“Misconception: All you have to do is walk or do modest strength training exercises to build strong bones. Actually: Exercise has little or no effect on bone strength.”
This begins the article and really encapsulates the problem; it’s not precise enough. It claims walking isn’t enough to build strong bones (research does generally support this). It also claims that modest strength training doesn’t build strong bones (this is not necessarily true – modest needs to be defined and the individual’s training history must be accounted for). It then claims that exercise has little or no effect on bone strength (exercise is too vague; what type of exercise are we talking about?).
“…scientists did rigorous studies, asking if weight bearing exercise increased bone density in adults. They used DEXA machines, which measure bone density by hitting bones with X-rays. Those studies failed to find anything more than a minuscule exercise effect — on the order of 1 percent or less, which is too small to be clinically significant.”
First of all DEXA (bone density) has limitations. It’s a 2-dimensional surrogate for a 3-dimensional structure, the size, shape and composition of which all can influence bone strength. As the author notes, there are studies that show no change in bone density with exercise, but the author fails to mention that many studies do show that strong bones are associated with increased bone density (and vice versa). For example, Almstead et. al, 2011 show 2-7% increases in BMD after strength training. But the bigger oversight here is that very small (even 1%) increases in bone mass can in fact have a huge impact on strength. It depends on where the bone is added. If it’s added on the outer surface of your leg bone (femur) for example, the strength will go up because you’ve increased its polar moment of inertia.
“More recently, using new and very expensive machines that scan bone and are able to show its structure at a microscopic scale, they reported a tiny exercise effect in one part of the bone’s architecture known as the trabecula, little branches inside bone that link to each other. The cortical shell — the outer layer of bone — also seems to be slightly thicker with weight bearing exercise. But these are minute changes, noted Dr. Clifford Rosen, a bone researcher at the Maine Medical Research Institute. There is no evidence that they make bone stronger or protect it from osteoporosis, he said.”
First, these machines aren’t that new. Second, this line stunned me as I know Dr. Rosen. We have authored papers together. I emailed Dr. Rosen to ask if he actually said this and his response was, “A little out of context!!! The whole article was a bit out of it. Of course I never saw it before pub[lication].” This was as I expected, but it highlights another big problem. Even when the proper experts are interviewed, the message often gets garbled and they aren’t given a chance to proofread the message before it goes to the public.
“At this point nothing except injections of parathyroid hormone and, perhaps, a new injectable drug called abaloparatide now being tested in clinical trials, make bone denser and stronger.”
This is a completely unsupported claim. Again, we know that size, shape, and composition (quality) of bone all play a role in determining a bone’s strength. We know this from a combination of human and animals studies (check out my work in 2008 and the work of my mentor Karl Jepsen in 2013 as examples). The two literature groups, of which these two articles are a part, have to be examined together. And the message is clear, anything that imparts even small changes to the size, shape, or composition of bone can have an effect on its strength. The relationships are complicated, and still not fully understood, but they are real. Exercise in the form of weight training, is one very accessible means for humans to impart positive changes to their bone size and strength.
I emailed Gina Kolata after reading her article requesting that she take it down because, as written, it was too misleading to the public. In fact, beyond misleading I said it was dangerous as it undermines decades of research which support the effectiveness of weight training in keeping bones strong and preventing fractures. To date Gina has not responded to my email and the article remains live on the NY Times website