Osteoporosis
What is it?
Osteoporosis, which literally means "porous bones", is the result of a long-term decline in bone mass which, in severe cases, causes the bones to break under the weight of the body. Particularly badly affected bones include the spinal vertebrae, the thigh bone and the radius (shorter arm bone). Over 25 million Americans may be affected by osteoporosis and 80 per cent of those are women. Although the problem also occurs in men, postmenopausal women are particularly susceptible, with around 35 per cent of women suffering from osteoporosis after menopause.
Symptoms of osteoporosis
The symptoms of osteoporosis are often absent until fractures occur, although in some cases there may be a loss of height, a hunched back or back pain. Osteoporotic fractures affect 50 per cent of women and 30 per cent of men over 50. These fractures are particularly serious as demineralized bones shatter when they break and usually take longer to heal. Radiological examination can be used to measure bone mineral density and assess the risk of fracture.
Causes of osteoporosis
Around 35 per cent of women suffer from osteoporosis after menopause and, although it is less common, the problem occurs in a similar way in men. Osteoporosis is more common in Caucasians and Asians because they are often smaller boned.
Most of the bone loss seen in osteoporosis in women occurs in the first five to six years after menopause due to a decline in circulating female hormones and an age-related reduction in vitamin D production. Genetic factors seem to play a part in osteoporosis but behavioral and hormonal factors may be more important. Sufficient body fat and muscle are necessary to keep hormone levels high enough to maintain bone mineral content. Athletes and premenopausal women whose menstrual periods have stopped may also be at increased risk of osteoporosis due to alterations in their hormone levels.
Adequate intakes of calcium, vitamin D, magnesium and boron are also necessary. Diets high in dairy products, protein, sugar, alcohol, salt, caffeine-containing drinks and very high in fiber also seem to increase the risk of the disorder, most likely due to effects on mineral absorption and metabolism. People on weight-reducing diets are also at risk as they avoid foods high in bone-building nutrients.
Inactivity leads to an increased risk of osteoporosis, as does gastric surgery and certain types of medications such as corticosteroids.
Treatment of osteoporosis
The conventional treatment for osteoporosis is estrogen therapy but this is not suitable for some women due to the increased risk of breast cancer. Some women are treated with calcitonin, a hormone that inhibits removal and promotes formation of bone. It is available in injection forms and as a nasal spray. Intake of calcium and vitamin D must also be adequate. Newer osteoporosis drugs include alendronate, which inhibits bone breakdown; and raloxifene, a selective estrogen receptor modifier.
Preventing osteoporosis
Exercise
Regular exercise plays a vital part in preventing loss of bone mass. Weight-bearing exercises such as walking, jogging and yoga contribute to increases in bone density and prevention of bone loss. Exercise also helps build muscle mass which can help protect bones from injury. It also improves strength and flexibility, decreasing susceptibility to falls.
Diet
A healthy diet can reduce the incidence of osteoporosis by ensuring the development of a favorable peak bone mass during the first 30 to 40 years of life. Adequate nutrient intake early in life is vital for bones to reach their maximum density so that they are strong enough to support the body even when they lose mass later in life. However, it is never too late to slow the bone loss seen in osteoporosis, and early postmenopausal years are an important time to ensure optimal intake of nutrients including calcium, magnesium, boron and vitamin D.
Recent research suggests that including soybeans in the diets of postmenopausal women may decrease the risk of osteoporosis. Soybeans contain compounds called phytoestrogens which act in a similar way to estrogen and have beneficial effects on bone mineral density.
Caffeine-containing drinks can increase the loss of calcium in the urine. Diet soda drinks which contain phosphoric acid can alter the calcium phosphorus balance and contribute to calcium loss from the bones. Consuming large amounts of these drinks can increase the risk of osteoporosis. Nicotine and alcohol also adversely affect bone mineral density. High salt intakes seem to increase calcium excretion, lowering bone mineral density and increasing the risk of osteoporosis. In a study published in 1995, Australian researchers investigated the influence of urinary sodium excretion on bone density in a 2 year study of 124 postmenopausal women. The results showed that increased sodium excretion was linked to decreases in bone density.1
While dairy products are good sources of calcium, there is concern that their protein content can actually increase the loss of calcium from bone. Researchers involved in the Nurses Health Study analyzed the diets of over
77 000 participants in the study and looked at the rates of bone fractures. Results showed that women who drank two or more glasses of milk per day had around a 45 per cent increased risk of hip fracture and a 5 per cent increased risk of forearm fracture compared to women who drank one glass or less per week. There was also no drop in risk with intake of calcium from other dairy foods.2 A varied diet which includes nondairy sources of calcium is likely to be more beneficial in protecting against osteoporosis.
Vitamins, minerals and osteoporosis
B vitamins
B vitamin deficiencies may contribute to osteoporosis, particularly those of folate, vitamin B12 and vitamin B6. This may be partly due to the effects of increased homocysteine levels on bone metabolism.
Vitamin D
Vitamin D regulates the absorption and use of calcium and phosphorus, which are vital for normal growth and development of bones. Vitamin D is necessary for calcium absorption and increases the deposition of calcium into bones. In cases of vitamin D deficiency, the body increases production of parathyroid hormone which removes calcium from the bones and leads to bone thinning.
Research suggests that there may be a genetic link between vitamin D receptor types and osteoporosis. It is also possible that patients with osteoporosis have impaired conversion of vitamin D to its most active form. The ability to produce vitamin D in the skin may decline with age and bone loss may increase in the winter months when people have less exposure to sunshine. People with a certain type of vitamin D receptor may be more susceptible to osteoporosis, and research suggests that women with different types of vitamin D receptors respond differently to vitamin D supplements.3
A study done in 1997 at Tufts University in Boston showed reduced rates of bone loss and fractures in men and women over 65 who took calcium and vitamin D supplements. Researchers assessed the effects of calcium (500 mg per day) and vitamin D (700 IU per day) on 176 men and 213 women aged 65 years or older. After a three-year period, those taking the supplements had higher bone density at all body sites measured. The fracture rate was also reduced by 50 per cent in those taking the supplements.4
Vitamin D supplements may also be useful in preventing bone loss in patients taking corticosteroid drugs. In a study published in 1996, researchers at the University of Virginia found that calcium and vitamin D supplements helped prevent the loss of bone mineral density in those taking the drugs for arthritis, asthma and other chronic diseases.5 Vitamin D supplements may also be useful in reducing the risk of osteoporosis due to long-term use of anticonvulsant drugs.
However, other studies have not shown any reduction in fracture rates in those taking vitamin D supplements. A 1996 study which was carried out in Amsterdam looked at the effects of either vitamin D or a placebo on 2500 healthy men and women over the age of 70 who were living independently. The participants received a placebo or a daily dose of 400 IU of vitamin D for a three-and-a-half year period. Dietary calcium intake was the same in both groups. Forty-eight fractures were observed in the placebo group and 58 in the vitamin D group.6
Vitamin K
Low levels of vitamin K have been seen in sufferers of osteoporosis. In a Japanese study published in 1997, researchers investigated the relationship between bone mineral density, vitamin K levels and other biological parameters of bone metabolism in 71 postmenopausal women and 24 women with menopausal symptoms receiving hormone replacement therapy. The results showed that women with reduced bone mineral density had lower levels of vitamin K1 and K2 than those with normal bone mineral density.7 Low levels have also been seen in osteoporotic men.8
Boron
Boron acts with calcium, magnesium and phosphorus in the metabolism of bone. Deficiency seems to affect calcium and magnesium metabolism and affects the composition, structure and strength of bone, leading to changes similar to those seen in osteoporosis.9 Combined boron and magnesium deficiency seems to worsen osteoporosis, suppress bone building and cause decreased magnesium concentrations in bone.10 Supplements of around 3 mg per day have been shown to enhance the effects of estrogen in postmenopausal women. This is likely to contribute to its beneficial effects on bone health.11 Studies done in 1994 in athletic college women suggest that boron supplements decrease blood phosphorus concentration and increase magnesium concentration. Both of these changes are beneficial to bone building.12
Calcium
Osteoporosis is not merely a loss of calcium from bone, although calcium deficiency does contribute to osteoporosis. The National Osteoporosis Foundation estimates that the average adult in the US gets only 500 to 700 mg per day. The US government has recently raised its recommendation for daily calcium intake. For men and women aged from 19 to 50, the RDA is now 1000 mg, and for those over 50 it is 1200 mg.
The new RDA for adolescents is 1300 mg and adequate calcium intake during this time of life plays a vital part in allowing bones to reach their maximum density so that they are strong enough to support the body even when they lose density later in life. Studies suggest that calcium intake in adolescence is often below the recommended levels. Researchers involved in a 1994 USDA study measured calcium intake in 51 girls aged 5 to16 years old. They found calcium intake to be below the recommended dietary allowance for 21 out of 25 girls aged 11 or over. These studies suggest that the current calcium intake of American girls during puberty is not enough to enable bones to develop maximum strength, and that increased intakes may be necessary.13 A 1993 study published in the Journal of the American Medical Association suggests that calcium supplements may be beneficial in adolescent girls. Researchers gave daily calcium doses of 500 mg or placebo to 94 girls and then measured bone mineral density and bone mineral content at the lumbar spine. The results showed that increasing calcium intake led to significant gains in bone mass.14
However, it is never too late to slow the bone loss seen in osteoporosis, and early postmenopausal years are also an important time to ensure optimal intake. A 1997 study done at King's College Hospital in London suggests that high calcium intakes are linked to bone mineral density in elderly women. Researchers assessed calcium intake in 124 women aged from 52 to 62 and also measured bone mineral density at the spine, hip and the os calcis bone in the foot. Results showed that women with high calcium intakes had higher bone mineral density.15 Results from the Rotterdam Study, which involved 1856 men and 2452 women aged 55 years and over, show that high calcium intakes also protect against bone loss in men.16
Taking calcium supplements later in life can slow the bone loss associated with osteoporosis, and treatment which combines calcium and estrogen is likely to be better at building bone than treatment with estrogen alone. In a 1998 study, researchers analyzed the results of 31 studies and found that the postmenopausal women who took estrogen alone had an average increase in spinal bone mass of 1.3 per cent per year, while those who took estrogen and calcium supplements had an average increase of 3.3 per cent. Increases in bone mass in the forearm and upper thigh were also greater in women taking supplements. The added benefit from the calcium was seen when the women increased their intake from an average of 563 mg per day to 1200 mg per day.17
It is recommended that postmenopausal women who are not on estrogen therapy consume 1500 mg calcium per day. Multivitamin supplements often do not provide enough calcium and separate supplements may be necessary. Supplements should be taken in divided doses throughout the day, with a maximum of 500 mg being taken at any one time.
Fluoride
Bones seem to be more stable and resistant to degeneration when the diet is adequate in fluoride. Sodium fluoride supplements have been used to treat osteoporosis.3 Researchers involved in a 1998 study published in the Annals of Internal Medicine compared the vertebral fracture rates in 200 women over a four-year period. One group was given 20 mg of fluoride and 1000 mg of calcium daily, and the other group received only calcium. The rate of new fractures in the fluoride group was 2.4 per cent compared to 10 per cent in the calcium only group.18 Sustained release of fluoride in doses of 23 mg per day appears to be more beneficial than forms which are quickly absorbed from the gut.19 However, a 1996 study done in Argentina suggests that the increases in bone mineral density are not maintained after sodium fluoride therapy is stopped.20
The treatment of osteoporosis with fluoride supplements is controversial as there is the possibility that fluoride bone is not always stronger than normal bone. There may be an increase in the number of hairline fractures in the hips, knees, feet and ankles. In 1983/1984, a study of bone mass and fractures was begun in 827 women aged 20-80 years in three rural Iowa communities selected for the fluoride and calcium content of their community water supplies. Residence in the higher-fluoride community was associated with a significantly lower radial bone mass in premenopausal and postmenopausal women, an increased rate of radial bone mass loss in premenopausal women, and significantly more fractures among postmenopausal women.21 Fluoride therapy may increase the requirement for calcium as more is needed for bone formation.
Magnesium
Magnesium and calcium interact in many body functions including that of bone formation. Women with osteoporosis may have lower magnesium levels than women without the disorder. In a 1995 study, results showed that women whose dietary intakes were less than 187 mg per day had a lower bone mineral density than women whose average intakes were more than 187 mg.22
Magnesium is essential for the normal function of the parathyroid glands, metabolism of vitamin D, and adequate sensitivity of bone to parathyroid hormone and vitamin D. Magnesium deficiency may impair vitamin D metabolism which adversely affects bone building.23 Magnesium deficiency is also known to cause resistance to parathyroid hormone action which affects calcium balance and may cause abnormal bone formation.24 However, magnesium excess inhibits parathyroid hormone secretion which means that bone metabolism is impaired under positive as well as under negative magnesium balance.25 Maintaining normal calcium-to-magnesium balance is very important in the prevention of osteoporosis.
Supplements may help to increase bone mineral density in postmenopausal women, thus reducing the risk of osteoporosis. In a 1990 study, US researchers investigated the effect of a dietary program emphasizing magnesium instead of calcium for the management of postmenopausal osteoporosis. Nineteen women on hormone replacement therapy (HRT) received 500 mg magnesium and 600 mg calcium, and seven other women on HRT did not receive supplements. The results showed that in one year, those women given the supplements had greater increases in bone mineral density than those who were not. Fifteen of the 19 women had had bone mineral density below the spine fracture threshold before treatment; within one year, only seven of them still had values below that threshold.26
In a 1993 study, Israeli researchers assessed the effects of supplemental magnesium in 31 postmenopausal women who received six 125 mg tablets daily for six months and two tablets for another 18 months in a two-year trial. Twenty-three symptom-free postmenopausal women were assessed as controls. The results showed that 22 patients responded with a 1 to 8 per cent rise of bone density. The mean bone density of all treated patients increased significantly after one year and remained unchanged after two years. In control patients, the mean bone density decreased significantly.27
Zinc
Zinc accompanies calcium in the mineralization of bone, and is lost when calcium is lost from bone. Recent research in monkeys suggests that diets low in zinc during adolescence may increase the risk of osteoporosis later in life, as bones may not develop properly.
In a 1996 study, researchers studied zinc deficiency in two groups of ten monkeys. Both groups were given nutritionally balanced diets but one group received 50 mg of zinc per gram of food while the other group only received 2 mg of zinc per gram of food. Eight of the monkeys were then studied throughout their lives to ages equivalent to that of ages 10 to 16 in human girls. The researchers found that the monkeys on low zinc diets had slower skeletal growth, maturation and less bone mass than the other monkeys, with substantial differences noticed in the lumbar spine. The differences were only apparent during rapid growth phases in the monkeys, especially during pregnancy.28
Other minerals
Chromium may help to boost the bone-building effects of insulin and may have a role in the maintenance of bone density and prevention of osteoporosis.29 Copper is necessary for bone formation, and inadequate intake can cause the loss of calcium from bones, reduced bone formation and deformities. Manganese deficiency may also increase loss of calcium from the bone. Silicon may have a role in the prevention and treatment of osteoporosis, and supplements are used to increase bone mineral density.
Herbal medicine and osteoporosis
Herbs used to treat osteoporosis include horsetail (Equisetum arvense), oat straw (Avena sativa), alfalfa (Medicago sativa) and hawthorn (Crataegus oxyacantha). Herbs commonly used to alleviate the side effects of menopause include black cohosh (Cimicifuga racemosa) and dong quai (Angelica sinensis).