For many, the word "osteoporosis" conjures up images of frail, elderly women, hunched over beneath dowager's humps, with canes in hand. But the roots of this disease actually begin to grow many decades earlier, in childhood and early adulthood. Below you will learn about who is most at risk for this disease, and what can be done to maintain good bone health early, to prevent osteoporosis later.
Bone as Living Tissue
To understand the origins of osteoporosis, you need to know a bit about bone physiology. Bone is vital, living tissue that provides structural support for our bodies as well as a reservoir of minerals for maintaining normal body chemistry. The majority of bone tissue (65%) consists of hard minerals: calcium, phosphate, magnesium and others. The remaining 35% of our bone contains a soft protein called collagen. This combination of hard and soft materials lends bone its strength and flexibility.
Scattered throughout our bones are two important types of bone cells called osteoclasts and osteoblasts. These cells perform the critical function of bone remodeling, in which old or damaged bone is taken away, or resorbed, and new, healthy bone is laid down in its place. The job of osteoclasts is to eat away the old bone, then osteoblasts come in to lay down the new bone. Throughout childhood and into our twenties, bone formation exceeds bone resorption, so that we are truly building stronger and healthier bones. After about age thirty, however, for reasons that are still unclear, this process starts to reverse, and bone resorption slightly outstrips bone formation. By age thirty, most of us have achieved our peak bone mass, and then we start to lose bone very slowly.
Understanding Peak Bone Mass
Every person has a biologically determined peak bone mass. By this I mean that gender, race, and other hereditary factors predetermine the maximum amount of bone that each of us can develop by the time we reach our thirties. Women tend to have lower peak bone masses than men. African Americans tend to have higher peak bone masses than Caucasians. About 80% of this peak bone mass is hereditary while the other 20% is affected by lifestyle and other factors.
A woman may be genetically "programmed" to have a normal peak bone mass at maturity. If she has an unhealthy lifestyle, however (smoking, poor diet, and so on), she may only achieve 80% of her potential peak bone mass, and end up with bones that are less dense than she might have had otherwise. In contrast, another woman may be destined to have a rather thin skeleton due to hereditary factors so that even with an ideal lifestyle, her peak bone mass may measure significantly below that of her peer group.
I often see women in their early forties who bring in the results of a "baseline" bone density measurement test and are shocked to find that they have osteopenia (mild low bone mass) or even osteoporosis (more severe low bone mass). They ask me why they are losing bone so rapidly. In the vast majority of cases, these women are not rapidly losing bone and in fact, have perfectly healthy, normal bone tissue, just less of it. They wonder why, then, if their bones are healthy, they have less bone than the "average" woman's. I explain to them that, ten to twenty years ago, they probably achieved a lower peak bone mass than the "average" woman, probably due to genetic factors. Some women just have smaller and thinner bones than other women.
To understand peak bone mass in another way, think of your skeleton as a retirement bank account. From birth until age 30 or so, you continually make deposits into your account. When you retire at age 30, the deposits stop and you have to start making withdrawals for the rest of your life. Thus, the size of your bank account at age-30-retirement is analogous to your peak bone mass. This is the bone you will have to work with for the rest of your life.
Maximizing Peak Bone Mass
Obviously, we would all like to have the strongest skeletons possible (or the biggest bank accounts!) by the time we reach our thirties. To some extent, this is predetermined by genetics, as mentioned above. Some of us inherit a good skeleton from our families and some of us don't. We can't change our families or our inheritances. What we can change are our lifestyles that account for up to 20% of peak skeletal mass. By "lifestyle" I mean diet, exercise, and habits. A final critical factor is the role of sex hormones.
Diet
Good bone health begins in childhood with the two most important building blocks of the skeleton: calcium and vitamin D. Children need the calcium from milk and other dairy products and green vegetables, such as broccoli and kale, to achieve the strongest bones possible.
To get adequate amounts of calcium, you will need at least 3-5 servings of dairy or other foods high in calcium each day. A typical serving of milk (1 cup) or yogurt (1 cup) contains about 300-400 mg of calcium. Half a cup of ice cream contains 100 mg of calcium. Green vegetables are also good sources of dietary calcium. If your dietary calcium does not add up to what you need, calcium supplements may be used.
So, for children and young adults, it is critical to encourage diets rich in dairy products and to avoid excess amounts of soda and caffeine. The table below shows how your need for calcium varies according to your age and gender. These are the recommended daily allowances for calcium, adapted from the National Academy of Sciences (1997):
Children and young adults
| 1-10 year olds |
800-1200 mg/day |
| 11-24 year olds |
1200-1500 mg/day |
Adult women
| Pregnant or nursing women |
1200-1500 mg/day |
| 25-49 year olds (premenopausal) |
1000 mg/day |
| 50-70 year olds who are on estrogen therapy |
1200 mg/day |
| 50-70 year olds who are not on estrogen therapy |
1200 mg/day |
| Women over 70 |
1200 mg/day |
Adult men
| 25-64 year olds | 1000 mg/day |
| Men 65 years and older | 1500 mg/day |
Vitamin D
The second critical building block of bone is vitamin D. We need this vitamin in order to absorb calcium from our gastrointestinal tracts and to allow the deposition of calcium and phosphorus into our skeletons. Exposure to sunlight allows our skin to make vitamin D. Most children who play outdoors during the summer months will get enough vitamin D this way.
Who is at risk of vitamin D deficiency?
Those who do not spend much time outdoors or who wear clothing and sunblock to protect their skin from the ultraviolet rays may be at risk of vitamin D deficiency. African Americans are at risk for vitamin D deficiency since their darker skin pigment may block its formation in the skin. At highest risk for vitamin D deficiency are the elderly, especially those who are homebound or in nursing homes.
Osteomalacia
Severe vitamin D deficiency leads to a condition called "osteomalacia", which can be detected on a bone biopsy. The bone tissue in those with osteomalacia shows a marked deficiency of calcium and phosphorus minerals. Patients with osteomalacia suffer from osteoporotic fractures as well as from generalized weakness, difficulty walking, and sometimes bone pain.
The daily requirement for vitamin D is 400 IU (International Units) until age 65, at which time 600-800 IU per day are recommended. Foods containing vitamin D include fortified dairy products, egg yolks, saltwater fish, and liver. To be sure you are getting an adequate amount, I suggest a daily multivitamin that contains 400 IU of vitamin D. For older adults, a calcium supplement containing an extra 400 IU of vitamin D along with a multivitamin is usually sufficient. Occasionally, we need to prescribe extremely large doses of vitamin D, such as 50,000 IU per week, in order to treat patients with osteomalacia.
Exercise
Like muscle, our bones become stronger with exercise and use. The expression "If you don't use it, you lose it" applies to the skeleton. Regular weight-bearing exercise is critical for maintaining a healthy skeleton. By "weight-bearing", I mean any exercise that requires you to support yourself against gravity, namely walking, hiking, jogging, dancing, and so on. People who are weightless (such as astronauts in outer space), those immobilized in bed, or those confined to wheelchairs are susceptible to severe bone loss and osteoporosis.
The ideal weight-bearing exercise is anything you are willing to do on a regular basis. If you can walk for 20-30 minutes several times per week, you are doing well. For the elderly person, regular walking can improve muscle tone, balance, and flexibility in addition to bone mass. Such people are much less prone to falls and fractures than their sedentary peers.
Though we think of exercise as a virtue of good health, too much exercise can be detrimental to the growing skeleton. I've seen a number of teenage girls in my practice who have developed painful stress fractures due to excessive weight-bearing exercise. These young women run marathons or compete in track and field, gymnastics, ballet, and other highly competitive sports. Often, these women do not menstruate and have very low levels of estrogen. Despite all the exercise, they never succeed in building strong skeletons and may even start having fractures at a relatively young age, even in teenage years and early twenties. Thus, exercising to the point of menstrual irregularity or loss of periods altogether is definitely not good for bone health.
Eating disorders
Unfortunately, one of the most common reasons for low peak bone mass among young women is the presence or history of eating disorders. Anorexia nervosa, a potentially life-threatening psychologic disturbance that leads to severe food restriction, can result in devastating skeletal consequences. Milder forms of eating disorders may cause a young woman to lag well behind her peers in her skeletal development. Unfortunately, even after a young person has been successfully treated for an eating disorder, the effects on the skeleton may be irreversible.
Lifestyle habits
There are already so many good reasons not to smoke that we hardly need another. But it is clear that ingredients in tobacco are toxic to the skeleton at any age. Smoking is a major risk factor for osteoporosis and fractures in adults and a major cause of failure to achieve maximum peak bone mass in the young. If you do smoke, quitting now will help restore your bone health and reduce your risk of future fractures. If you don't smoke, don't start. Excessive alcohol use is also detrimental to the skeleton and should be avoided. If you drink more than 2 to 3 ounces of alcohol daily, you are at an increased risk for bone loss, fractures, and falls.
The Role of Sex Hormones
During puberty, both males and females experience tremendous growth in the size and strength of their skeletons. To a large extent, this process depends upon normal levels of sex hormones (testosterone for boys and estrogen for girls). Any disorder that interrupts the normal production of sex hormones in the teenager or young adult will adversely affect bone development and achievement of peak bone mass. The teenage girl who suffers from anorexia nervosa or who exercises to the point of losing her periods will never develop the peak bone mass she was destined to develop. Girls or boys with pituitary disorders, chromosomal abnormalities, serious medical illnesses and other more unusual causes of hormonal disruption will suffer skeletal consequences.
Later in life, postmenopausal women are at risk for accelerated bone loss due to lack of estrogen. Men also lose bone, but at a slower rate, as testosterone levels decline with age. Hormone replacement therapy as well as other anti-resorptive therapies can help prevent bone loss and even rebuild part of what was lost.
A Strategy for Prevention of Osteoporosis Throughout the Life Cycle
Strategies for good bone health start early in life and continue until we die. We need to teach our children and grandchildren the importance of healthy diet, adequate calcium, exercise and avoidance of toxic behaviors, such as smoking and heavy drinking. For those of us in middle age and beyond, we need to continue to live by these fundamental principles, and perhaps consider medications to help us obtain the healthiest skeletons we can achieve. For our elderly population, we also need to prevent fractures by lowering the risk of falls and making the home environment a safer place to be. With these measures taken, we can look forward to brighter futures free of pain, disability, disfigurement and dependency.
©2007 Healthology, Inc.