Calcium Needs during the Growth Spurt and Low Bone Density
Last week we looked at skeletal growth and the factors that influence skeletal growth particularly during the adolescent stage. Two of the factors affecting skeletal growth are physical activity and nutrition, specifically the need for calcium. We looked at calcium sources, the amount of calcium needed and how calcium is absorbed.
In this article we help you understand that there may be reasons why sufficient calcium might not be taken in so that you can encourage your adolescents to follow appropriate nutritional practices.
Finally we provide you with a practical summary to maximise calcium intake and ensure optimal bone growth and health.
BARRIERS TO ADEQUATE CALCIUM INTAKE AND ABSORPTION
Young female athletes who restrict energy intake tend also to restrict dairy products and thus are at a risk of low calcium intakes. (1,3) This is based on the misconception that all dairy foods are fattening. The truth is however that low-fat or fat-free milk and milk products contain at least as much calcium as full-cream milk and can therefore be part of a successful weight loss or weight maintenance program. (2)
Adolescents usually start consuming greater amounts of soft drinks and other cold drinks at the cost of milk intake. Soft-drink consumption peaks in adolescence, at which time milk intake is at its lowest level. (2) In addition, high intakes of caffeine and salt (found mainly in processed foods) increase loss of calcium in the urine and thus prevent it being absorbed into the cells where it is needed and used.
Some individuals avoid the intake of dairy products due to lactose intolerance. The truth is although that many children with lactose intolerance can drink small amounts of milk without discomfort, especially when accompanied by other foods. Other alternatives include the use of fermented dairy products such as hard cheese and yoghurt, which may be tolerated better than milk. Lactose-free and low-lactose milks are available. Non-dairy food products (such as certain vegetables) or calcium-supplemented foods (including calcium-fortified soy milk) may be used as other calcium sources. (2)
Another potential barrier to calcium absorption is alcohol. Alcohol also increases urinary losses of calcium and can lead to decreased serum vitamin D levels, resulting in malabsorption of calcium from the small intestine. (4)
WHEN ARE CALCIUM SUPPLEMENTS REQUIRED?
Supplements should be considered for children and adolescents who cannot or will not consume adequate amounts of calcium from preferred dietary sources. Supplements most often contain calcium carbonate and supply 300 to 600 mg of elemental calcium per tablet. Remember to check the “elemental calcium” amount per tablet. Some mineral supplements also contain vitamin D.
Decisions about their use must be made on an individual basis, keeping in mind the usual dietary habits of the person, any individual risk factors for osteoporosis and the likelihood that the use of the supplement will be maintained. (2). Absorption of calcium reaches a plateau at doses of about 500 mg. Calcium carbonate tablets should ideally be taken with food. Doses spaced throughout the day appear to result in a greater total calcium absorption than if one large dose is taken only once during the day. (3)
1. Bass S & Inge K. Nutrition for special populations: Children and young athletes in Bourke Clinical Sports Nutrition
2. Greer FR & Krebs NF. (2006) Optimizing Bone Health and Calcium Intakes of Infants, Children and Adolescents. Am Acad Ped 117:578 – 585.
3. Burke LM, Castell LM, Stear SJ et al. (2010) A – Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance Part 7. Br J Sports Med 44:389 – 391.
4. Micklesfield, L. Bone Physiology. Lecture notes, UCT.