Genetic differences influence calcium absorption

Genetic variations in a gene that helps regulate the body's response to vitamin D has given researchers new insight into why some children have higher bone densities.

"We found that variations in the receptor gene for vitamin D could predict differences in calcium absorption and bone density in healthy children," said Dr. Steven Abrams, a professor of pediatrics at Baylor College of Medicine who studies mineral metabolism in children at the CNRC. A major function of vitamin D is to promote the absorption of calcium from the intestines.

Abrams studied the relationship between three genetic variations of the vitamin D receptor gene at a site called Fok1 and markers of calcium status in 72 healthy, 7- to 12-year-old European-, African- and Mexican-American children. Abrams was interested in Fok1 because one variation, called the ff genotype, has been associated with lower bone mass in adults and children. The other two variations are known as FF and Ff genotypes.

The study found that children who had the FF genotype absorbed over 40 percent more calcium from their diets than those with the ff genotype, and 17 percent more than those whose genotype was Ff. The children with the FF genotype also had significantly greater bone density measurements.

A child's bone density is important because peak bone mass, which occurs in early adulthood, is considered a significant determinant of osteoporosis risk later in life.

Abrams cautioned that many factors, including diet and exercise, affect bone density.  "Further studies are needed to determine how the gene-related differences in calcium absorption and bone density found in this study affect osteoporosis risk," he said.

"This study provides evidence that genetic factors can lead to identifiable changes in the way the body uses calcium, which is a step towards understanding why some groups appear more likely to develop osteoporosis," he said.