Ms. Colberg is an exercise physiologist and associate professor of exercise science at Old Dominion University in Norfolk, Virginia. A diabetes researcher with almost four decades of practical experience as a type 1 diabetic exerciser, she is a Fellow of the American College of Sports Medicine, a professional member of the American Diabetes Association, and the author of three books on diabetes.

Editor's Note: You wouldn't buy a house without checking the foundation and support structures to make sure they are sound, so you already know why keeping your bones healthy is so important. As you age, you have to do more to offset the bone loss that begins as early as age 25.

The following is an excerpt from a new book by The Doctor's Senior Living specialist, gerontologist, Dr. John Morley: The Science of Staying Young, 10 Simple Steps to Feeling Younger than You Are in 6 Months or Less, written with Sheri R. Colberg, Ph.D. (McGraw-Hill, 2008). Used by permission.

Healthy bones and joints are crucial to your mobility and extended youthfulness, as well as living a pain-free life as you move around. Some largely effective strategies exist to prevent and limit potential bone problems, no matter what your age is, including adequate calcium and vitamin D intake, regular weight-bearing exercises, avoidance of phosphorus-filled sodas, moderation of protein intake, and in some cases hormone replacement therapies. All of these options for improving bone health will be addressed in this [article], along with how to maintain healthy joints in order to reduce and minimize pain from any arthritis you may develop to help you stay feeling younger than your chronological age.

Thinning Bones: Risk, Screening, Prevention, and Treatment
Unfortunately, everyone is experiencing slow bone demineralization throughout adulthood starting around the age of 25, which can eventually lead to fractures and a lower quality of health. This process, known as osteoporosis, can lead to a greater incidence of fractures, especially of your hip, wrist, or spine, at whatever age you finally reach a critical minimum bone density. According to the National Osteoporosis Foundation, 50 percent of women and 25 percent of men over 50 will have an osteoporotic fracture in their lifetime. Moreover, the Surgeon General's report issued in 2004 predicted that by 2020 half of all Americans age 50 and over will have weak bones without significant changes to the nation's diet and lifestyle as a whole. At present, an estimated 10 million Americans — 80 percent of them female — already have this disease, and another 34 million have significantly reduced bone mass (a condition known as osteopenia). Thus, it's not a problem to be ignored if you want to live long and well.

The term "osteoporosis" was originally coined in the early 19th century, but it wasn't until 1940 that the loss of estrogen in women at menopause was identified as playing a role in its development. It has often been asserted that osteoporosis is actually a pediatric disease because the amount of calcium you ingest during your childhood likely is a major determinant of your bone mineral density later in life. Regardless of when it actually starts, it's undeniably a chronic condition that causes bones to gradually lose their stored calcium, leaving them porous and brittle. Over time, this process of demineralization causes the skeleton to become weaker, and when it reaches a critically low level, bone fractures can occur and recur from seemingly minor impacts.

[O]steoporosis is actually a pediatric disease because the amount of calcium you ingest during your childhood likely is a major determinant of your bone mineral density later in life.

Whereas bone loss occurs over many years, you will likely only become aware of having this condition when fractures are blatant or postural changes are well advanced. For example, repeated, undetected compression fractures in the vertebrae of the spine can lead to stooped posture and backaches, both of which are common characteristics of older women (and some men). Hip fractures resulting from this disease can be immensely debilitating, often signaling the start of a downward trend of reduced strength and a lower quality of life.

Who Is at Risk for Osteoporosis?
Certain immutable factors increase your risk of developing osteoporosis. Among them are small frame size, female sex, age, hereditary factors, Caucasian or Asian race, early menopause, prolonged immobilization, low levels of estrogen or testosterone, excess thyroid hormones (e.g., overactive thyroid gland), and extended steroid use (such as prednisone). Other contributory behaviors like cigarette smoking, excessive alcohol consumption, physical inactivity, and inadequate intake of calcium and vitamin D can be controlled and modified to lower risk.

Women have an inherently greater risk for osteoporosis than men because men's skeletons contain a larger reserve of bone minerals, but also due to faster rates of loss in females. After menopause, women lose bone at an average rate of two to three percent per year, while men of a similar age are losing only 0.4 percent annually. The most visible sign of this bone loss is a gradual shortening in overall height over time. In Caucasian and Asian women in particular, bone mass starts to decrease in the femur (thigh bone) in their mid-20s, followed by spine losses in their mid- to late-30s, and arm bone demineralization after 40 years of age.

Screening for Osteoporosis
Due to recent advances in the way bone density is measured, it's now easier than ever to find out if you have already significant bone loss, if you're pre-osteoporotic (i.e., you have osteopenia), or even if you're at risk for osteoporosis in the future. Testing methods include single-photon absorptiometry (SPA), dual-photon absorptiometry (DPA), dual-energy X-ray absorptiometry (DEXA), computed tomography (CT) scanning, and ultrasound. If you have already suffered a bone fracture of the wrist, back, or hip seen on X-ray, you don't need to have a special test done before being treated for osteoporosis; it's assumed that you already have it.

All women reaching the age of menopause should have their bone mineral density measured, along with at least one more check at 65 years of age. Since they lag behind, men should ideally have testing done when they reach 65 to 70 years old. The actual diagnosis of osteoporosis is made when you have a bone mineral density that is more than 2.5 standard deviations below the young adult average (a T-score of 1.0 to 2.5). Your bone mineral density should be repeated after two years to determine your rate of bone loss, and the testing should always be repeated at the same time of year, as seasonal changes in bone density are common.

Prevent Bone Loss and Strengthen Your Bones
The best preventive measure is to start out with the highest peak bone mineral density that you possibly can in your mid-20s. The rate of loss of bone minerals is fairly steady over time, so having denser bones at your peak will allow you to live longer without reaching a critical osteoporotic fracture level. Preventive strategies include appropriate exercise, adequate calcium intake, dietary modifications, and boosting vitamin D levels. There are also steps you can take now to improve your current bone health, even if the process can't be completely reversed. Finally, you may want to consider hormone replacement therapies or other medications to ensure that your bones stay healthy throughout your lifetime.

Appropriate Exercise for Bone Health
Whether or not you have osteoporosis, it's advisable for you to begin a program of moderate, weight-bearing exercise, especially if you don't already exercise regularly. These exercises include walking and aerobics, and they strengthen bone while increasing bone forming processes. In addition, most types of resistance or weight training positively stress bones and result in calcium phosphate deposition, resulting in thicker, healthier bones. Studies on women with significant osteoporosis engaging in resistance training for a year have shown a small, but measurable, increase in bone mineral density; conversely, their similarly-aged, non-exercising peers experienced a decline in their bone thickness over the same time period. So, even if you can't completely reverse the thinning process, you can certainly slow it down significantly or even stop it in its tracks for a time.

Taking in Enough Calcium
Women in the United States consume an average of only 500 milligrams of calcium per day, which is less than half the recommended daily allowance for younger adults. Adequate calcium intake from childhood through your mid-30s is crucial to the development of the greatest possible deposits of calcium phosphate salts in bone. It's less certain whether adding calcium to your diet after menopause can prevent bone loss; however, women who consume large amounts of calcium experience fewer hip fractures. Thus, most doctors recommend that adult women and men consume between 1,000 and 1,200 milligrams of calcium per day, with the higher intake recommended for postmenopausal women over 50 years old not taking estrogen and everyone over the age of 65.

If you avoid milk because of lactose intolerance, the most reliable way to get calcium is to choose lactose-reduced or low-lactose alternative dairy products.

Calcium supplements are certainly one way to ensure adequate intake, but it can also be accomplished through intake of calcium-rich foods (Table 1), which is the preferred method as it can convey other health benefits as well. According to most nutritionists, the best choices are low- or non-fat dairy products. If you avoid milk because of lactose intolerance, the most reliable way to get calcium is to choose lactose-reduced or low-lactose alternative dairy products, such as cheese, yogurt, or lactase-treated milk, or to consume the enzyme lactase before consuming milk products to aid digestion.

On the other hand, others and particularly vegans (complete vegetarians) would argue that many green vegetables have calcium absorption rates of more than 50 percent, compared with about 32 percent for milk, making vegetables a potentially better source. A recent article in the American Journal of Clinical Nutrition reported calcium absorption to be about 53 percent for broccoli, 64 percent for Brussels sprouts, 58 percent for mustard greens, 52 percent for turnip greens, and 40 to 59 percent for kale. Likewise, beans (e.g., pinto beans, black-eyed peas, and navy beans) and bean products, such as tofu, are rich in calcium. About 36 to 38 percent of the calcium in calcium-fortified orange juice is absorbed (as reported by manufacturer's data). Even most fruits contain some calcium, albeit relatively small amounts, as do most nuts and seeds. However, the amount of calcium that can be absorbed from these foods varies, so both calcium content and its bioavailability, shown in Table 1, should be considered. Some plant foods have calcium that is well absorbed, but low in total content per serving.

Table 1
Food Sources and Absorption Rates of Calcium.
Food Source Calcium Content (milligrams) Fractional Absorption (%)
Cow's milk, 1 cup 250-300 32
Most cheeses, 1.5 ounces 305-336 32
Yogurt, low-fat, 8-oz container 338-448 32
Soymilk, calcium fortified, 1 cup 75-300 24
Tofu, medium or firm, 1/2 cup 130 (medium), 258 (firm) 31
Pink salmon, canned, with bone, 3 oz 181 27
Sardines, Atlantic, in oil, drained, 3 oz 325 27
Rainbow trout, farmed, cooked, 3 oz 173 27
Ocean perch, Atlantic, cooked, 3 oz 116 27
Most canned beans, 1 cup 69-161 17
Turnip greens, boiled, 1 cup 198 52
Chinese cabbage (bok choy), boiled, 1 cup 158 54
Spinach, boiled, 1 cup 244 5
Kale, boiled, 1 cup 94 59
Mustard greens, boiled, 1 cup 82 58
Broccoli, boiled, 1 cup 178 53
Brussels sprouts, boiled, 1 cup 56 64
Cauliflower, boiled, 1 cup 34 69
Navel orange, 1 medium 56 N/A
Orange juice, calcium fortified, 1 cup 300 25
Almonds, dry roasted, 1 cup 80 21

Thus, many green leafy vegetables, beans, calcium-fortified soymilk, and calcium-fortified 100-percent juices are equally good (and some are likely superior) calcium sources with advantages that dairy products lack. These alternate foods are excellent sources of phytochemicals and antioxidants, while containing little fat, no cholesterol, and no animal proteins that in excess can actually cause the loss of calcium from bones.

Can Too Much Calcium Be Bad?
In general, calcium absorption decreases as your intake goes up, thereby providing a protective mechanism to lessen the chances of absorbing too much. An intake of about four grams (4,000 mg) per day, however, can lead to calcium toxicity, with high blood calcium levels, severe kidney damage, and calcium deposition (milk-alkali syndrome); this condition occurs most often as a result of antacid abuse (excessive calcium carbonate intake). Supplementing with up to 1,500 mg of calcium per day appears to be safe, but use caution if you have a history of kidney stones because excess calcium can increase its excretion in urine and increases the risk of kidney stone formation. In addition, taking in too much calcium without adequate fluid intake can lead to constipation.

Moderating Your Diet in Other Important Ways
Calcium aside, bone mineral loss can be affected by your intake of other food and beverages. For instance, phosphorus-filled sodas (dark colas) are unhealthy for your bones for two reasons:
  1. they contain high amounts of phosphoric acid, which can cause an imbalance between blood levels of calcium and phosphorus, resulting in calcium loss from bones;
  2. caffeine added in most sodas can additionally mobilize bone calcium.

Ideally, your dietary intake of calcium and phosphate should be balanced equally (1:1), but many people consume up to 15 times more phosphate as it is widely distributed in foods and beverages.

High phosphorus intake may also accelerate the ability of elevated blood glucose levels to damage your body... Thus, there are many good reasons for drinking very limited amounts of phosphate-containing sodas.

The real issue is that a calcium-phosphate imbalance triggers the release of parathyroid, a hormone that causes your bones to release more calcium into your bloodstream, causing loss of this mineral when excess phosphates are consumed over a lifetime. High phosphorus intake may also accelerate the ability of elevated blood glucose levels to damage your body through the formation of advanced glycation endproducts (AGEs) that cause premature aging. Thus, there are many good reasons for drinking very limited amounts of phosphate-containing sodas.

Even higher intakes of protein may increase your bone mineral loss. The effect of excess protein intake on bone health remains unclear, but some studies show that diets that are high especially in animal protein do cause increased losses of calcium in the urine and may even increase fracture risk. These effects may be especially important if your calcium intake is marginal or low. Other studies, however, suggest that a higher protein intake is needed to promote calcium absorption, reduce the risk of fracture, and increase bone density. Until further evidence is available, it would be best for you to meet recommended calcium intakes and to consume adequate (at least 1.2 grams of protein per kilogram of body weight daily to maintain muscle mass), but not excessive, amounts of protein from non-plant sources.

Finally, a final dietary factor in bone health is total sodium intake. Sodium increases calcium losses, with an estimated five to ten mg of calcium lost with each gram of salt eaten. Thus, it is likely that reducing your sodium intake can positively impact your bone mineral content. In general, diets like Atkins that are high in protein and often sodium actually contribute to osteoporosis and are best avoided long-term for this reason, if no other.

Taking in Enough Vitamin D for Healthy Bones
[I]t's vitally important to get enough vitamin D, which helps the body absorb calcium, particularly for men over 65 and women over 50. As you get older, your skin manufactures less vitamin D in response to UV rays, so obtaining 5 to 15 minutes of sunlight exposure each day may not be adequate even though it was when you were younger. As this vitamin is fat soluble, you can also find it in fish liver oils such as cod liver oil, liver, and egg yolks. In addition, margarine, milk, and cereals are often fortified with it.

Since it's still unlikely that sunlight and food alone will provide sufficient amounts as you get older, you will likely need to supplement with vitamin D. For adults under 50, the usual recommended daily intake is 200 IU, which doubles to 400 IU once you reach 50. The potential youthful effects of having enough of this vitamin are usually underestimated, so we (and others) recommend 800 IU as an optimal daily dose for anyone 50 years of age and older.

Read more in The Science of Staying Young, 10 Simple Steps to Feeling Younger than You Are in 6 Months or Less © 2008 by John E. Morley and Sheri R. Colberg. Reprinted by permission of the authors.