Children with vitamin A deficiency are at an increased risk of developing gastrointestinal and respiratory illnesses, according to a new study.

Researchers at the University of Michigan School of Public Health and Michigan State University found a link between low vitamin A levels and the incidence of diarrhea with vomiting and cough with fever, according to a news release.

Previous studies on Vitamin A deficiency had focused on infants and children younger than five years old, and have been somewhat inconsistent about the impact of vitamin A supplementation on respiratory and gastrointestinal illnesses.

"Studies of older children have included a range of micronutrients administered together, but no study had estimated the potential role of vitamin A alone in this age group," Eduardo Villamor, associate professor of epidemiology and senior author of the study, said in a statement.

For the study, researchers followed nearly 2,800 children, ages 5-12, in Bogota, Colombia, for a year. They measured markers of other micronutrients that are important to the immune system including zinc, iron, folate and vitamin B12, but only vitamin A was related to illness.

In their study, researchers found that 14 percent of the students were vitamin A-deficient, defined as blood levels less than 20 micrograms per deciliter.

"The association we found with vitamin A followed a dose-response pattern, in that higher blood concentrations of retinol were related to fewer symptoms," Villamor said.

Researchers found that for every 10 micrograms per deciliter of vitamin A or retinol present in the blood, children experienced 18 percent fewer days with diarrhea and vomiting, 10 percent fewer days of cough and fever, and 6 percent fewer visits to the doctor.

The team said more research is needed to determine if vitamin A supplementation can reduce the risk or severity of infection in the older children.

"As we have learned from vitamin A supplementation to younger children, which has shown mixed success in preventing illness, the picture is more complicated than it might appear," Villamor said.

He added that the effects of micronutrients, including vitamin A, could vary in different settings due to the underlying nutritional status of the population, "the epidemiologic patterns of the microorganisms that cause illness-whether viral, bacterial or parasitic-the age and possibly sex of children, and other factors. It's definitely uncertain whether supplementation is a one-fits-all solution."