Healthy bones

We often think about how we can be faster, stronger or go further and this involves developing muscle mass, however we also need to think about the skeletal structure that supports the muscles.  It also needs to be strong and remain strong.

Bone

Bone consists of an organic matrix, primarily collagen fibres, around which salts of calcium and phosphate are deposited in combination with hydroxyl ions in crystals of hydroxyapatite.  The tensile capacity of collagen and the compressional ability of calcium salts combine to give bone its strength.

The largest part of the skeleton (80%) is made up of compact cortical bone.  The remainder is the trabecular bone that occurs in the knobbly ends of the long bones, the iliac crest of the pelvis, the carpel bones of the wrist, scapulae and vertebrae.  Trabecular bone is spongy and less dense than cortical bone, and these are the areas that most osteoporotic fractures occur in later life.

Osteoporosis

Osteoporosis is characterized by low bone mass and microarchitectural deterioration of bone, leading to enhanced bone fragility and a consequent increase in fracture risk.  Osteoporosis is a major public health problem involving postmenopausal women and ageing individuals.

Are Some Sportswomen More at Risk of Developing Osteoporosis?

In general, women who are slim, of Caucasian or Asian ethnicity, smoke, do not exercise regularly, have irregular menstrual periods or early menopause, are at highest risk of developing osteoporosis.  Among sportswomen, those most at risk are those who become amenorrhoeic (have no menstrual period for 3 months or longer).  The decreased oestrogen levels associated with amenorrhoea causes increased bone loss, despite the positive effects of physical activity on bone density.  Not all amenorrhoeic athletes have low bone density.  However, prolonged amenorrhoea (no menstrual period for six months or longer) may result in low bone density and therefore ‘early onset' osteoporosis (weak bones and fractures occurring at a young age) and an increase incidence of stress fractures.  Other factors include training patterns and body composition may also contribute to injuries and stress fractures.  Athletes who are on energy restricted diets (intentionally or unintentionally) are at increased risk due to a low calcium intake in the diet; calcium is important for maintenance of skeletal mass.  In addition a low energy intake has been reported to be a possible cause of amenorrhoea that results in loss of calcium from the bone and weaker bone structure.  Some medical conditions (eg thyroid disease) and medications (eg corticosteroid medicines) are also associated with an increased risk.

Prevention of Osteoporosis in Sportswomen

The best way to develop the highest possible peak bone density is during childhood and adolescence and maintaining menstrual cycles and a high dietary intake of calcium during adulthood.  The schematic diagram below shows bone mass and fracture risk throughout the lifecycle.

If menstrual cycles do stop for any length of time then it is important you see your sports physician and discuss this.  They may prescribe ‘hormone replacement' or the contraceptive pill to prevent further bone loss.

It is also important that you include plenty of calcium in your diet. A Survey in 1997 found that none of the females age groups met the recommended intake for their age, and the older men also failed to meet their recommended intake.

Sources of Calcium in the Diet

Calcium is mainly found in dairy products and fortified cereals.  It is also found in smaller amounts in green leafy vegetables, cereals, nuts and dried fruit – see the table below.  It is important you include a variety of these in your diet each day.

By including plenty of calcium containing foods in your diet, ensuring you maintain normal menstrual functioning, limiting alcohol intake, not smoking and participating in regular weight-bearing exercise you are doing all you can to prevent low bone density and increased risk of stress fractures and osteoporosis.

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