An 18-year-old woman with Crohn’s disease (diagnosed 3 years ago) came to my office for advice regarding management of osteoporosis. Her bone density was low for her age, and she had three low-impact fractures of her long bones in the preceding 4 years.
Loss of weight after the onset of Crohn’s disease, subsequent loss of periods, inflammation associated with her underlying diagnosis, and early treatment with glucocorticoids (known to have deleterious effects on bone) were believed to have caused osteoporosis in this young woman.
A few months previously, she was switched to a medication that doesn’t impair bone health and glucocorticoids were discontinued; her weight began to improve, and her Crohn’s disease was now in remission. Her menses had resumed about 3 months before her visit to my clinic after a prolonged period without periods. She was on calcium and vitamin D supplements, with normal levels of vitamin D.
Many factors determine bone health including (but not limited to) genetics, nutritional status, exercise activity (with mechanical loading of bones), macro- and micronutrient intake, hormonal status, chronic inflammation and other disease states, and medication use.
Exercise certainly has beneficial effects on bone. Bone-loading activities increase bone formation through the activation of certain cells in bone called osteocytes, which serve as mechanosensors and sense bone loading. Osteocytes make a hormone called sclerostin, which typically inhibits bone formation. When osteocytes sense bone-loading activities, sclerostin secretion reduces, allowing for increased bone formation.
Consistent with this, investigators in Canada have demonstrated greater increases in bone density and strength in schoolchildren who engage in moderate to vigorous physical activity, particularly bone-loading exercise, during the school day, compared with those who don’t (J Bone Miner Res. 2007 Mar;22:434-46; J Bone Miner Res. 2017 Jul;32:1525-36). In females, normal levels of estrogen seem necessary for osteocytes to bring about these effects after bone-loading activities. This is probably one of several reasons why athletes who lose their periods (indicative of low estrogen levels) and develop low bone density with an increased risk for fracture even when they are still at a normal weight (J Clin Endocrinol Metab. 2018 Jun 1;103:2392-402; Med Sci Sports Exerc. 2015 Aug;47:1577-86).
One concern around prescribing bone-loading activity or exercise to persons with osteoporosis is whether it would increase the risk for fracture from the impact on fragile bone. The extent of bone loading safe for fragile bone can be difficult to determine. Furthermore, excessive exercise may worsen bone health by causing weight loss or loss of periods in women. Very careful monitoring may be necessary to ensure that energy balance is maintained. Therefore, the nature and volume of exercise should be discussed with one’s doctor or physical therapist as well as a dietitian (if the patient is seeing one).
In patients with osteoporosis, high-impact activities such as jumping; repetitive impact activities such as running or jogging; and bending and twisting activities such as touching one’s toes, golf, tennis, and bowling aren’t recommended because they increase the risk for fracture. Even yoga poses should be discussed, because some may increase the risk for compression fractures of the vertebrae in the spine.
Strength and resistance training are generally believed to be good for bones. Strength training involves activities that build muscle strength and mass. Resistance training builds muscle strength, mass, and endurance by making muscles work against some form of resistance. Such activities include weight training with free weights or weight machines, use of resistance bands, and use of one’s own body to strengthen major muscle groups (such as through push-ups, squats, lunges, and gluteus maximus extension).
Some amount of weight-bearing aerobic training is also recommended, including walking, low-impact aerobics, the elliptical, and stair-climbing. Non–weight-bearing activities, such as swimming and cycling, typically don’t contribute to improving bone density.
In older individuals with osteoporosis, agility exercises are particularly useful to reduce the fall risk (J Am Geriatr Soc. 2004 May;52:657-65; CMAJ. 2002 Oct 29;167:997-1004). These can be structured to improve hand-eye coordination, foot-eye coordination, static and dynamic balance, and reaction time. Agility exercises with resistance training help improve bone density in older women.
An optimal exercise regimen includes a combination of strength and resistance training; weight-bearing aerobic training; and exercises that build flexibility, stability, and balance. A doctor, physical therapist, or trainer with expertise in the right combination of exercises should be consulted to ensure optimal effects on bone and general health.
In those at risk for overexercising to the point that they start to lose weight or lose their periods, and certainly in all women with disordered eating patterns, a dietitian should be part of the decision team to ensure that energy balance is maintained. In this group, particularly in very-low-weight women with eating disorders, exercise activity is often limited until they reach a healthier weight, and ideally after their menses resume.
For my patient with Crohn’s disease, I recommended that she see a physical therapist and a dietitian for guidance about a graded increase in exercise activity and an exercise regimen that would work best for her. I assess her bone density annually using dual-energy x-ray absorptiometry. Her bone density has gradually improved with the combination of weight gain, resumption of menses, medications for Crohn’s disease that do not affect bone deleteriously, remission of Crohn’s disease, and her exercise regimen.
Dr. Misra is chief of the division of pediatric endocrinology at Mass General Hospital for Children and professor in the department of pediatrics at Harvard Medical School, both in Boston. She reported conflicts of interest with AbbVie, Sanofi, and Ipsen.
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