The research was based on 78 girls and 84 boys, who were studied from the time they began puberty until they reached sexual maturity. The investigators found that adult bone mineral density was influenced by age at puberty onset, with greater bone mass linked to early puberty and less bone mass associated with later puberty. However, bone strength did not seem to be affected by how long puberty lasted.

"Puberty has a significant role in bone development," study leader Dr. Vicente Gilsanz, director of clinical imaging at the Saban Research Institute of Children's Hospital Los Angeles, said in a hospital news release.

"During this time, bones lengthen and increase in density. At the end of puberty the epiphyseal plates close, terminating the ability of the bones to lengthen. When this occurs, the teenager has reached their maximum adult height and peak bone mass," Gilsanz explained.

Reduced bone mineral density leads to osteoporosis, which affects 55 percent of Americans aged 50 and older.

The normal rate of bone mass decline in adulthood is about 1 to 2 percent each year. This means that a 10 to 20 percent increase in bone density resulting from a naturally early puberty could provide an additional 10 to 20 years of protection against normal age-related decline in bone strength, according to the researchers.

The study was published in the January issue of the Journal of Pediatrics.

Pediatricians have long understood the role of pediatric bone development in osteoporosis prevention. The tween and teen years are critical for bone development because most bone mass accumulates during this time.

In the years of peak skeletal growth, teenagers accumulate more than 25 percent of adult bone.

By the time teens finish their growth spurts around age 17, 90 percent of their adult bone mass is established.

Following the teen years, bones continue to increase in density until a person is about age 30.

The need for calcium in the diet.

Calcium is critical to building bone mass to support physical activity throughout life and to reduce the risk of bone fractures, especially those due to osteoporosis.

The onset of osteoporosis later in life is influenced by two important factors:

•   Peak bone mass attained in the first two to three decades of life

•   The rate at which bone is lost in the later years

Although the effects of low calcium consumption may not be visible in childhood, lack of adequate calcium intake puts young people at increased risk for osteoporosis later in life.

Other foods, including dark green, leafy vegetables such as kale, are also healthy dietary sources of calcium. But, it takes 11 to 14 servings of kale to get the same amount of calcium in 3 or 4 8-ounce glasses of milk.

In addition to calcium, milk provides other essential nutrients that are important for optimal bone health and development, including:

•       Vitamins D, A, and B12

•       Potassium

•       Magnesium

•       Phosphorous

•       Riboflavin

•       Protein

The role of physical activity in bone development.

Weight-bearing physical activity helps to determine the strength, shape, and mass of bone.

Activities such as running, dancing, and climbing stairs, as well as those that increase strength, such as weight lifting, can help bone development. For children and teenagers, some of the best weight-bearing activities include team sports, such as basketball, volleyball, soccer, and softball.

Studies show that absence of physical activity results in a loss of bone mass, especially during long periods of immobilization or inactivity.