirements of those crops providing that food and its nutrients.

"The take-home is: pollinator declines can really matter to human health, with quite scary numbers for vitamin A deficiencies, for example," says Vermont researcher Taylor Ricketts, co-leader of the study, "which can lead to blindness and increase death rates for some diseases, including malaria."

Bees are not the only pollinators showing a decline, researchers say, as many species that along with bees pollinate as much as 40 percent of the globe's nutrients show worrying reductions in numbers.

The researchers found that in several human populations the loss of pollinating species could see as much as 56 percent of the people ending up malnourished.

They cite Mozambique as an example, where many children and their mothers have trouble meeting their need for vital nutrients, particularly vitamin A.

More than one in four people in the world are suffering from some degree of vitamin and mineral deficiencies, the researchers say, a figure that could increase as pollinating species decrease.

"Continued declines of pollinator populations could have drastic consequences for global public health," the research team wrote in the journal PLoS ONE.

Some previous studies have attempted to link number of pollinators to crop yields.

"But to evaluate whether pollinator declines will really affect human nutrition, you need to know what people are eating," says study co-leader Samuel Myers at the Harvard School of Public Health.

So for their study the researchers analyzed the full trail from pollinators to detailed survey data about the daily diets of people in parts of Mozambique, Zambia, Bangladesh and Uganda.

"How much mango? How much fish?" explains Ricketts. "And from that kind of data we can find out if they get enough vitamin A, calcium, folate, iron and zinc."

The study highlights the fact that rapid alterations of Earth's natural systems -- in this case the significant drop in available pollinating species -- can have substantial effects on human health, the researchers say.

"Ecosystem damage can damage human health," Ricketts says, "so conservation can be thought of as an investment in public health."