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Dear List,
And here's the research summary on exercise for bones:
One list member challenged me to provide a reference to a Jane Brody
column (New York Times) I cited in which she said weight-bearing
exercise does not, per se, build bone. I couldn’t find it, so I wrote
Brody and amazingly, she answered! She doesn’t remember saying any
such thing. Challenges are good; they lead to better and stronger
information.
Here’s what Brody wrote:
“….the tug of large muscle groups on bone is what stimulates bone
strength, and the way you get that is thru regular weight-bearing
exercise. Preventing falls by improving balance reduces the risk of
fractures, especially in people whose bone density may be deficient.”
I also asked an ob/gyn friend about how exercise makes bones stronger.
He said the slight injury produced by aerobic exercise causes the body
to marshal its repair functions, so that just as a broken leg becomes
stronger in the spot where the break occurred, so are bones slightly
injured by exercise.
In addition, I did some on-line research into the question, but didn’t
find many scholarly articles I could read w/out paying a fee. The
upshot of my search, however, is a feeling that there is some
scientific controversy about exactly how exercise makes bones
stronger, not to mention controversy about the real meaning of bone
densitometry results (bone density is what we can measure, not
necessarily what matters). Below, the urls.
1. A nice primer on how bone regeneration works
http://courses.washington.edu/conj/bess/bone/bone2.html
2. There is a history of studies showing that exercise does prevent
help bone loss and/or reverse it. For instance, a meta-analysis of
studies from 1966 through 1996 on exercise and bone loss:
“The weighted OTs (overall treatment effects) for the RCTs
(randomized controlled trials) showed very consistently that the
exercise training programs prevented or reversed almost 1% of bone
loss per year in both LS (lumbar spine) and FN (femoral neck) for both
pre- and postmenopausal women.”
http://www.springerlink.com/content/ywv4w3m54tfx5kt0/
3. However, other, post-1996, studies argue the claim. I’ve spent
quite a number of hours on this, and cannot find many articles that I
can access for free, so I don’t know what’s in some of the scholarly
work that shows up in a Google search. But for whatever it’s worth:
abstract of 1999 article
“….the rate of bone loss for postmenopausal women can be slowed by
exercise, should be viewed with great caution: there was only a
partially significant finding that strength exercises provided this
benefit in the group calculations, and other statistically-significant
results were obtained by the exclusion of certain groups of
participants.”
http://www.library.nhs.uk/womenshealth/ViewResource.aspx?resID=240004
4. 2001 publication testing effect of exercise plus alendronate
(Fosamax) in women early in menopause (when bone loss is high)
“Exercise alone had no effect on bone mass at the lumbar spine or
femoral neck; it had neither an additive nor an interactive effect
with alendronate at these bone sites. However, at the distal tibia the
mean increase of 3.6% (0.3–7.1%) in the section modulus (that is, bone
strength) and 3.7% (0.1–7.3%) increase in the ratio of cortical bone
to total bone area were statistically significant in the exercise
group compared to the nonexercise group, indicating exercise-induced
thickening of the bone cortex. Bone turnover was reduced in
alendronate groups only.”
http://linkinghub.elsevier.com/retrieve/pii/S8756328203000826
5. bone density an insufficient measurement to predict fracture risk;
abstract of paper that makes a distinction between bone density and
overall bone quality
http://www.ncbi.nlm.nih.gov/pubmed/15763602?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DiscoveryPanel.Pubmed_Discovery_RA&linkpos=2&log$=relatedreviews&logdbfrom=pubmed
6. “….indicate that bone loss is not a constant process over time but
rather exhibits cyclical damping oscillations.”
http://linkinghub.elsevier.com/retrieve/pii/S8756328202009018
7. and on a completely different note:
“The bone remodeling response to exercise training in women not
taking HRT was not significantly different from those not exercising.
However, the direction of change suggests an elevation in bone
remodeling in response to exercise training, a phenomenon usually
associated with bone loss.”
http://www.ncbi.nlm.nih.gov/pubmed/12574871?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DiscoveryPanel.Pubmed_Discovery_RA&linkpos=5&log$=relatedarticles&logdbfrom=pubmed
I have tried (above) to stick to scientifically reliable references.
In searching for relevant information, I’ve read myriad articles
claiming this or that. But when I check the medical researchers
mentioned in those non-medical articles, it generally turns out the
non-medical writer has shamelessly cherry-picked. For example, one
sensible-sounding website article cites a meta-analysis of research on
the efficacy of calcium for bones, and says the research shows that
it’s Vitamin D that counts, not calcium. Hmmm. What the researchers
actually say, in their abstract,
"Subgroup analyses suggested that the effect size was independent of
calcium supplementation, type of vitamin D, duration of therapy, and
sex, but reduced sample sizes made the results statistically
nonsignificant for calcium supplementation, cholecalciferol, and among
men."
http://jama.ama-assn.org/cgi/content/abstract/291/16/1999
In addition, the study is now 10 years old.
Bottom line: there is significant scientific controversy about what
works and what does not.
cheers,
Mary B.
NYC
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