Dietary Calcium and Prevention of Osteoporosis
Osteoporosis, characterized by the loss of bone density and strength, is the major underlying cause of bone fractures in postmenopausal women and the elderly. We now know that by maintaining a calcium-rich diet from childhood onward, we can dramatically improve our odds of escaping this disease.
Osteoporosis-related fractures can occur in any bone, with the most common being the spinal column, the hip and the wrist. Rapid loss of bone mass starts occurring in a woman’s spinal column following menopause. Once it has progressed far enough, a simple action, such as bending forward, can produce enough pressure to cause a spinal compression fracture, resulting in chronic pain and loss of height. Wrist fractures also occur frequently among women with osteoporosis. Hip fractures in older adults are among the most serious health problems. Broken hips are associated with more deaths, disability and higher medical costs than all other osteoporosis-related fractures put together. Up to 20% of the elderly die within a year of breaking their hips due to osteoporosis. Fewer than half of the survivors return to the full level of activity they previously enjoyed.
Risk Factors for Osteoporosis
- Age. Whilst denser bones delay the onset of osteoporosis, normal aging inevitably includes some gradual loss of bone mass.
- Heredity. A history of broken bones or stooped posture among older family members, particularly women, can be a warning that you too are at risk.
- Ethnic background. Asian and Caucasian women and men are at greater risk than Africans, whose bone mass is generally about 10% greater.
- Gender. Osteoporosis is known to be far more common in women than in men because women’s bones are usually less dense to begin with but also because the lower estrogen levels that accompany menopause cause women to lose bone mass more rapidly.
- Early menopause (before the age of 45). The sooner estrogen levels decrease, the greater the chances of developing osteoporosis.
- Lack of weight-bearing exercise. The significant loss of bone mass in astronauts demonstrates the importance of weight-bearing exercise, especially walking, in maintaining strong bones.
- Body weight. Thin, small-boned women face an increased risk of developing osteoporosis. Studies show that an adult weight of less than 125 pounds/57 kilograms and a lack of menstrual periods for more than a year increase the risk of developing osteoporosis.
- Other health conditions. Rheumatoid arthritis, hyperthyroidism, kidney disease and certain cancers may also lead to osteoporosis.
- Medications. Osteoporosis can occur as a side effect of prolonged use of anticonvulsants, thyroid hormones or steroid drugs.
- Alcohol and smoking. Heavy drinkers and smokers tend to have weaker bones. Alcohol disrupts bone formation while smoking decreases absorption of calcium.
Role of Calcium in our Bones
Our bones are in constant change. Certain hormonal signals trigger the breakdown of old bone, while others encourage new bone deposits which is called bone remodelling. When we are young, old bone is replaced by new bone every three months. Once we reach peak bone mass (between the ages of 25 and 35), the rate of bone dissolution surpasses the rate of new bone creation, resulting in gradually decreased bone mass and density and our bones begin to lose their strength.
Virtually all of the calcium in our body is stored in bones and teeth. Calcium not only makes our bones hard but also helps our blood to clot and enables our heart and other muscles to contract. Whenever our dietary intake of calcium is too low to meet our body’s requirements, increased amounts are drawn from the bones to maintain a constant supply in the bloodstream.
A vast body of evidence confirms the need for adequate calcium intake during early life to build denser, stronger bones as well as later in life to slow down the rate of natural bone loss. Although everyone experiences some bone loss with age, osteoporosis and resulting bone fractures are not a normal part of aging. Since there is no real cure for osteoporosis, prevention is paramount. The good news is that if we take steps to curb the rate of natural bone loss in later life, such as by consuming the adequate amounts of calcium and committing to regular exercise, we reduce our risk of developing the condition.
Recent scientific data shows that the bone mass you build early in life is probably the most important factor in determining your bones’ long-term health. The recommended dietary allowance (RDA) for kids over 4 years of age is 1,000mg whereas teenagers should get 1.300mg of calcium daily. In order to avoid depletion of bone mass and reduce the risk of osteoporosis-related fractures during midlife, a daily calcium intake of 1,000mg is recommended. Because older adults have more problems absorbing calcium than do younger people, women over 50 and men over 70 should boost their calcium intake to 1,200mg daily.
Good Dietary Sources of Calcium
We can achieve our RDA of calcium by eating a calcium-rich diet or calcium-fortified foods, taking calcium supplements and by combining these strategies. Vitamin D improves calcium absorption, while certain foods and medications reduce its availability.
Dietary sources of calcium are not hard to find. Milk and dairy products are naturally rich in this vital mineral. They also provide vitamins A and D, protein, phosphorus and magnesium, the other building blocks for bone. Other non-dairy calcium-rich foods include fish (sardines salmon, etc.), soy (soymilk, tofu, green soybeans) as well as some vegetables (kale, collard greens, broccoli, turnip, etc.), fruits (figs, oranges) and nuts (almonds).
Consuming calcium-fortified foods is also a valid way of boosting our calcium intake. These foods and beverages are suitable for those who do not like or do not tolerate dairy products and do not get enough calcium from other non-dairy sources. But they happen to be more like supplements than natural dietary sources of calcium. Though most experts strongly recommend a calcium-rich diet as the preferred source of this essential mineral, calcium-fortified foods and supplements can provide an alternative. Calcium is being added to many foods and beverages, so it is possible to get far more than the recommended dietary allowance, especially if you also take supplements. Too much calcium can increase the risk of kidney stones. Therefore, people who are at risk for kidney stones should better avoid supplements and calcium-fortified foods.
Factors that Can Influence our Calcium Levels
The body’s ability to use the calcium we consume depends not only on the total calcium intake but also on other dietary elements that can either enhance or inhibit its absorption. A good example is the absorption of calcium from some cruciferous vegetables such as kale or broccoli, which compares favorably to the absorption of calcium from milk, whereas spinach (not considered to be a part of cruciferous family) is not a good source due to poor absorption. Salt increases the loss of calcium through the urine, whilst high amounts of fiber tend to reduce its absorption. Here is the list of the most common factors that can affect our calcium status:
- Vitamin D promotes absorption of calcium from the intestines into the bloodstream.
- Salt. The high sodium content of many foods can play havoc with our calcium level. Sodium pulls large amounts of calcium into the kidneys, where it is then lost through the urinary tract.
- Protein. While it is true that protein encourages loss of calcium through the urine, most protein-rich foods, such as meat, eggs and milk, contain high levels of phosphorus, which has the opposite effect. The net effect of these foods on our calcium balance is thus of little concern, provided we eat them in moderate amounts and get enough calcium. However, in excessive amounts both protein and phosphorus can have negative effects on our calcium status.
- Phosphorus. Although phosphorus tends to suppress the urinary loss of calcium, its excess can negatively affect calcium absorption as these two minerals compete for vitamin D that is required for their metabolism.
- Estrogen replacement therapy. Since estrogen is crucial for preserving bone density in women, doctors often recommend estrogen replacement therapy or hormone replacement therapy at menopause. Hormone replacement therapy, coupled with a calcium-rich diet and moderate exercise, is a proven strategy to prevent rapid loss of bone density after menopause.
- Medications. Several drugs offer alternatives to postmenopausal women who cannot tolerate or do not wish to use estrogen replacement therapy. Alendronate (Binosto, Fosamax) inhibits bone resorption and promotes bone build-up, leading to increased bone density. Other drugs approved for use in prevention and treatment of osteoporosis include a selective estrogen-receptor modulator Raloxifene (Evista) and Risedronate sodium (Actonel, Altevia and Benet). For those women who have already been diagnosed with osteoporosis, doctors may opt to prescribe calcitonin. This naturally-occurring hormone helps to regulate calcium absorption and bone development and slows the natural breakdown of bone. Calcitonin is available in injection form or as a nasal spray under trade names Calcimar, Fortical and Miacalcin.
- Tobacco. Smoking can damage bones and additional calcium intake often cannot compensate for it. Heavy smokers usually show lower bone density than non-smokers whereas women who smoke tend to experience an earlier menopause.
- Exercise. Weight-bearing exercise is important for preventing osteoporosis. Walking, perhaps the most beneficial weight-bearing exercise, can help to maintain overall body strength and stability even in very old people. People who are at risk of developing osteoporosis should make exercise an integral part of their life.
Prevention of osteoporosis requires attention to diet and lifestyle issues throughout our entire lives. No matter what our age or the present state of our bones, it is never too late to slow the process of osteoporosis and reduce the risk of broken bones. Eating a balanced diet that includes adequate amounts of calcium and moderate levels of salt while staying physically active should help us maintain bone strength till ripe old age.
Where to Get More Information: National Osteoporosis Foundation