Bad for bones? The latest on food and fractures.
An apple. A bagel. A chunk of cheese. Which of them may weaken your bones and muscles, boosting your long-term risk of hip or spinal fractures?
It's no surprise that calcium-rich cheese should help strengthen your bones (though that may not happen if you get too little vitamin D).
But recent studies also suggest that too many grain foods--bagels, bread, cereal, rice, pasta, and cookies and other baked goods--may lead to bone and muscle loss by creating an acid load in the body.
The good news: Replacing grains with fruits and vegetables can neutralize the acid load (and maybe some of that blubber load you've been trying to jettison).
Here's the latest on what we know about what may--and may not--keep you fracture-free.
One in two women and one in four men over age 50 will break a bone because of osteoporosis, which literally means "porous bones." The older you are, the higher your risk.
By the time you're 40, your body starts losing more bone than it makes. Losing just 10 percent of your bone mass can double your risk of fracturing a spine or hip.
And it's not just weak bones, but weak muscles, that lead to debilitating fractures. Here's how to avoid both.
Q: What would surprise people who want to prevent bone fractures?
A: You can't just think about bones. As we age, we lose muscle mass at a pretty good clip and our balance becomes worse, so we have a greater risk of falling. This is a major, major contributor to osteoporotic fractures.
Falls create the fracture opportunity, so there's a lot of interest in them these days. For five years now, we've viewed fracture risk as not just a matter of bone content, but also a matter of muscle.
If you can't improve muscle performance and balance, it's hard to lower the risk of fails, and falls will create fractures. So we're interested in nutrients that affect both bone and muscle.
Q: Which nutrients affect both?
A: The acid-base balance of the diet is one factor that we're working on enthusiastically. The acid load generated by many diets isn't handled well by older people because of their declining kidney function. So they become gradually, mildly, but progressively acidotic. That is, they have too much acid in the bloodstream.
That causes muscle wasting. Muscle loss is the body's way of adapting to the excess acid. So is bone loss.
Q: So the body breaks down bone and muscle to neutralize the excess acid?
A: Yes. We know that bone cells have hydrogen ion receptors, so they're sensitive to excess acid. No one has worked out exactly how acid signals the muscle to break down. But it's clear that the body tries to defend against increasing acid by breaking down bone and muscle.
Q: Do acidic foods like citrus fruit create acid in the body?
A: No. Grains--like bread, cereal, rice, pasta, crackers, tortillas, cookies, doughnuts, cupcakes, and similar foods--and protein do. When they are metabolized, they release sulfuric and other acids into the bloodstream.
In contrast, fruits and vegetables get broken down into bicarbonate when they are metabolized, so they add alkali to the body. And that helps to neutralize acid. Sugars and fats are generally neutral. So when the diet is relatively poor in fruits and vegetables relative to grains and protein, that's a net acid-producing diet. [See "Dropping Acid," p. 5.]
Q: Do we have conclusive evidence that eating a diet that neutralizes excess acid protects bone?
A: No, but it's promising. We've put people on an acid-producing diet--that is, a diet high in protein and grains--and then given them an alkali like potassium bicarbonate. And you can see markers of bone turnover drop. And nitrogen excretion, which is an indication of muscle wasting, also declines.
These effects occur immediately, and they're reversible when you reverse the acid load. That's been shown in short-term studies, and we also did a three-month study in 170 healthy older people.
When we gave bicarbonate to the people on the acid-producing diet, it resulted in reduced bone turnover markers. And the women--who got a higher dose for their body weight than the men--actually improved their performance doing a double leg press. The bicarbonate increased power in their legs and decreased nitrogen wasting, which suggests that they were losing less muscle mass.
Q: Were the people very old?
A: No. We studied men and women aged 50 and older. The average age was 63. Muscle wasting picks up and is continuous from the 40s on. You can see this if you look around you. You can see it in the mirror. And you can also see it on the street. It's obvious. You see people with a big belly and skinny legs.
Q: Do both animal and vegetable protein produce acid?
A: Since plant protein generally comes in foods like beans, which have an accompanying alkaline source, it is less acid-producing than the same amount of protein from beef. But it's not the protein that matters.
The acid-producing quality depends on how many sulfur-containing amino acids are in the protein, and there's a wide range in both plant and animal protein sources. So it's misleading to refer to protein as plant or animal, unless you know the overall picture.
Q: Are you saying that protein is bad for bones?
A: No. Many adults aren't getting the amount of protein that most of us think is needed. The Recommended Dietary Allowance is 0.8 grams of protein per kilogram of body weight, but 1.0 or 1.1 grams per kilogram seems to be associated with slower muscle wasting in older people. There's not final proof, but the evidence is compelling.
So cutting protein to lower acid load can be counterproductive to individuals with marginal protein intake. Instead, we need to cut back on grain foods. In an obese population, to get rid of some of these grains--which are calorie-laden and acid-producing--would be the ticket.
Q: What's the next step in your research?
A: We want to do a longer, three-year trial, with hard endpoints like muscle size, muscle performance, rates of bone loss, etc. But first we need to make sure that we are using the optimal dose of potassium bicarbonate. We are trying to get a dose-ranging study approved and done so that we can do the big trial with the best dose.
Unfortunately, that isn't always done. With vitamin D, for example, trials have used different doses. There are no dose comparisons that would enable you to make an educated guess at the best dose. So now--millions and millions of dollars later--we are left trying to infer what the best vitamin D dose would be. It's wasteful to do it that way. But getting funding to test doses is so grindingly slow.
Q: Would you recommend that people consume bicarbonate?
A: No. I would advise people to eat fruits and vegetables. We're studying potassium bicarbonate because we know precisely how much acid it neutralizes.
Q: What other nutrients are linked to both muscle and bone?
A: Vitamin D. It improves strength in the legs and lowers the risk of falling. Second, it improves bone strength, so it lowers the risk of your having a fracture should you fall.
Q: How does it work?
A: Vitamin D is essential for the absorption of calcium, which is needed for bone. Animals that are totally vitamin-D-deficient cannot form bone and can't remodel bone. [See "Super Remodel," p. 6.] Inadequate D levels are associated with more rapid bone loss and more fractures, no question.
Q: How does vitamin D affect muscle?
A: That's not as thoroughly understood at the cellular and molecular level. There are vitamin D receptors in muscle tissue. And in a couple of small studies, treatment with D increased the number of vitamin D receptors and the size of the type 2 muscle cell fibers. And extreme vitamin-D-deficiency is associated with a deficit of the type 2 fibers.
These are the fast-twitch fibers that are your first responders when you are losing your balance. It is well documented that inadequate D levels are associated with higher risk of falling. So vitamin D is really important for muscle.
Q: Do most people get too little vitamin D?
A: Yes. Sixty percent of people in the U.S. and Europe get too little vitamin D. The percentages are higher in the Middle East and Southeast Asia.
The most important source of vitamin D is sun exposure, which increases the body's production of vitamin D. The diet is not rich in D. There's a little in fatty fish and in eggs, but by and large, most people without sun exposure will need a supplement.
Q: You were on the panel that set the current Recommended Dietary Allowances for vitamin D. Are the RDAs too low?
A: Yes, we still have the 1997 values--400 International Units for adults aged 51 to 70 and 600 IU for people over 70--and they are too low.
People aged 60 and older need 800 to 1,000 IU a day to keep blood levels at 30 nanograms per milliliter. But we'll just have to wait to see what the panel will do this time around.
Q: What if you're low in vitamin D and are producing too much acid?
A: In animal experiments, we're trying to determine the precise effects that both vitamin D and an acid load have on muscle at the cell level to see whether there is any interaction. It could be that vitamin D doesn't function well in an acid environment. That's our hypothesis. We'll have those results soon, and it's going to be very exciting. It might open some new avenues for research.
Q: What nutrients are crucial just for bane?
A: Calcium is huge. In meta-analyses, there's about a 20 percent reduction in the risk of fractures when people are given both calcium and vitamin D. We also found a lower risk of tooth loss when we have people over 65 take both calcium and vitamin D supplements for three years. However, calcium without vitamin D may not be as protective of bones or teeth.
Q: Does potassium matter?
A: We did a trial to figure out whether it was the potassium or the bicarbonate or if you needed the combination. And it turned out it was the bicarb. Potassium had no impact on short-term indicators of bone loss or muscle wasting. Potassium is great for other things like blood pressure.
Q: And vitamin K?
A: It was promising for a while, but vitamin K1--that's what's in lettuce and other dark leafy green vegetables--had no impact on rates of bone loss in three or four large trials. There is interest in some of the other K compounds but at higher, pharmacologic doses, not what you would get in foods.
Q: What about magnesium?
A: We haven't made much progress with magnesium, simply because it's so hard to get an indicator of the body's magnesium status. The blood level doesn't tell you that, and there's no easy assay to measure tissue levels. It's analogous to the osteoporosis field prior to bone-density scans. You couldn't get a handle on what the bones were doing in a large number of people.
Q: Does excess salt harm bones?
A: Salt--sodium chloride--isn't good because it causes calcium leaching. It can tip you into a calcium deficit if you have a borderline calcium intake and are eating a lot of salt. In order to get rid 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 fractures 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 Bottom Line."]
When there weren't many vitamin-D-fortified foods or supplements, some doctors were recommending a double daily dose of multivitamins in order to get the 800 IU of vitamin D that some of us recommend 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.
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, unequivocal 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 different signal to the bone.
Q: How does weight-bearing exercise strengthen hones?
A: This has been a big question for a long time. It appears that the mechanical load from the weight is turned into a chemical signal by the osteocytes. These are the former osteoblasts, the bone-forming cells, that get entrapped in the bone.
For years we had thought that, once they did their job, they were just entombed, 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.
Q: Are we treating the right people with drugs to prevent bone loss?
A: Not exactly. I led a group that looked 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 the World Health Organization to estimate the 10-year risk of a fracture based on age, weight, family history 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 medication?
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?
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 physicians are not recognizing the need for treatment.
So I'm hoping that this condition will be taken more seriously by physicians treating women and men in their 70s and 80s and 90s. And that they don't jump on the treatment bandwagon so early with people in their 50s.
Q: Should all women get their bone density measured?
A: Most don't need it until they're 65. Women under 65 should get a bone-density test and get a FRAX score only if the doctor is concerned about their risk factor profile.
Q: What about men?
A: Men can wait until age 70, but then the advice is the same. If their T-score is in the osteopenia range and their FRAX score is high enough, they're good candidates for treatment.
Q: The theme of this year's World Osteoporosis Day--October 20th--was "Don't miss the signs of a breaking spine." Why do spinal fractures often go undiagnosed?
A: Sometimes the fractures are slow and occur micron by micron. Nerve endings aren't that involved. People will notice that the shape of their back or their height has changed, and they'll get an X-ray and see these fractures. That's not uncommon.
But they would not have been painful discrete events, They don't hurt, That's fortunate, but unfortunately, the intervention is sometimes delayed because people are unaware of them.
Q: Are hip fractures a bigger problem?
A: Oh yes, because they require surgery and longer hospital stays and then more time in a rehab institution, etc. Hip fractures cost about $30,000 each in direct medical costs.
But spinal fractures are also associated with increased risk of declining health and death. That's even true for wrist fractures. A recent study found that people who've had wrist fractures start to lose their overall ability to get around and do their activities over the following six to seven years. It's an indicator of declining health.
Q: Are hip and spinal fractures equally preventable?
A: With diet and exercise, yes. With drugs, it depends. Some drugs lower risk of spine fracture only, whereas others lower risk of fractures at all sites.
Bisphosphonates like Fosomax, Actonel, and Reclast--the once-a-year injection--have powerful effects on the spine and hips. Drugs like Evista and some of the weaker bisphosphonates, like Boniva, just lower spine fractures.
Q: Can bisphosphonates cause hip fracture?
A: There may be a slight increase in the risk of an unusual kind of hip fracture, but it pales beside the risk of having a fracture from untreated osteoporosis. We need to keep it in perspective.
It's similar to the fear that the bisphosphonates could cause jaw osteonecrosis--a rare condition involving bone lesions that fail to heal. In both cases, the risk is minuscule compared with the risk of not treating osteoporosis.
Q: But there's quite a bit we can do before drugs are on the table?
A: Yes. The take-home message is that diet and exercise have real impact on both bone and muscle health.
WHAT'S YOUR FRAX?
You can use the FRAX (Fracture Risk Assessment Tool) to estimate your risk of fracture, whether or not you've had your bone mineral density (BMD) tested. The National Osteoporosis Foundation Guide recommends that doctors consider prescribing medication if your risk of a hip fracture is at least 3 percent--or your risk of any major bone fracture is at least 20 percent--over the next 10 years. Most women (and men) do not cross either of those thresholds until their 70s.
A typical 65-year-old woman--like Wanda B. Strong--would need medication only if she had a previous fracture due to mild trauma (like falling from standing height, not as the result of a car crash), or if she had taken glucocorticoids (like prednisolone) for more than three months, or if she had rheumatoid arthritis (not osteoarthritis), or if she had secondary osteoporosis (a condition--like menopause before age 45 or Type 1 diabetes--that is strongly linked to osteoporosis).
To calculate your FRAX score, go to www.sheffield.ac.uk/FRAX and click on Calculation Tool.
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.
2. Osteoclasts use enzymes to dissolve bone tissue.
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.
STEP ON IT!
Any weight-bearing exercise is good for your bones. Here are a few high- and low-impact examples. Exercise that isn't weight-bearing may be good for your heart and waistline, but won't help your bones.
Jogging or Running
Using elliptical training machines
Using stair-step machines
Fast walking on a treadmill or outside
Bicycling or Indoor cycling
Stretching and flexibility exercises
Bess Dawson-Hughes is a professor of medicine at Tufts University School of Medicine in Boston and the director of the Bone Metabolism Laboratory at the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts. She is a past-president and trustee of the National Osteoporosis Foundation, general secretary of the International Osteoporosis Foundation, and the author of more than 280 journal articles, book chapters, and reviews. Nutrition Action's Bonnie Liebman spoke to her by phone from Boston.
DROPPING ACID Here's the potential renal acid load (PRAL) "for a sample of foods. Look for foods with high negative PRALs (like fruits and vegetables) to neutralize high positive PRALs. Why list only whole milk and full-fat yogurt? You'd have to ask the German researchers who compiled the data in the 1990s. Fruits PRAL Raisins (1/4 cup) -8.4 Apricots (4) -6.7 Kiwi fruit (2) -6.1 Watermelon (2 cups) -5.3 Pear (1) -4.8 Orange (1) -4.2 Apple (1) -3.4 Pineapple or Strawberries (2/3 cup) -3.1 Peach (1) -2.4 Vegetables (1/2 cup cooked unless noted) Spinach -12.6 Zucchini -4.1 Carrot -3.8 Tomato, raw (1) -2.6 Cauliflower -2.5 Lettuce, raw (3 cups) -2.1 Green beans -1.6 Broccoli -0.9 Asparagus -0.4 Miscellaneous Olive oil (1 Tbs.) 0.0 Sugar (1 tsp.) 0.0 Butter (1 Tbs.) 0.1 Milk chocolate (1.5 oz.) 1.0 Cereal & Grains Bread, whole wheat (1 slice) 0.8 Bread, white (1 slice) 1.6 Rice, white (1/2 cup cooked) 2.7 Rolled oats (1 cup cooked) 8.7 Dairy & Eggs Ice cream, vanilla (1 cup) 0.8 Soft cheese (1 oz.) 1.2 Whole milk (8 oz.) 1.7 Fruit yogurt, whole milk (6 oz.) 2.0 Eggs (1 large) 4.1 Hard cheese (1 oz.) 5.4 Cottage cheese (1/2 cup) 9.6 Fish, Meat, & Poultry (5 oz. raw) Haddock 9.7 Beef or Pork, lean only 11.2 Chicken, no skin 12.4 Turkey, no skin 14.1 Beverages Red wine (5 oz.) -3.5 White wine, dry (5 oz.) -1.8 Draft beer (16 oz.) -1.0 Coca-Cola (12 oz.) 1.5 Source: J. Am. Diet. Assoc. 95: 791, 1995. THE BOTTOM LINE Shoot for This Much Food or Nutrient Every Day What You Need to Know Calcium 1,000 mg if 19 to 50 To protect the prostate, 1,200 mg if over 50 men shouldn't exceed 1,500 mg a day. Vitamin D 400 IU if adult up Adults 60 and younger to age 60 may need more than 400 800 to 1,000 IU IU a day, but evidence if over 60 is hard to come by because fractures are rare in younger people. Protein At least 60 grams These levels are for a (women) typical 130 lb. woman or At least 80 grams 175 lb. man. Rule of (men) thumb: Your target protein in grams is roughly half your weight in pounds. Fruits & Vegetables At least 11 servings There's no better way to a day neutralize excess acid. Exercise 30 minutes or more To get or stay trim, (weight-bearing) you'll need 60 to 90 minutes a day. Vitamin A retinol 2,330 IU (women) The outdated Daily Value (as acetate or 3,000 IU (men) (DV) for vitamin A palmitate) (More is okay that's used on labels only if it's from (5,000 IU) is too high. beta-carotene.)