Bone health and nutrition

There are a number of dietary factors that are important in bone health:

1. Calcium
2. Vitamin D
3. Phosphorus
4. Sodium, Caffeine Protein
5. Alcohol
6. Potassium

1. Calcium

Calcium is the most important mineral of the skeleton. Approximately 1kg is contained within an adult skeleton. Like many areas of nutrition the answers are not clear cut, as there is much controversy surrounding bone health such as bone metabolism, calcium intake, calcium absorption (from the bowel), it is clear that calcium does have a very important role. Overall, there is some agreement that high calcium intakes (and indeed supplementation) are beneficial up to about 30 years of age when peak bone mass is thought to be achieved.

Eat foods that contain calcium that is easily absorbed. The more easily calcium is absorbed, the more available it is to be used by the body. It is well accepted that dairy products such as milk, cheese and yogurt are great sources of calcium because they contain high amounts of calcium, and the calcium is well absorbed by the body. Dairy products are also conveniently packaged, making them an ideal snack food for people on the go. Skim milk products provide as much calcium as wholemilk with the added advantages of less fat. Vegetables such as broccoli, cabbage greens and Brussel sprouts, as well as the edible bones in fish (e.g. tinned salmon and sardines) also contain calcium. Vegetables, however, contain smaller quantities of calcium per serving than dairy foods. It is possible for foods to contain calcium and for that calcium to have limited availability to the body. The reason is that these foods contain calcium-binding substances called oxalates (found in many green vegetables) or phytates (found in unleavened grain products). Milk and milk products do not contain phytates or oxalates. Of these two substances, oxalates are considered more potent in their ability to restrict calcium absorption. While spinach contains calcium, it also contains oxalates making the calcium less useful. Even though the substances contained in these foods inhibit calcium absorption, experts agree that the benefits you derive from the other important nutrients such as Vitamin C, folate, magnesium etc contained in this group of foods far outweigh the negative effects of their tendency to block calcium absorption.

Click here to download a table of Calcium content of foods

Heaney, R. P. "Skeletal Development and Maintenance: the Role of Calcium and Vitamin D." Adv Endocrinol Metab 6 (1995): 17-38.
Matkovic, V (1991). Calcium metabolism and calcium requirements during skeletal modelling and consolidation of bone mass. American Journal of Clinical Nutrition, 54:245S-259S.
Matkovic, V. and R. P. Heaney. "Calcium Balance During Human Growth: Evidence for Threshold Behavior." American Journal of Clinical Nutrition 55, no. 5 (May 1992): 992-996.
Anderson, J. J. and J. A. Metz. "Contributions of Dietary Calcium and Physical Activity to Primary Prevention of Osteoporosis in Females." Journal of the American College of Nutrition 12, no. 4 (August 1993): 378-83

2. Vitamin D

Vitamin D can be obtained from food such as eggs, whole milk and fortified low fat milks, butter, margarine, liver, liver pate, oily fish (mackerel, kippers, salmon, trout). You can also get it from sunlight ­ the body makes Vitamin D by a process initiated by ultra-violet light on the skin. Along with a hormone called parathyroid hormone and calcium, Vitamin D regulates calcium and phosphorus metabolism and promotes the absorption of calcium from the gut and kidney. Vitamin D levels fall with age and vary with the season, but it is not clear whether all age groups would benefit from additional Vitamin.
What is clear is that Vitamin D is an essential nutrient and that athletes should ensure that their diet includes sources of Vitamin D ­ both dietary and from normal exposure to sunlight.

3. Phosphorus

Phosphorus is as important for bone health as calcium. Present in the body as phosphate, it makes up about half the weight of bone mineral. The diet must provide sufficient amounts of phosphorus, along with calcium, to mineralise and maintain the skeleton. However, phosphorus is present in all plant and animal protein and so inadequate intakes of phosphorus are not commonly seen, except in the elderly population. Phosphates are also added to cola-type drinks to regulate the acidity, and to processed meats and frozen poultry to keep the food moist. So the problem for most people, including athletes, may be that they are getting too much, rather than too little, phosphorus particularly if drinking a great deal of soft drinks. Too much phosphorus may lead to a reduction in the absorption of calcium and indeed magnesium, another essential mineral.

To date, very few studies have found harmful effects of excess phosphorus intake on bone health in humans. Despite its effects on the absorption of calcium, Phosphorus reduces the amount of calcium lost in the urine. This would make sense as phosphorus rich foods are often good sources of calcium e.g. milk and milk products Overall, Phosphorus is an essential mineral that is vital in bone health. Its requirements are usually set as to equal calcium e.g. 600mg Calcium : 600mg Phosphorus. A very high intake of Phosphorus from foods low in calcium e.g. soft drinks and certain manufactured foods or through Phosphorus-containing dietary supplements may not be beneficial to bone health. A maximum amount per day has been set by the World Health Organisation in 1982, at 70mg Phosphorus per kg of bodyweight.

4. Sodium, Caffeine and Protein

Pay attention to foods that cause calcium loss through the urine. You lose calcium daily through the urine. While a certain amount is perfectly natural, there is evidence to suggest that calcium loss through the urine is increased by excess consumption of salt, caffeine and protein.
Salt (Sodium) - in excess has been shown to increase the loss of calcium through the urine. Over 90% of sodium in our diets comes from manufactured food rather than from salt added to food at the table or during cooking. Athletes should be advised that food items that are low in essential nutrients yet high in salt such as crisps, tinned and packet soup, 'instant meals', should be kept to a minimum. Foods higher in salt that also contain important nutrients for health and performance should still be included e.g. milk, cheese, bread, breakfast cereal, tinned fish, baked beans. Your sports drink is likely to contain salt/sodium to help rehydrate you more quickly ­ you should continue to use these drinks unless otherwise advised by a qualified sports dietitian or doctor.

Caffeine - is contained in many beverages, including coffee, tea, cola and certain energy drinks. Recent studies show that caffeine increases calcium loss through the urine. Most experts agree that two to three cups a day is probably not detrimental provided that calcium intake is adequate. If you consume more than three cups in a day, a good rule of thumb is to have at least one glass of milk for every cup of coffee (or to make some of those coffees café lattés or cappuccinos). Keep in mind that the less calcium in your diet, the more serious the effects of caffeine on this calcium loss.

Protein - when consumed in excessive amounts, has been shown in short term studies to increase the amount of calcium that is lost in the urine (Phosporus helps prevent urinary calcium losses). However, protein foods (meat, fish, poultry, dairy products, tofu, dried peas, beans, etc.) contain many important nutrients such as calcium, iron, zinc, B1 and B2, so they should not be cut out of the diet. In the long term the effects of a high protein diet on bone health have yet to be decided. In terms of bone health, taking high protein supplements as drinks or bars is not advisable, whereas a good intake of protein-rich foods such as meat, fish, nuts, milk and beans to meet requirements for training and recovery is essential.

5. Alcohol

Excessive alcohol intake, such as seen in alcoholic, is associated with osteoporosis and fractures associated with osteoporosis. Alcohol is toxic to bone-forming cells and may interfere with bone metabolism. When considering moderate alcohol intake, the picture is not quite o clear. Both positive and negative effects have been reported, thought to be linked in with hormone levels. It is likely that in the future scientists will be able to say with better confidence that a threshold of alcohol intake exists.
Serious athletes moderate their alcohol intake if performing consistently at a high level. Too much alcohol will interfere with hydration, carbohydrate metabolism including blood glucose levels, the immune system and the body's ability to repair itself generally. As a football player once reminded me:

6. Potassium

Potassium, as potassium bicarbonate, is a nutrient which has appeared in the research as late for its beneficial effects on mineral balance and bone health. The body's acid:alkali balance can respond to both blood and plasma bicarbonate concentrations. Some experts believe that the failure to keep the acid:alkali balance may be the way in which adults show a slow bone loss as they get older. Calcium salts (alkaline) are released from bone in response to higher acidity levels, such as those which may be generated from acid-producing foods, such as meat. Therefore, there may be an argument for eating alkali-forming foods such as fruit and vegetables for long-term bone health. Both a high potassium diet and potassium bicarbonate have been shown to improve calcium balance in healthy young adults. For good bone health it therefore seems wise to eat plenty of potassium-rich foods. Rich sources of potassium include fruit and vegetables such as oranges, bananas, potatoes, seeds, nuts, milk, avocados, mushrooms and tomatoes.
Another reason for those involved in sport to eat fruit and vegetables!