Nutrition Action November 2010 : Page 6
of the salt, the kidney is going to get rid of calcium. It doesn’t have the skill to be selective. Q: Does too much vitamin A retinol increase the risk of hip fracture? A: That hasn’t gotten much farther than the observation that higher vitamin A levels have been associated with frac-tures in a couple of studies.We’ve known that vitamin A is very toxic to bone at extremely high levels. In fact, vitamin A toxicity is characterized by massive bone loss and coma. But whether typical levels are a risk, we don’t know. Nevertheless, I think it’s wise to avoid excess vitamin A. I would stick to no more than 2,000 to 3,000 IU of retinol per day. [See “The Bot-tom Line.”] When there weren’t many vitamin-D-fortifi ed foods or supplements, some doctors were recommending a double daily dose of multivitamins in order to get the 800 IU of vita-min D that some of us recom-mend for people over 70. That’s not a good idea because you could get too much vitamin A. Beta-carotene in fruits and vegetables isn’t associated with bone loss even though the body turns it into vitamin A. EXERCISE Q: Does exercise help? A: Absolutely. Aim for at least half an hour a day of weight-bearing exercise like walking or dancing. [See “Step On It!”] There’s no solid, unequivo-cal evidence for exactly what regimen and for how long and for how many days per week. All those details haven’t been worked out so you just have to do something reasonable. Q: Either strength training or aerobic? A: Yes. But with either kind, the spine seems to respond better, as do the hips, when you are in the upright position as opposed to lying down. That sends a dif-ferent signal to the bone. Q: How does weight-bearing exercise strengthen bones? A: This has been a big ques-tion for a long time. It appears 6 NUTRITION ACTION HEALTHLETTER ■ NOVEMBER 2010 2.Osteoclasts use enzymes to dissolve bone tissue. that the mechanical load from the weight is turned into a chemical signal by the osteocytes. These are the former osteo-blasts, the bone-forming cells, that get entrapped in the bone. For years we had thought that, once they did their job, they were just en-tombed, do-nothing cells, and that’s not right. They have tentacles that go out and touch one another and communicate the signal to build new bone tissue. MEDICATION Q: Are we treating the right people with drugs to prevent bone loss? A: Not exactly. I led a group that looked SUPER REMODEL Most of the adult skeleton is replaced about every 10 years. Remodeling repairs small cracks, gets rid of old bone, and frees up calcium in case the body needs it. 1. Bone-dissolving cells called osteoclasts approach old bone. at the potential impact of the National Osteoporosis Foundation’s latest guide on treatment. It’s based on the FRAX, or Fracture Risk Assessment Tool, which was developed by theWorld Health Organi-zation to estimate the 10-year risk of a fracture based on age, weight, family his-tory of fractures, etc. [See “What’s Your FRAX?” p. 4.] We found that people age 70 and older are practically all good candidates for treatment, but that those in their 50s are generally not good candidates. This is very important. If the new guide is right, then we’ve been overtreating women in their 50s and 60s and under-treating older women. Q: Do some women in their 50s and 60s need medica-tion? A: Yes. If you’ve had a prior spine or hip fracture, you are a candidate for treatment. And if a bone-density test shows a T-score of -2.5 or lower at the spine or hip—that means you already have osteoporosis—you don’t need a FRAX score. You need treatment, no matter what your age. Q: So the question is what to do about people whose bone density is low, but not low enough to be osteoporosis? 3. Bone-building cells called osteoblasts prepare to lay down a bone matrix made mostly of a protein called osteocalcin. 4. Calcium and phosphorus attach to the matrix and create new bone. A: Yes. Among women who have a T-score in what is called the osteopenia range—that is, between -1.0 and -2.5—over 40 percent of those in their 50s would have been candidates for treatment by the old guide. By the new guide, only about 8 percent are candidates. You see that huge shift. And among women in their 60s with osteopenia, around 55 percent by the old guide but only about 18 percent by the new guide are candidates for treatment. Q: What about older women? A: That hasn’t changed much. Among women in their 70s with osteopenia, about 60 percent should be candidates for treatment and by their 80s, about 90 percent would be candidates. Yet many older people are not particularly worried, and many Illustration: Loel Barr.