Osteoporosis is a debilitating bone disease characterized by low bone mass and deterioration of bone tissue, leading to greater bone fragility and an increase in fracture risk.1 Osteopenia is a decrease in bone mineral density that often leads to osteoporosis.2 Osteoporosis is considered a silent disease because it can develop slowly over the course of many years and may go undetected until one suffers a fracture or vertebra collapse.3 In the United States, an estimated 10 million people have osteoporosis, and almost 34 million more are estimated to have low bone mass, placing them at increased risk for osteoporosis.4 Low bone mass, skeletal abnormalities and acute trauma all increase the risk for osteoporotic fractures.5 Environment (including nutrition) and genetics play important roles in the attainment of peak bone mineral density and prevention of bone loss in the adult years.6,7
Ensuring sufficient calcium intake and engaging in weight-bearing resistance exercise are two common recommendations for preventing osteoporosis and osteopenia. However, other dietary components may play a role in the treatment or prevention of bone loss, and also reduce the risk for developing fractures.
Nutrition and supplementation
Calcium, magnesium and phosphorus are structural components of bone. Attainment of peak bone mass is partially dependent upon adequate dietary intake and absorption of these nutrients. Other nutrients that affect bone mineralization include zinc, boron, copper, fluoride, manganese, silicon, and vitamins D and K.8 A number of studies have examined the intake of various vitamins or minerals and their effects on bone mineral density. However, fewer studies have examined whether supplements can actually decrease the risk of osteoporotic fractures.
Calcium provides bone with mechanical strength and serves as a reservoir that can be tapped if calcium loss exceeds calcium intake. Despite calcium's importance to bone health, however, much controversy remains over the mineral's role in preventing and treating osteoporosis, even though the U.S. Food and Drug Administration permits food and beverages rich in calcium to carry a bone-health claim.9
In a meta-analysis, researchers reviewed 15 randomized trials that examined the effect of calcium supplements or dietary calcium intake on BMD as well as on a number of fractures, in a total of 1,806 postmenopausal women. Calcium was more effective than placebo in reducing bone loss after two or more years of treatment, and there was a trend toward a reduction in vertebral fractures, but no clear relation between calcium intake and nonvertebral fractures.9
Calcium citrate and calcium carbonate are the two most commonly used forms of supplemental calcium. Calcium carbonate contains about 40 percent elemental calcium whereas calcium citrate has about 21 percent elemental calcium.10 Calcium absorption decreases as the amount of calcium consumed at one time increases. Therefore, it is best to take two or three daily doses of less than 500 mg per dose.10 Calcium carbonate should be taken with a meal so it can be broken down in an acidic environment. Calcium citrate can be absorbed if taken on an empty stomach or with food. Age, vitamin D levels and pregnancy also affect vitamin absorption.10
Another recent meta-analysis looked at all randomized trials examining calcium or calcium in combination with vitamin D and its relationship to osteoporotic bone loss, as well as fracture prevention in people 50 years or older.11 The researchers found that treatment with either calcium alone or calcium plus vitamin D was associated with a decreased risk of both bone loss and fracture. This particular analysis involved a total of 29 trials in more than 63,000 people (92 percent were women, with a mean age of 67.8 years) that each lasted between three and five years. Of the 17 trials that dealt with fractures, treatment with calcium or calcium and vitamin D was associated with a 12 percent risk reduction in fractures, which was accompanied by a reduction in bone loss in the hip and spine. Twenty-three of the 29 trials looked at BMD as an outcome of treatment, and found that supplementation with calcium or calcium and vitamin D was associated with a reduced rate of bone loss (0.54 percent) at the hip and spine (1.19 percent).
Though not statistically significant, individuals with low serum vitamin D concentration showed a greater reduction in risk compared with those with normal serum vitamin D levels. The treatment effect was also greater in people who were institutionalized, had a low body weight, low calcium intake (defined as less than 700 mg a day) or were at higher baseline risk for fracture. Risk reduction was greater in those older than 70, compared with those 50 to 70 years of age.
This meta-analysis also found that fracture risk reduction was significantly greater (24 percent) in trials with a compliance rate of 80 percent or more. In addition, the treatment effect was better in trials that used a calcium dose of 1,200 mg or more and a vitamin D dose of 800 IU or greater.
The authors of this study suggested that people older than 50 should supplement with a minimum calcium dose of 1,200 mg and 800 IU of vitamin D daily to help prevent osteoporotic fracture and bone loss.11
The USDA's current adequate intake estimate of calcium for adults age 19 to 50 is 1,000 mg per day and 1,200 mg per day for those 51 and older.8
Vitamin D promotes bone formation and mineralization. It also plays an essential role in the absorption of calcium and phosphorus from food. Vitamin D can be obtained naturally in a few foods, such as catfish and salmon; it is also available in many fortified foods and is synthesized in the skin upon exposure to ultraviolet rays from the sun.12 Despite this, many people are deficient in vitamin D, possibly due to avoidance of sunlight, prudent use of sunscreen and low calcium intake from food.13,14
Clearly, vitamin D deficiency impairs bone mineralization. But does vitamin D supplementation decrease fracture risk? In the aforementioned meta-analysis, the authors found that vitamin D did not confer any additional reduction in fracture risk or bone loss compared with calcium alone.11 However, significant differences were observed with different doses of vitamin D, and the authors noted that one limitation to the meta-analysis was the lack of studies using vitamin D doses higher than 800 IU.11
In an effort to expand upon this meta-analysis of vitamin D supplementation and fracture risk, another group of authors selected randomized controlled trials examining risk of hip fracture and oral vitamin D supplementation with or without calcium, compared with placebo or no treatment.15 Nine trials involving more than 53,000 subjects (average age of 62 or older) met the criteria for this analysis. The pooled relative risk of fracture with vitamin D supplementation alone was 1.15 percent. For the six studies that used calcium and vitamin D, the pooled relative risk of hip fracture was 0.82 percent. These data suggest that combining vitamin D with calcium reduces the risk of hip fracture by 18 percent, compared with no treatment.15
In another meta-analysis of randomized controlled trials, a group of researchers set out to estimate the effectiveness of vitamin D supplementation for preventing hip and nonvertebral fractures in people older than 60.16 Five studies examining hip fracture and seven studies examining nonvertebral fracture, each with more than 9,000 participants, were included in the analysis. All were double-blind, randomized, controlled trials that looked at the effects of vitamin D supplementation (cholecalciferol and ergocalciferol, or vitamins D3 and D2, respectively; vitamin D3 is the form of vitamin D produced in the skin upon exposure to sunlight, while D2 is created from viosterol in the body) with or without calcium in individuals 60 or older. The researchers found that 700 to 800 IU per day of vitamin D reduced the relative risk of hip fracture by 26 percent and nonvertebral fractures by 23 percent versus calcium or placebo. No significant benefit was observed in trials that used a dosage of 400 IU a day of vitamin D.16
In a meta-analysis of nine studies investigating the effects of vitamin D3 supplementation on risk of falls and fractures in primarily postmenopausal women, the researchers concluded there was a trend toward a reduction in risk of falls among patients treated with vitamin D3.17 The relative risk for vitamin D3 preventing nonvertebral fractures was 0.96 and the pooled RR for vitamin D3 preventing vertebral fractures was 1.22. In a subgroup of postmenopausal women, the pooled RR for vitamin D3 preventing falls was 0.92 and for preventing nonvertebral fractures 0.81. This analysis varied from the first one discussed, because just three studies included only postmenopausal women, the dose of vitamin D3 ranged from 400 to 800 IU per day, and all doses were pooled for the results. Will doses of vitamin D over 800 IU per day significantly affect the risk of fall and fracture? The answer to this question has yet to be determined by the research.
The current recommended intake for vitamin D is 5 to 15 ?g or 200 to 600 IU for people 19 or older.8 However, there remains much controversy over this, as some scientists recommend higher levelsâfor example, 1,000 IU per day for those not obtaining adequate sunlight.18 In addition, other vitamin D experts argue that the tolerable upper intake level of 50 ?g or 2,000 IU for vitamin D is not based on current evidence and that no toxic effects have been observed in clinical trials using doses of 250 ?g or higher (10,000 IU of vitamin D3).19
Vitamin K includes K1 (phylloquinone or phytonadione) and K2 (menatetrenone, menaquinone). K1 is the major dietary form of vitamin K, though K2 is found in some foods as well. K2 is also produced by bacteria in the intestines, and in synthetic form is used to treat osteoporosis. Studies indicate that vitamin K2 may stimulate bone formation and suppress resorption,20 reduce the incidence of vertebral fractures in those with age-related osteoporosis, and modestly improve BMD.20,21
A meta-analysis of studies that looked at the effects of oral vitamin K supplementation (phytonadione and menatetrenone) on bone loss and fracture risk included 13 trials with data on bone loss and seven reporting data on fractures. All but one study showed that both phytonadione and menatetrenone helped reduce bone loss. By pooling the results from the seven clinical trials examining vitamin K and fracture incidence, the authors found that menaquinone reduced all types of fractures (including vertebral fractures, hip fractures and other nonvertebral fractures) to a greater extent than phytonadione.22
The recommended U.S. dietary reference intake to achieve adequate levels of vitamin K for a 25-year-old male is 120 ?g per day. No tolerable upper intake level has been set. The human body stores vitamin K, so it is not necessary to take it daily. Vitamin K deficiency may occur due to disturbed intestinal uptake (as would happen with a bile duct obstruction), because of therapeutic or accidental intake of vitamin K antagonists or, very rarely, through inadequate nutritional intake.
Results of studies examining soy and bone health run the gamut from positive to negative. Some indicate that soy or components of soy, such as genistein, may improve BMD, 23,24 while others demonstrate no effect.25 In general, inconsistencies among studies make it difficult to draw conclusions.
In a review of 31 studies investigating various health outcomes associated with soy intake from supplements, refined soy products and other soy products, the Agency for Healthcare Quality and Research looked at the effects of soy on various markers of bone health, including BMD, bone formation and bone resorption.26 The group reported that it was difficult to draw a conclusion about the effects of soy on various aspects of bone health because there are few long-term randomized trials, and a wide variety of soy interventions were used in existing studies. Neither short-term nor longer-term studies demonstrated any consistent effect of soy consumption on BMD or markers of bone formation. (Long-term studies, of which there were five in the analysis, were defined as lasting a minimum of one year.) Some studies did show reductions in markers of bone resorption,27,28 but no consistent dose was used for soy isoflavones or soy protein.26
Few trials have looked at soy consumption and fracture risk. One epidemiological study investigated the effects of soy consumption over a 4.5-year period in 24,403 postmenopausal women who had no history of fractures. The researchers found that increased soy intake was associated with an increase in fracture risk, which was more pronounced in women in the early stages of menopause. Yet it is unclear if these fractures were related to osteoporosis, as the study did not examine BMD levels.29
About half of the body's magnesium stores are found in bone, and adequate magnesium stores are essential for good bone health.30 Magnesium deficiency has been related to osteoporosis, and some epidemiological studies have revealed a direct relationship between magnesium intake and bone mineral density in postmenopausal women32,33,34,35 and elderly individuals.36 Some older studies demonstrated no association between the two.37,38 Despite the relationship between magnesium and bone health, very few clinical trials or epidemiological studies have examined magnesium intake and risk of fracture. One study in particular, the Women's Health Initiative, showed a higher risk of wrist fracture with higher magnesium intakes.39
The relationship between magnesium intake, BMD and fracture risk remains unclear. Even less transparent is the relationship between bone health and low magnesium intake over time (as opposed to true deficiency). Though true deficiency is rare in the United States, many individuals do not meet the recommended intake for magnesium,31 and it has been postulated that American's typical daily intake may not be sufficient to prevent some chronic diseases, including osteoporosis.40
Tea has anti-inflammatory properties, and consumption of tea has been associated with everything from protection against cardiovascular disease to weight control and better oral health.41
Though researchers have theorized that green tea may be a potential treatment for osteoporosis, too few randomized, controlled trials have examined its effects on the prevention and treatment of osteoporosis, and the few studies that are available offer conflicting evidence.42
In a prospective study examining risk factors for hip fracture in men age 50 or older, 730 men were enrolled in 14 centers in five different countries. Of several variables examined, tea consumption was actually associated with an increased risk of hip fracture.43 In a similar study examining hip fractures in women, the results were very different. Low tea consumption was correlated with an increase in fracture risk.44 Few studies and lack of correlation among conclusions indicate it is too early to make a determination about the effects of tea and BMD or risk for fracture.
Currently, calcium, vitamin K2 and vitamin D (in doses of 700 to 800 IU a day) show the most promise in preventing bone loss and decreasing risk of fracture. Other supplements that have been examined for their potential role in maintenance of bone mass and prevention of osteoporotic fractures include phosphorus and prebiotics. It remains unclear if soy or tea confers benefits that translate to real improvements in bone health.
Marie Spano, M.S., R.D., is vice president of the International Society of Sports Nutrition, a freelance writer, and food and supplement industry consultant.
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