The study made at Malmö University examined the dental health of more than 900 five-year olds in central Skåne through records from child health and public dental clinics.
One reason cited by the researchers as to why underweight children are at a high risk for tooth decay can be due to parental concerns about their child's weight development. As a consequence, they allow their children to eat what they want at irregular hours, resulting in the diet that contains more sugar.
Previous studies have shown that overweight children have an increased risk of tooth decay, but in the current study, the scientists did not see the link.
According to Lars Matsson, professor of paedodontics at the Faculty of Odontology at the university, the research results were surprising. The study was initially undertaken to examine overweight children, but it was the underweight children who turned out to have the most tooth decay.
"We have found a risk group that we did not recognise before," said Matsson. "In dental care, we must be more attentive to these children, examine them carefully and inform parents so they can give them a good and healthy diet. Child care centres must also pay attention and help these children."
The study used height and weight data from child health care authorities to calculate the children's BMI, or body mass index, which determines health status and the chances of a long life. These were then compared with the the tooth decay data from public dental clinics.
"The underweight children had significantly more tooth decay than children of normal weight," said Matsson. "Among these little kids, we know that there are some who are picky and may not eat as much and parents become anxious. As such, they can eat whenever they want instead and choose what they want. Often, it is sweet."
A modified diet pattern is key to improving dental health, he said.
"It's the same old," said Matsson. "We want the parents to give their children three main objectives for the day and snacks that consist of sandwiches and fruit rather than candy and ice cream. Sweet juice should also be avoided. Milk and sandwiches are better than sweets."