Osteopenia and Osteoporosis in Cystic Fibrosis Patients

Condensed from the talk by Laura Bachrach, M.D.

Fall 1994

Dr. Laura Bachrach, Acting Associate Professor of Pediatrics at the Stanford University Medical Center, gave a general overview of her study, funded by CFRI, of osteopenia (decreased bone mass) and osteoporosis (bone loss to the point of brittleness and tendency to fracture) specifically in relation to patients with cystic fibrosis. The tendency toward lower bone mass in children and adults with cystic fibrosis was remarkable. Dr. Bachrach informed the group that bone mass density is mainly influenced by heredity (40-70% of peak bone mass is determined this way). However there were several other key factors that were especially important to people in the CF population. These include the amount of weight-bearing activity a person does, actual body mass of the person (those who are underweight are at increased risk for lower bone density), adequate intake of calcium, and proper levels of sex steroids. There are specific ages when bone mass acquisition is especially critical. In infancy, gains are rapid; in childhood they slow down. But in adolescence, at the onset of puberty, the rate picks up again. 50% of adult bone mass is acquired during adolescence! The rate slows again as adults enter the third decade, and there are no net gains after this decade. People with CF are at increased risk of lower bone density because of their lower body weight and inadequate calcium levels. It's important to point out that it's not enough to just increase calcium intake. Calcium's absorption is directly affected by vitamin D levels in the body. Because vitamin D is a fat-soluble vitamin, people with CF often have trouble absorbing this vitamin. In her tests, Bachrach realized that 40% of the subjects had low vitamin D levels. Another contributing factor to bone-density loss is glucocorticoid therapies. Also, prednisone and other steroids cause calcium loss. Finally, delayed puberty and gonadal dysfunction means that there are low levels of sex steroids in both males and females with CF. These sex steroids play an important role in bone mineral acquisition. Dr. Bachrach said that she is addressing these deficits in several ways. Nutritional supplements (both calcium and vitamin D) are critical. Recommended daily levels of calcium intake are as follows: 360-540 mg./day for infants, 800 mg./day during childhood, 1500 mg./day between ages 10-24, and 800 mg./day for age 25 and up. This is considered a minimum for CF patients. Other ways of improving bone acquisition include optimizing glucocorticoid doses, and monitoring sex steroid levels and supplementing when necessary. She mentioned Calcitonin and bisphosphonates as drugs currently available in the treatment in osteoporosis, however warned of side effects. Dr. Bachrach made a few other interesting points. First of all, CF disease severity could not necessarily predict bone density problems. And other good news is that there were ways of addressing the problems as mentioned above, and it did not take much of a gain in bone density to afford a high payoff. Just a 5% gain in bone mass gives a lifetime reduction of risk of 40%!

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