The study followed nearly 2,800 children, ages 5-12 over the course of a year in the US.
Researchers at the University of Michigan School of Public Health and Michigan State University found that children with less vitamin A in their blood got sick more often with diarrhoea with vomiting and cough with fever.
"No study had estimated the potential role of vitamin A alone in this age group" of children between 5 and 12, said Dr Eduardo Villamor, senior author of the study.
Researchers said more research is needed to determine if vitamin A supplementation can reduce the risk or severity of infection in the older children.
The researchers also studied other micro-nutrients that are important to the immune system, including zinc, iron, folate and vitamin B12. But only vitamin A was related to illness.
The study found that for every 10 micrograms per decilitre of vitamin A present in the blood, children experienced 18 per cent fewer days with diarrhoea and vomiting, 10 per cent fewer days of cough and fever, and 6 per cent fewer visits to the doctor.
Villamor said the effects of vitamin A could vary in different countries due to differences in diet and the microorganisms that cause illness.
The age and possibly sex of children could also be factors, he said.
He said that it's uncertain whether giving children vitamin A pills will be an easy solution.
The study was published in the Journal of Nutrition.