骨質疏鬆

同事問我有關骨質疏鬆的問題。

其中一個預防的方法，自然是做力量訓練的運動（例如舉重和瑜伽）。

當然，營養更重要。因為它是每天賴以生存的元素。

想著想著，不如把心一橫，將自己修讀的營養學某些關於這個問題的解釋，post在這裡吧，等大家知多一點，做足防避：

Osteoporosis is defined as low bone mass density (BMD). The common perception is that osteoporosis is a problem mainly affecting post-menopausal women, caused by a reduction in oestrogen and a lack of calcium. Analyses of skeletal remains from varying cultures show that post-menopausal women didn’t routinely suffer from decreased bone density, it’s a recent phenomenon, mainly of Western society. In some countries more men than women are sufferers. Some primitive civilisations have low calcium intake but virtually no osteoporosis while Inuits consume vast amounts of calcium but have a high incidence.


Bones are constantly being renewed - osteoblasts are cells that promote growth and osteoclasts absorb old bone tissue. Oestrogen (the chief component of HRT medication) stimulates osteoclasts but does nothing to lay down new bone cells. Progesterone and the male hormone testosterone stimulates osteoblasts to build new bone. Most women and men will suffer some bone loss as they age, BMD starts to decline at around 35 years of age (when oestrogen levels are high), but serious bone loss isn’t inevitable, nor does lowered BMD mean the individual is going to suffer bone fractures.


It’s unlikely that oestrogen and calcium alone are the most significant factors to bone health. Differences in lifestyle, what we eat, or don’t eat are also crucial elements. Regular weight-bearing exercise helps to increase bone density, while sedentary people are likely to lose bone mass. Bone-dissolving substances include excess protein, saturated fats, sugar, sodium chloride, drugs, alcohol, caffeine, tobacco, prolonged stress, free radicals and lack of exercise.


The effects of diet on bone integrity

Digested food leaves a residue that is acid or alkali. Fruits, including citrus, and vegetables are alkaline-forming, while animal proteins such as dairy products, meat and fish are acid-forming. An over-acidic diet leaches neutralising alkaline agents, sodium and calcium, from bone - vegetarians tend to have less risk of osteoporosis. While calcium is vital for the development and maintenance of healthy bones, there are other essential nutrients. The body automatically regulates the balance of minerals so although milk provides calcium, a diet high in cows’ milk products can precipitate a deficiency of other vital minerals, such as magnesium. Excess phosphate, found in many processed foods and drinks (as phosphoric acid), may cause the body to compensate by drawing calcium from bones. Children who drink several glasses of phosphate-containing drinks a day are at risk of developing low blood calcium levels.


Good sources of many minerals include green leafy vegetables, pulses, seeds and nuts. Although pulses are good sources of proteins and nutrients, they contain phytates (naturally occurring chemicals) that can bind to all minerals, making them less available for absorption. As adequate protein is vital for bone health, the aim should be for a metabolically balanced diet, with neither excess carbohydrates nor proteins.


Fear of insufficient calcium intake has become an obsession but the body’s metabolism of this mineral is poorly understood. Although we may take in sufficient dietary amounts, it’s not necessarily deposited in bones because adequate stomach acid, magnesium and vitamin D are needed for calcium absorption. With inefficient metabolism you can have too much calcium circulating in the blood. This can lead to calcium deposits, presenting problems such as kidney stones and irritative crystals in arteries (arteriosclerosis) and joints (arthritis). In this situation, supplementing calcium will make things worse. The recommended daily intake of calcium (500-1000mg) is not difficult to reach. Sesame seeds, almonds and green leafy vegetables are equally good sources as milk and are more readily absorbed than calcium supplements.


A number of organisations offer bone density tests. The results are likely to indicate decreased BMD but as density starts to diminish in middle age, such results are relatively normal. Advice following these tests is generally to take calcium supplements. However, modern research demonstrates that intake levels of more than 800mg daily may be unnecessary for maintaining calcium metabolism if vitamin D status is adequate and it’s suggested that vitamin D sufficiency may be more important than high calcium intake.