Posted by kathryn in Nutrition

In parts one and two of this series, I covered the basics on bones: what they are and why we need them. I also looked at calcium, why it’s important for our health and touched on the debate over how much we need.

Healthy bones are important as they allow us to continue leading active and healthy lives into old age. The weakening of bones that occurs with osteoporosis, is debilitating and something we all want to avoid.

1. The importance of exercise

The number one, most important thing for the health of your bones is to get regular exercise. Physical activity strains and stresses your bones. Cells within the bones react by making them stronger and denser. Regular physical activity makes it possible to retain and possibly even increase bone density. Exercise also improves balance, thereby reducing the risk of falls and resultant fractures.

For the activity to help your bones though, it must be weight-bearing and you must vary the activity. Different forms of exercise stress different bones, hence the need for variety. Good forms of exercise for bone health include jogging, yoga, jumping, stair climbing and weight training.

2. Getting enough calcium

It’s important your diet includes enough calcium. Inadequate calcium intake will prevent bones from becoming denser (in response to exercise) and will lead to calcium leaching from your bone stores to be put to other uses. The difficulty here though is, how much is enough?

The current Australian RDI is 1,000mg for most adults and 1,300mg per day for menopausal women. In contrast, a 1991 British review found that 700mg per day was enough for healthy bones, while intake can be as low as 300mg per day in Japan, India and Peru. On the other hand, in randomised controlled trials individuals have benefitted from increasing their calcium intake from 500 – 900mg to 1,500mg per day.

There is no evidence that calcium alone stimulates bone growth. If you are physically active and your bones are regularly stressed, then calcium can be used to make stronger bone tissue. However simply eating bucketloads of calcium is not going to make your bones stronger.

In the absence of a definitive answer on how much calcium is enough, my best judgement is to aim for about 700mg per day. For non-vegans and the lactose tolerant, this can be achieved through one or two serves of dairy, in combination with a healthy diet. For non-dairy people, there are more sources here.

3. Getting enough vitamins A, D and K

Vitamin D encourages greater calcium absorption from your food and minimises the amount lost in urine. Vitamin K is involved in your body’s regulation of calcium and in bone formation, while Vitamin A directs the process of borrowing and then re-depositing calcium from bones.

Here in Australia vitamin D is rarely a problem, as your body manufactures it in response to sunlight. Vitamin K is found in green, leafy vegetables such as broccoli, spinach, silverbeet, Brussels sprouts, kale and dark green lettuces.

While adequate vitamin A is important for bone health, it’s equally as important not to have too much. Vitamin A can be found in liver, whole milk, cheese and butter. It can also be manufactured by our body from the carotenes from carrots, dark green leafy vegetables and orange coloured fruits, like mangoes and apricots.

4. Avoid too much protein

While the exact nature of the relationship between excess protein and bones is unclear, there is evidence that too much protein leads to calcium being leached from your bones. Animal protein seems to be cause more problems than vegetarian sources.

Protein intake is calciulated on an individual basis, with the generally recommended level for most people being 0.75g of protein per kilogram of body weight. Excess protein is considered to be more than 2g of protein per kilogram of body weight.

Bone health: the series

This is the final post in a three-part series on bone health. The other two can be found at:

• Bone health I: what are bones?
• Bone health II: the calcium debate

27 July, 2007