The risk of childhood cancer after neonatal exposure to vitamin K.

BACKGROUND: Two recent studies have found that infants who received intramuscular vitamin K were at twice the expected risk for cancer during childhood. Since nearly all newborns in the United States receive this drug, the public health implications of this association, if confirmed, would be substantial.
METHODS: We examined the relation between vitamin K and cancer in a nested case-control study that used data from the Collaborative Perinatal Project, a multi-center, prospective study of pregnancy, delivery, and childhood. Among 54,795 children born from 1959 through 1966, 48 cases of cancer were diagnosed after the first day of life and before the eighth birthday. Each case child was matched with five randomly selected controls whose last study visit occurred at or after the age when the case child's cancer was diagnosed. Exposure to vitamin K was determined from study forms and medical records.
RESULTS: Vitamin K had been administered to 68 percent of the 44 case children and 71 percent of the 226 controls for whom data were available (matched odds ratio, 0.84; 95 percent confidence interval, 0.41 to 1.71). The odds ratio was 0.47 (95 percent confidence interval, 0.14 to 1.55) for leukemia and 1.08 (95 percent confidence interval, 0.45 to 2.61) for other cancers. Sequential adjustment for potential confounding factors did not change the results substantially.
CONCLUSIONS: We found no association between exposure to vitamin K and an increased risk of any childhood cancer or of all childhood cancers combined, although a slightly increased risk could not be ruled out. The benefits of neonatal vitamin K prophylaxis against hemorrhagic disease have been well described. Unless other evidence supporting an association between vitamin K and cancer appears, there is no reason to abandon the routine administration of vitamin K to newborns.