Bone constantly undergoes a renewal process. Old bone is broken down and resorbed by the body and is replaced by new bone. From birth through the childhood years, bone formation occurs at a faster rate than bone loss to accommodate the growing skeleton. Even when a child has reached his/her final height, new bone growth outpaces bone loss. During this period, bones become stronger and denser. The process continues until a person reaches "peak" or maximum bone mass. The National Osteoporosis Foundation reports 85 to 90 percent of adult bone mass is attained by about age 18 in girls and 20 in boys.

Sometime after peak bone mass is achieved, the ratio of bone formation/bone loss slowly shifts. By middle age, bone loss occurs more rapidly than new bone is formed. Bone loss accelerates in women after menopause.

Children, Vitamin D and Bones

Calcium is an important nutrient for building strong bones. However, the body needs vitamin D to absorb calcium. One of the main sources of vitamin D is sunlight (the skin converts UV rays into vitamin D). Vitamin D can also be found in fortified milk, liver, fatty fish and egg yolks. If a person doesn't get enough vitamin D, the body can't use calcium to build bone, increasing the risk for developing low bone mass or osteoporosis.

Researchers studied a group of children referred to a specialized clinic for pediatric bone disorders. All the children were diagnosed with either low bone mass or osteoporosis. The investigators found 80 percent of the children had insufficient levels of vitamin D. About 20 percent of them had a vitamin D deficiency.

Catherine Gordon, M.D., is a Pediatric Endocrinologist at Children's Hospital Boston. She and her colleagues recently tested vitamin D levels in 380 healthy infants and toddlers. They found 40 percent of the children had suboptimal (below recommended standards) levels of vitamin D. More than 12 percent of the children had a vitamin D deficiency. None of the children had any signs of bone problems. Yet, among those in the deficiency group, one-third had X-ray evidence of bone demineralization (bone loss).

The risk for low levels of vitamin D was higher in breast-fed babies. Gordon hypothesizes that mom's aren't getting enough of the vitamin, and thus, don't have sufficient levels in their breast milk. She cautions children who don't get enough vitamin D won't reach their peak bone mass and may be more at risk for osteoporosis later in life.

Currently, doctors don't screen infants and children for vitamin D levels. So Gordon recommends vitamin D supplements for pregnant and breastfeeding moms and at least 200 IU/day for children. Supplementation with vitamin D (and maybe even calcium) may be especially important for children who have experienced bone fractures, those who don't drink milk and children who don't spend any time in the sun.

For general information on bone density or osteoporosis:

National Institutes of Health Osteoporosis and Related Diseases ~ National Resource Center

National Osteoporosis Foundation