Episode 53 | Dr. Susan Bloomfield, Ph.D. | Unexpected Ways to Boost Bone Density
Kathy Smith: Just starting out, you distinguished yourself in this field of bone research, but what attracted you to the field and, specifically, the physiology of bones?
Susan Bloomfield: My background is in a discipline called exercise physiology. Physiologists study the function rather than structure usually. We’re interested in how body systems work, how they adapt to different stressors. I had spent a lot of time early in my career working in a very active research lab at Washington University School of Medicine with some very bright, post-doctoral fellows and faculty. The focus there was largely on cardiovascular health and metabolic health, which are all important issues as they relate to exercise interventions. But when some years later I decided that I really did want to make research one focus of my career and went back to doctoral work, I decided I would really like to explore a new niche area.
At the time–this is early 80s–there were only a few people investigating the impact of exercise on bone health. Part of it was related to the fact that the technology we had then to measure bone density as a main circuit measure of bone strength and, therefore, bone health, was just in its infancy. So, part of it was technology-limited. But I got into it at that time and was very fortunate to have some great opportunities at the Ohio State University where I did my doctoral work, and that launched my career in this area of bone research.
Kathy Smith: Let’s just help the audience understand. Explain the bone and the structure of the bone and how does bone grow and how do we create bone?
Susan Bloomfield: Ok, I’ll try to keep this brief. It’s tough, but bone is a really–I, of course, am biased. I think it’s the most fascinating tissue in the body, because it is a smart tissue. It can repair itself and, for instance, if you fracture a bone, given good health, the bone tissue will form a large callus in helping heal and stabilize the initial fracture. But, then, eventually over time, it will remodel that callus and you’ll end up with a bone that looks identical to the original bone.
So, bone is an interesting tissue because most of it is what we call extracellular matrix. In other words, it’s material outside of the cell. So, the cellular component, what we think of bone tissue, is much smaller than, say, in your liver or muscle. Because almost virtually all the component of that soft tissue is comprised of cells and their contents.
The bone cells that form new bone tissue are called osteoblasts, but for ease of reference, I’ll just call them the bone-forming cells here. They actually create new bone by secreting proteins and related molecules that form what we call non-mineralized bone matrix. So, this is the first step in forming new bone. It’s soft tissue.
Over time, then, due to the unique capabilities of these cells, that unmineralized soft tissue slowly becomes mineralized. So, those bone-forming cells create that matrix fairly quickly in a matter of a week or 10 days. But, then, it takes two to three months for that new tissue to actually become, then, mineralized, so minerals start getting laid down in certain hydroxyapatite crystals. Then, say, you have a large mineral content eventually in what was originally soft tissue. That’s how we form new bone tissue.
There are some slightly different processes in toddlers and young children in terms of rapid growth of bone and length of bone, but the same basic process still holds – that you’re laying down this bone matrix and, then, it eventually gets mineralized.
So, later when we go in and measure bone density, what the machines are really measuring is the amount of mineral in the bone. That’s a good surrogate for the total bone mass, because there’s usually a constant fraction of the total tissue that’s mineral. So, it’s a good surrogate measure for how much bone you have. So, what we get measured at the clinic with a dual-energy X-ray absorptiometry, or DEXA for short, is bone density as a surrogate for total bone mass, and it’s also a surrogate for bone strength.
Bone’s main function–so I’m a physiologist. I study function. Its main function is to provide support for muscles and protection for critical organs, but its key attribute that we rely on is it will resist breaking. So, resistance to fracture is another way of talking about bone strength. I hope that answers your question.
Kathy Smith: It does answer my question. It also prompts some other questions about that. Just so I’m clear about it: we have these bones. Even though we think about them as hard and lifeless, they’re actually these living tissues with a blood supply, and we’re constantly breaking down the bone and, then, adding to it. So, there’s a constant ebb and flow of minerals going in and out.
Susan Bloomfield: You’re right.
Kathy Smith: Then, also, the minerals, I’m assuming–because we hear so much about it–it’s the calcium, and I know calcium phosphate and calcium carbonate. I also know that there’s collagen and maybe protein, but why don’t we just talk a little bit about how do we, then, maintain this bone density and keep it as maximum–now, I know that and what I’ve talked about–I was actually on the Oprah show many years ago when I wrote a book on menopause. One of the things I talked about there was this bank account – your bone bank account.
In your bone bank account, we want to start depositing in that account at an early age. We don’t want to wait until we’re menopausal to start thinking about our bone but start depositing. The way that we deposit in the bone bank account is through diet, it’s through exercise, it’s through watching stress, it’s through getting enough sleep.
As we start to move through life, let’s just talk about what is causing so many women over the age of 50 to have these diagnosis of osteopenia, which is that step before osteoporosis? I know that so many of my friends and people on Facebook are reaching out. It’s like, “I just got the diagnosis.” Why do you think this is happening?
Susan Bloomfield: You’ve asked a lot of questions there, rolled into one. If I may, I should have included this in the earlier answer. But you brought up this issue of bone balance or how do we maintain a certain bone density over time? If I may, let me introduce just one other bone cell type that’s real important to this discussion. Those are the bone resorbing cells – the cells that break down bone. They’re called osteoclasts, and these cells are responsible for starting what we call a remodeling cycle. They’ll come in and resorb – break down – just a tiny, minute amount of bone. Later, those bone-forming cells arrive to the same spot and re-fill in with new bone. That’s how bone tissue is constantly renewed and maintained and even minute, what we call microfractures, that accumulate in bone might be repaired. But that’s how bone stays healthy over time.
Then, at the larger scale, when we measure bone density, as long as that resorption of bone is followed by an equivalent amount of new bone formed, we’re in bone balance. You wouldn’t see a change in bone density.
So, once you reach the age of about 20, you’ve finished most of your growth, so your total bone mass should now be stable for a number of years. But you’re exactly right when you talk about that bone bank account. We are all paying into that account during our growing years but also between roughly the ages of 20 and 35. So, bone density and total bone mass tends to be fairly stable, assuming good health overall and reasonably good nutrition.
Starting anywhere between the ages of 30 and 35, all of us start losing minute amounts of bone mass with each successive year. We might be talking a fraction of a percent, but everybody hits some point where they start losing bone density year to year – minute amounts. Most of those will make absolutely no difference to the bone strength and resistance to fracture or your risk of incurring a fracture until you’ve accumulated at least probably, I’m just going say, in the range of 15% loss. So, that takes many, many year.
The rate of that loss is highly variable. In other words, our lifestyle factors as well as our genetics might have an impact on the rate of loss from that bone bank account. The physiologists call it peak bone mass: the highest value each person reaches, let’s say at age 35, for the sake of argument. Once you’ve reached that peak bone mass, now the aging process is taking over, and you’re losing a tiny amount year to year.
Now, the reason women at the time of year or just at menopause start getting this diagnosis of osteopenia, which is moderate bone loss. It’s nothing truly serious yet, but it’s a harbinger. It’s the first sign that you’re dipping into those lower ranges of bone density and bone mass. They’re typically seeing that change because they’re now, also, incurring another very important biological change, which is a significant drop in circulating estrogen values. That’s the main female reproductive hormone produced by the ovaries.
So, as ovarian function starts to shut down at menopause, serum estrogen – blood estrogen levels – are falling. Normal hormonal levels are one of the three key factors supporting great bone health. When estrogen values drop, estrogen basically takes the brakes off those bone resorbing cells, those osteoclasts, and you’ll see a spurt, an increase in bone resorption activity for a couple of years, and you’ll actually see accelerated bone loss compared to the normal age-related rate of loss.
Many women–not all–but many women in their early 50s will get that first report. “You’re a little bit below average on your bone density. We should keep an eye on it.” So, let me pause there and see if I’m headed in the right direction, where you would like to take this further.
Kathy Smith: I think you’re going in a perfect direction, because it’s like a thriller novel or something. You have me at the edge of the seat. You’re absolutely right. Most women do get that initial osteopenia and it’s, “Eek, what do I do now?” So, why don’t you continue?
Susan Bloomfield: Alright, so, I mentioned that normal hormonal levels – normal as defined by young adult levels – are one of kind of three key pillars that support optimal bone health. In fact, this harks back to a model that a nutrition colleague of mine – a very famous fellow in the area of calcium intake and bone health named Robert Haney. He worked most of his career at Creighton University in Omaha, Nebraska. He had a great model. He drew a three-legged stool and said for optimal bone health, you have to have each of these three legs in place. One is those normal hormonal levels. Second is good dietary intake, including adequate calcium intake. Third was physical activity.
Each one of those factors is, by itself, important to bone health. We say it’s necessary but not sufficient by itself to maintain optimal bone health. So, you need all three of those in place to optimize your bone density and, therefore, you’re minimizing your risk of fracture.
When women hit menopause, unless they go on hormone replacement therapy, which of course, then, boosts blood estrogen levels, they are incurring a weakening of that one leg. They’re hormonal levels are declining – a key hormone that supports optimal bone health. Now, not all is lost. All of us women over 50 are incurring this, and we’re not all fracturing bones two years later. It also takes a traumatic event: a fall or so forth. But some of us, genetically, are more susceptible to the more rapid bone loss, especially with that estrogen decline.
Then, of course, the question comes: that’s someone inevitable. We lose normal circulating levels of estrogen. Now, what do we do? Well, one answer for some women, if appropriate, as judged by their own physician, is a short-term course of hormone replacement therapy. Given all the press, however, about 10 years ago about some of the negative effects of hormone replacement therapy, that has become a less popular option for most folks. And very few women are on hormone replacement therapy for decades. And most of us hope to live for decades after 50, so then, the alternatives become first, let’s consider lifestyle factors. Let’s make sure your diet is optimal, that you’re getting at least–for post-menopausal women, I believe the recommendation is now 1200 milligrams per day if not 1500 milligrams of calcium per day. That’s one and a half grams.
Another factor that is less well-publicized, I believe, in the medical community is the fact that you also need adequate protein intake. There are a number of women who, particularly if you’re into any kind of cyclic weight loss, if you’re constantly dieting, reducing energy intake alone can produce some bone loss, concurrent with losing body weight. But also having adequate protein intake has been shown to be important. Because if you’re protein intake is low, it tends to produce some hormonal changes that, then, drive a little more bone loss. So, the optimal diet is something that contains at least 1500 milligrams of calcium a day but, also, adequate protein and energy intake.
Short-term dieting is ok. I don’t mean to throw a panic into folks who are on weight-loss diets. Sometimes that’s the best thing they might be doing for their overall health. But prolonged dieting, particularly severe dieting, can itself impact on bone density. That’s a brief summary of the nutritional component.
Kathy Smith: Can I jump in before we go to my favorite topic, which will be exercise, I’m sure–before we jump over there. With the nutrition, the one thing I do want to throw out there is that we think about calcium and we think about milk and yogurt. But I want to put it out there that there’s a lot of places to get calcium and one thing that I make sure that every day I’m getting the darker greens and even things like kale, bok choy, turnip greens, almond butter. I do an almond butter in the afternoon. That has calcium in it. You have other areas where you can start looking for, including figs.
So, you can go online, you can google it for just sources of calcium and just to start incorporating other foods that you might not be eating right now, especially because a lot of people through the years have started cutting out milk products for various reasons and dairy. So, even if you’re drinking the almond milks or the soy milks, a lot of those have been fortified at this point. Just to bear in mind about the sources of calcium.
Any other thoughts on actually food that we’re eating? I know we talk about calcium a lot and we talked about it today a lot. That’s the biggy that gets the most news but, then, there are other minerals that help support bone health. Do you want to address that just for a minute?
Susan Bloomfield: I’m less expert in that area, but I can tell you that I do know if you are eating a reasonably balanced diet and getting your fruit and vegetable intake as advised by the RDI, as I think they are now, you will be getting enough of those other trace minerals to support good bone health.
The tough one is calcium, because the 1500 milligram mark a day is tough to get, especially if you don’t eat dairy. I do believe there is a role–especially for those if you can’t eat dairy. In fact, I take a calcium supplement every day myself even though I regularly drink milk, because it’s really hard to get up to that 1500 milligram amount. So, there’s a role for calcium supplements, I believe, unless you’re eating a whole lot of dairy. Getting that amount of calcium from the very good food sources you mentioned earlier will take a phenomenal volume of those. So, I think there’s a role for the calcium supplements.
I’m sorry, I can’t site from memory the exact amounts of–there’s manganese, there’s zinc and a few other trace minerals that support bone health. But, again, if you’re eating a reasonably well-balanced diet, particularly with vegetables and fruits, I think you’re covered.
Vegetarians might need to consult with a dietician or what’s available online. You’re missing a few minerals that you might get in red meat, for example, if you’re not eating red meat. But, again, a reasonably well-balanced diet I think you’ll be fine.
Kathy Smith: Well, then, let’s switch to exercise. I know strength training and lifting weights has been shown to be one of the best ways to maintain bone density throughout your entire body. But I was just reading an article in the New York Times, and it was about some of the latest research on having the amount of G-force or the amount of impact that you have on your bones. I think it’s important to delve into this, because I know a lot of articles around, a lot of doctors when they talk about–even a friend of mine who was staying with me a few weeks ago when she got the diagnosis of osteopenia, the doctor said, “You just need to exercise.” The question was, “Do you exercise?”
She said, “Yes.”
And I said, when she got off the phone, I mentioned, “You do a bar class,” which is great, and it’s good exercise. But at the same time, there’s not a lot of impact with it. So, can we talk about this idea of G-force and how much do we need to stimulate bone density?
Susan Bloomfield: I’m trying to think of the best way to summarize this quickly. There’s two major mechanisms, two major methods by which exercise impacts on bone. Here’s the key thing to understand that will help unify this. The stimulus to bone to maintain optimal bone formation and bone balance is actually the deformation of the bone. In other words, it’s a physical tension or even minute bending on the bone that is the stimulus to keep forming new bone. So, it’s not like a heartrate we use to indicate aerobic exercise intensity.
For bone, if you have any engineers in the audience, they’ll know the phrase “strain on bone”. It’s just a measure of a minute deformation of a material. That’s the stimulus. That’s the important thing to incur. So, if you keep that in your mind in the background, then you can understand that we can generate those deformation forces on bone in several ways.
One is, as you’ve indicated, by generating these G-forces. In other words, in lay language, it’s just impact. If you jump from a step – thinking back to the old aerobics classes or step aerobics, where you’re up and down and up and down all the time – and any time you land–think of a volleyball player for example jumping and landing, jumping and landing. Basketball players, they incur a lots of impact forces from all that jumping. A lot of studies have been done in kids showing that jumping or jumping rope or so forth even for 10 minutes a day can have very dramatic impact on forming new bone, gaining bone density.
Now, remember, kids are way more plastic than those of us over 50, but that does seem to be one key easy way to generate those forces on bone. Now, that said, I’m not going to come out and promote jumping exercise for your average person over 50. A lot of us accumulate sore joints. Arthritis becomes an issue. Other limitations: balance. Impact forces are great, and if you’re healthy and have great joints, more power to you.
Running is a very simple example. Every time you land on that foot, you’re generating maybe two to four times your body weight in G-forces. That’s great. But running’s not for everybody. I haven’t been able to run since I was 30, because of bad knees. So, it’s not always an option for everyone.
The other main way of generating that tension on bone is higher-force muscle contractions. In other words, not just easy stretching or slow walking but more vigorous activity. So, the stronger a contraction the muscle generates, the more tension it puts on the bone it’s attached to. So, that’s the background behind why we think activities like weight training are so – in general – beneficial to maintaining bone density.
Now, that said, it’s very, very important for your listeners to hear that any exercise is way better than no exercise. For example, I myself, am a swimmer. I still compete in master swimming. I will do workouts in the water in a non-weightbearing environment. So, I’m generating almost zero G-forces on my bones except when I do maybe a flip turn at the end of the lane. But I am, especially if I’m doing some higher intensity sets, generating some higher force muscle contractions on some bones.
I also do weight training because I know that swimming in a non-weightbearing environment is not optimal. In fact, adding in walking, I have the privilege of working on an academic campus. I get to get outside and walk a fair amount each day, getting to meetings. That’s also beneficial. So, just because walking doesn’t generate the high G-forces that running does, it’s still way better than no activity at all.
So, if I could summarize this briefly, you can generate, yes, jumping or stepping activities and/or running that generate higher G-forces are great if your joint health will allow. But if you have arthritis and/or any issues with balance, that may not be the safest mode of exercise for you. So, getting out and walking as briskly as you can or engaging in other exercise where–it’s optimal if you can get some higher intensity spurts in. You may have read about the latest vogue is high-intensity interval training and its value for everyone especially for metabolic health, muscle health, but it can also, I think, be beneficial for bone health.
Kathy Smith: Well, it’s one of the reasons why I throw in a couple of workouts a week of total body, strength training workout. Because as you said, wherever you’re placing that tension, that force, those are the bones that are going to get the most benefit. So, when we’re doing upper body, when I’m doing shoulder presses whatever, you’re stimulating more of that growth in that part of the spine. When you’re doing more of the lower squatting, lunges, whatever, you’re stimulating the bone growth and lower part of it. So, I think for anybody out there, if you’re swimming, if you’re walking, if you can run, great, but also get into the gym a couple of times a week if possible.
I know it’s almost time to go. I’d love to just ask one more question. A lot of people on Facebook were asking about the pharmaceuticals, the drugs. Do you have any? I know it’s a big story and we don’t have a lot of time to cover the whole story, but do you find them beneficial? Would you recommend women start on a prescription drug if needed?
Susan Bloomfield: I can tell you there’s certainly a place for some of these pharmaceutical treatments, particularly for those individuals who either by genetics or lifestyle factors are finding that, yes, my bone density is not only in the osteopenic but maybe the osteoporosis range. So, once it declines enough, you may get that diagnosis of osteoporosis.
It’s critical that people work with their physician, because each person’s different. They have different risk factors, and we well know that each medication, each pharmaceutical treatment comes with certain risks and benefits, and they are not always appropriate for every person. But I do think there is a role for these pharmaceutical agents, and more and more of them are coming out each year.
One major category is what we call the bisphosphonates. Those were the first drugs approved back in the mid-90s I think. Alendronate, or Fosamax, is one of the most commonly used ones, one of the first to be patented and approved by the FDA. They have shown pretty good efficacy in both halting bone loss and in some cases a small, absolute gain in bone density.
Each of these agents comes with some risks, and there are certain populations who should not take them based on their medical background. There are other categories that block or that mimic the actions of estrogen without being hormone replacement therapy itself. Others act with different mechanisms to slow down the actions of those bone resorbing cells – osteoclasts. The biologists have gotten very smart on different strategies to slow their activity.
So, it really comes down to each person, and this includes men as well. Because men, particularly over 70, if they escape cardiovascular disease, are also at risk for bone loss. So, let’s not assume it’s just a women’s problem. But should check with their physician and say, “What are my options, and is it time for us to consider pharmaceutical therapy?” Because not everyone can exercise, not everyone can eat enough calcium, so it may be that that medication will provide a critical boost that’s needed. That’s a quick summary.
If I can add one final message, however, related to the exercise message, most of my career, I’ve focused on what happens with lack of exercise or with simulated space flight. We do know that one key thing to avoid is prolonged, non-weight bearing periods. In other words, the bone loss that healthy crew members on space station incur if they were doing no countermeasures – which they are – with diet and exercise. If they have no interventions, they can lose bone at a ten-fold faster rate than a healthy post-menopausal woman would. So, that total unloading.
For example, if you’re in bed for a prolonged illness, it’s very, very helpful if you can get and stand up and walk even five/ten minutes a day. You really want to minimize that total lack of weight bearing. So, prolonged bed rest is sometimes necessary, but try to minimize it to an absolute minimum, because we do know that the total lack of weight bearing is really deleterious to your bone health.
Kathy Smith: Does that include prolonged sitting?
Susan Bloomfield: To a point. But most of us sit at work all day, right? As long as you’re getting up and walking for some part of the day, you’re probably ok. It’s the total lack of weight bearing that just really activates bone absorption and a much more rapid rate of bone loss. For most people, I’m going to take a stab, if they’re walking at least three to five thousand steps a day, you’re probably fine. It doesn’t even have to be high intensity. But taking it all away – no weight bearing at all – is what we know for sure is a killer for maintaining optimal bone density.
Kathy Smith: Fantastic. My big take-away today was this image that you gave us of this stool or that tripod, where you have your hormones and you have your exercise and you have your diet. The hormones at one point, unless you are going to venture into hormone replacement, you’re not as in control of.
The other two you can. You can start shifting your lifestyle. And I think for most of us, it’s that adding some more strength training as well as some higher impact if you can. Then, making sure you’re getting enough calcium. As you mentioned, it might be that calcium supplement that most of us are going to need.
Susan Bloomfield: Yep.
Kathy Smith: On that note, thank you so much. It sounds like something’s happening over there. Are you brushing your teeth?
Susan Bloomfield: Sorry. No. Just cleaning up a little here while we’re finishing up. Sorry that came through on the mic.
Kathy Smith: That’s ok. It doesn’t matter. I love it. Multitasking, that’s maintaining good bones. Susan, thank you so much. You’ve been so incredibly helpful. I’m sure we’re going to be getting such a great response on this, because it’s a topic that people are very confused about, so thanks for clarifying.
Susan Bloomfield: Great. Well, it’s my pleasure. Thanks for the invitation.
Kathy Smith: Bye now. Have a great day.