A study published this month in the journal Pediatrics found that infants given multivitamin supplements before 6 months of age had increased risks of asthma and food allergies. The asthma link was stronger for African Americans than for other racial groups.
"What we found was that in giving multivitamins prior to 6 months of age, [there was a] 30 percent increased risk for asthma" in African American infants regardless of whether they were breast-fed, said lead investigator Joshua D. Milner, a clinical fellow in allergy and immunology at the National Institute of Allergy and Infectious Diseases. The increased risk for asthma among non-black babies who took multivitamins was not statistically significant.
Babies of all racial groups who were exclusively formula fed and given multivitamin/mineral drops had a 70 percent increased risk for food allergies, Milner said in a phone interview.
But researchers said the findings do not mean that parents should rush to take their children off multivitamins.
"This is the first time anybody has looked at this," said Rachel Y. Moon, a pediatrician at Children's National Medical Center who worked on the study. "This is just an association. . . . There needs to be further study done to figure out what that association is."
Researchers analyzed data from the 1988 National Center for Health Statistics (NCHS) National Maternal-Infant Health Survey, which followed about 8,000 mothers and their infants. The survey asked parents if they gave their children vitamin/mineral drops and whether their babies were breast- or bottle-fed. A 1991 follow-up survey asked the same parents if their children had developed specific health problems, including asthma and food allergies. Overall, about 10 percent of the children studied developed asthma, and about 5 percent developed food allergies.
Milner said he decided to do the study in 2001 after reading basic research and epidemiological reports on the effects of vitamin use.
The previous studies suggested that "certain individual vitamins had the capacity to alter the immune system in some ways," Milner said. Additional studies ideally would follow patients for many years.
"It would take a very large number of children . . . and years of follow-up before you're sure you've seen all the food allergies and asthma that are going to be diagnosed," Milner said, adding that in children, food allergies are typically diagnosed by age 4, and asthma by age 6.
His study also looked at cases of hay fever among survey respondents, but researchers did not find a significant change in risk related to multivitamin use.
The government survey's population was designed to include more minorities and other traditionally medically underserved groups, Milner said, so that NCHS could determine how health care was being delivered and used by those groups. African Americans made up 51 percent of participants, and 46 percent were white. About 50 percent of the group reported annual household incomes of less than $20,000, and 24 percent of the babies involved in the study had been born prematurely.
The surveys asked mothers how often and at what age they gave their children multivitamin supplements. Thirty-two percent reported giving their babies vitamins at least three times a week for at least a month before 3 months of age, 41 percent before 6 months of age and 42 percent supplemented at 3 years of age.
Some parents give their children multivitamin supplements because they are the only liquid sources of vitamin D.
"That's the only way it [vitamin D] comes in our country," said Frank Greer, a professor of pediatrics at the University of Wisconsin and a member of the American Academy of Pediatrics' (AAP) committee on nutrition. "It comes in a solution usually with vitamins A and B."
Vitamin D is synthesized by the body when the skin is exposed to sunlight. But the fear of skin cancer often causes parents to keep their children out of direct sunlight, and to cover them in sunscreen -- which decreases vitamin D production -- when they are outside.
People with darker skin pigmentation don't absorb vitamin D from the sun as well as those with lighter skin tones. This makes rates of rickets -- a rare childhood disease involving bone softening and weakening that is caused by vitamin D deficiency -- higher among black children, Milner said.
AAP has not issued guidelines for using multivitamin supplements. But in an effort to cut rickets risk, the group recommended in 2003 that all infants take in a minimum of 200 international units of vitamin D per day beginning at 2 months of age.
Doctors often recommend multivitamin supplementation for children who are breast-fed (vitamin D is very low in breast milk) or have chronic illnesses.
Still, parents of healthy, formula-fed babies (infant formula is enriched with vitamins) often use multivitamin supplements without a doctor's recommendation. Milner recommends that parents talk with their children's pediatrician if they have questions about using multivitamins.
"For the most part, doctors don't tell people to give their children multivitamins," he said. "My guess is that the majority of multivitamins that are given is because parents feel like it will make their child healthier. But it isn't really known what risks there are."