NUTRITION

Looking after your Bone Health

Gillian Woodward

MOST athletes take great care of their muscles, but how often do they think of their bones? In this edition I want to draw attention to your bones and how to maintain their strength as the years progress. Recently the National Health and Medical Research Council announced new recommended dietary intakes of calcium for Australians. These new calcium guidelines have increased the daily intake target for all age groups over 9 years. An increase (since 1991) of about 300mg per day has been recommended for all adults and adolescents, so that most of us now need between 1000 and 1300 mg per day. The main reason for this increase in requirement of calcium is the growing number of Australians suffering from the disabling disease osteoporosis, which affects one in two women and one in three men over 60 years of age. Osteoporosis occurs when the bones become fragile due to the loss of calcium and other minerals, tending to fracture more easily. Of course this disease doesn’t just suddenly develop once you turn 60. It is due to a progressive loss of bone minerals. During the growth years of childhood and teens, calcium is most efficiently absorbed and stored so that a peak bone mass is reached in the early to mid- twenties. It is therefore most essential to consume adequate calcium during these years as well as to do regular physical activity, as this helps to keep the minerals within the bone tissue. Once women reach menopause, they rapidly lose bone minerals at a rate 2-4 times faster than before (due to a sharp decrease in oestrogen). Men start to gradually lose bone mineral in their 50’s. Eating enough calcium-rich food is important throughout this time of life, to help prevent excessive bone loss. The new RDI’s for calcium imply that most of us need to consume at least 3 serves of calcium-rich foods each day. Dairy foods provide the most readily available supply of calcium, as the phosphorus, lactose and vitamin D they contain all help us to absorb the mineral calcium. Vitamin D is also essential to good bone health as it aids calcium absorption. We need to expose our skin to sunlight regularly to activate the inactive form of vitamin D in our skin. In summer, six to eight minutes a day on most days is sufficient, but in winter, it should be half an hour most days. We need to have only 15 per cent of our body exposed - arms, hands and face - to get this exposure. However, people with dark skin need more as the pigments in their skin prevent the UV rays penetrating to the deeper layer of skin where vitamin D is made. Diet can also contribute some vitamin D, but the quantities are small. A few food sources include fish with a high fat content (like sardines, salmon, herring and mackerel), meat and eggs. In Australia, margarine and some milk and milk products (powdered milk, yoghurts and cheeses) are fortified with vitamin D. But these foods aren’t nearly enough to give us adequate vitamin D according to the experts, so we need some sun exposure as well. By the way, low vitamin D levels have also been linked to the incidence of cancer – especially breast, colon and prostate cancer. According to an editorial in the latest Medical Journal of Australia, nearly one third of men and women have mild to moderate vitamin D deficiency. Almost half of nursing home patients have at least mild Vitamin D deficiency (due mainly to lack of sun exposure). Eating too much salt, drinking excess alcohol and smoking are all lifestyle factors which increase our risk of developing osteoporosis. Likewise women who have early menopause and those who diet excessively to obtain low body weights are more at risk. Lack of weight-bearing physical activity is also a contributing factor, so keeping up the Orienteering and training can only help to counter this problem. How much dairy food do you need daily to achieve the new calcium intake targets? Three serves from the following: 250 ml milk (full cream or low fat), 200 g of yoghurt or two slices (40g) of cheese. Canned fish such as 100 g of salmon with the bones or 75 g (5) sardines also contains a similar dose of calcium as the above dairy serves – around the 300 mg mark. By using evaporated, reduced-fat milk in cooking instead of cream you will not only save on fat, but also gain 285 mg calcium per 100 ml. Buttermilk is also an excellent source with 360 mg per 250 ml glass. But before you go heading for the ice-cream tub with a large spoon, let me advise you that you would need to eat 8-10 scoops of it to obtain that 300 mg of calcium. Very enjoyable you might say, but what about your waistline? In case you are wondering about ‘milk substitutes’ like soy or rice drinks, which may indeed have been supplemented with calcium (because they don’t contain it naturally), there is evidence to suggest that calcium from these is not as readily absorbed as that from dairy foods. Calcium in the tablet form is also not as well absorbed as that from food, especially the dairy products. Some plant foods reported to contain calcium include broccoli, almonds and legumes. However, the oxalates and phytates in these foods reduce the uptake of calcium from them. To equal 1 glass of milk, we would need to eat 2.5 cups of broccoli, 5 cups of red kidney beans or 165g almonds – a huge amount of food. So while these foods add some extra calcium, it is best to rely on dairy foods for your main supply. In summary then, consume 3 serves of dairy food daily, get some sunlight on the skin regularly and keep up the physical activity of the weight–bearing kind (walking, running, Orienteering, tennis, golf, dancing, and resistance training - weights etc.). Go lightly on the alcohol and salt and most importantly, don’t smoke if you want to preserve healthy bones and avoid osteoporosis.

Gillian Woodward is a Practising Dietician and has been providing advice in the field for over 25 years. She has been an orienteer since 1984.