Topic of the Month

Micronutrients for bone health

January 1, 2011

Bones make up the human skeleton and provide structure, mobility and support while protecting the various organs of the body. Although bones may seem like hard and lifeless structures, they are living tissues. During a person’s lifetime the body constantly breaks down old bone and builds up new bone. Any time old bone is broken down faster than new bone is made, net bone loss occurs.  

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Bone loss can lead to osteoporosis, a disease in which bones become weak, fragile and more likely to break. Osteoporosis can progress without pain or symptoms until a bone breaks. Fractures commonly occur in the hip, spine and wrist. About 75 million people are currently affected by osteoporosis in the EU, USA and Japan alone. The key to reducing the risk of osteoporosis and poor bone health is strengthening bones from an early age and minimizing the chance of a fracture.

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Bone loss

Bone is made mostly of collagen, a protein that is woven into a flexible framework. In addition, bone contains calcium phosphate and calcium carbonate, minerals that add strength and harden the framework. The combination of calcium and collagen gives the bone its strength and flexibility and protects it from breaking. Bone also acts like a storehouse for calcium: more than 99% of the body’s calcium is contained in the bones and teeth. The remaining 1% is in the blood.

Even though it is mostly made of protein and minerals, bone is living, growing tissue. Throughout a person’s lifetime, old bone is broken down (‘resorption’) and new bone is added to the skeleton (formation). When more bone is broken down than is added to the skeleton, bone loss occurs. Many factors determine how much old bone is resorbed and how much new bone is made. People have control over certain factors (such as diet) whereas others factors are beyond their control (such as age).

Most new bone is added during childhood and teenage years. Bone formation continues until the peak bone mass (maximum solidness and strength) is reached. Peak bone mass (or bone density) is reached around the age of 30. After the age of 30, bone resorption slowly begins to exceed new bone formation, which leads to bone loss (1). Bone loss in women occurs fastest in the first few years after menopause, but continues into old age. In men, bone loss usually occurs later in life compared to women. By the age of 65, men catch up with women and lose bone mass at the same rate.

Factors that can contribute to bone loss include having a diet low in certain micronutrients such as calcium and vitamin D, not exercising, smoking, long-term use of certain medications (e.g., corticosteroids) and low sex hormone (estrogen or testosterone) levels. Proper nutritional choices can help to preserve bone health. As people’s lifestyles and eating habits have changed over the years, many no longer receive adequate amounts of the essential bone-building nutrients. Thus appropriate dietary supplements and fortified foods are used to ensure sufficient intakes.

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Osteoporosis

Osteoporosis is a disease characterized by low bone mass and loss of bone tissue that may lead to weak and fragile bones. People with osteoporosis have an increased risk of broken (fractured) bones, particularly in the hip, spine and wrist (2). Without prevention or treatment, osteoporosis can progress without pain or symptoms until a bone breaks.

Osteoporosis is not just an “old woman’s disease.” Although it is more common in white or Asian women over the age of 50, osteoporosis can occur in almost any person, women and men, at any age. In women, bone loss can begin as early as age 25 years. 45% of fractures in women aged 50 and over are due to underlying osteoporosis (3). In fact, about 75 million people are currently affected by osteoporosis in the EU, USA and Japan alone (4). The estimated global direct cost of osteoporotic fractures is US$ 50 billion per year (3).

Building strong bones and reaching peak bone density (maximum strength and solidness), especially before the age of 30, can be the best defense against developing osteoporosis. Furthermore, a healthy lifestyle can keep bones strong, especially for people over the age of 30. Osteoporosis is more or less preventable for most people. Prevention is very important because, while treatments for osteoporosis are in place, currently no cure exists. Prevention of osteoporosis involves several aspects, including nutrition (see below) and exercise. Loss of muscle strength and mass, especially in the absence of physical activity, can reduce bone strength and stability, increasing the risk of falling and breaking a bone.

Early detection of low bone mass (osteopenia) or osteoporosis is the most important step for prevention and treatment. The only way to accurately test the strength and solidness of the bones is with bone mineral density (BMD) tests. Bone mineral density tests measure the solidness and mass (bone density) of bones in the spine, hip and/or wrist, which are the most common sites of fractures due to osteoporosis.

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Early prevention

Taking care of bone health already starts in childhood and adolescence. It is important to maximize the amount of bone tissue in the skeleton until the bones reach their peak strength and density around the age of 30. This peak bone mass is the ‘bone capital’ that is used through the rest of adult life. The most important nutrients that build peak bone mass are calcium and vitamin D (5, 6), with vitamin K, protein (7), phosphorus (phosphate), magnesium and zinc contributing as well (8). The benefits of healthy nutrient intakes on bone health are enhanced by regular physical exercise and a healthy lifestyle (9, 10).

Vitamin D deficiency and a lack of adequate calcium in diet may lead to rickets, a softening of bones in children, potentially leading to fractures and deformity. Rickets is among the most frequent childhood diseases in many developing regions but has resurged in developed countries as well (11-14). Achieving adequate dietary intakes of vitamin D in the key bone-building years is an urgent public health concern (15-17). Vitamin D is unique because it can be formed by the body with the right amount and intensity of sunlight on the skin. However, due to the use of sunscreens, dressing habits, indoor lifestyle and air pollution, vitamin D synthesis in skin is often severely limited. Several national pediatric associations now recommend that all infants consume at least 400 IU per day of vitamin D immediately after birth, continuing through adolescence, to make sure nutritional needs are met (18).

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Vitamin D and calcium

Calcium is the most important mineral bones, but it needs vitamin D to be absorbed by the body and incorporated into the bone. While all experts agree that the combination of these two micronutrients is essential for strong bones (1), the optimal nutrient dose is debated. In many countries dietary reference intakes are being considered for revision because of recent evidence that current recommendations are too low. Recently in the US, vitamin D intake recommendations were raised to 600 IU daily for 1 to 70 years of age and 800 IU after the age of 71 (19). Many experts suggest, however, that it takes a daily dose of at least 800 IU – two times higher than current EU recommendations – to bring vitamin D levels into an effective range (20-22). Some research indicates that 1,000-2,000 IU daily may be the optimum dose for bone health (23).

Bone fractures are not just due to brittle bones but also to falling. By minimizing the risk of falling, the fracture risk is reduced. Research indicates that vitamin D can help prevent fall-related fractures via its positive effect on muscle function and strength, which reduces loss of balance or swaying. Vitamin D plays a role in initiating protein synthesis in muscle fibers responsible for speed and strength – precisely those which help prevent a fall (24, 25). Muscle examined from people with vitamin D deficiency shows a breakdown in these fibers which can be reversed within a few weeks by increasing the amount of vitamin D in the body to sufficient levels (26). Furthermore, vitamin D helps maintain calcium levels in the blood, which is necessary for the normal functioning of muscles. Therefore vitamin D has a double impact on the prevention of osteoporotic fractures when the levels in the body are adequate: it strengthens bone and muscle at the same time, preventing osteoporosis, muscle weakness and fractures.

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Other micronutrients

Vitamin K is currently receiving attention in research for its role in bone health as it activates a protein that binds calcium into the structure of bone. Some clinical studies have shown a reduction in fractures, an increase in bone mineral density or signs that the bone formation has been boosted after vitamin K supplementation (27-29).

Vitamin C and vitamin B6 are needed to make collagen, an essential part of the organic material that holds bone together. Higher intakes of vitamin C may help to reduce bone loss (30).  A combination of vitamins B6, B12 and B9 (folic acid) may also help to decrease the risk of osteoporosis by reducing the concentration of homocysteine in the blood, which is thought to be associated with poor bone health (31).

The minerals magnesium and phosphorus as well as the trace element zinc are essential for building healthy bones. About half of all bone mineral is made up of phosphates, which forms a complex with calcium in the bone matrix. Both minerals have to be in balance because too much phosphate in the blood can lead to a removal of calcium from the bone (decalcification) and to a calcification of soft tissues, which can cause joint pain and skin alterations. Magnesium and zinc make up a minor part of bone minerals. Vitamins, minerals and trace elements work together to maintain healthy bones (1).
 
Emerging evidence suggests that fish consumption, or the long-chain omega-3 fatty acids it contains, may have bone-preserving properties (32). Oxidative stress can reduce the activity of cells responsible for bone building. Long-chain omega-3 fatty acids have been shown to have anti-inflammatory qualities and can potentially block the harmful effects of oxidative stress, which could increase bone formation.

References

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