Ensuring children and adolescents build up strong bones is key to their present and future health. Paediatric dietitian Judy More introduces a new series to put bone health high on health professionals' agenda

Judy More BSc RD RNutr  Freelance Paediatric Dietitian, London 

ABSTRACT
 

One in two women and one in five men suffer from osteoporotic fractures after the age of 50. Enabling children and young people to develop strong bones and achieve their maximum potential bone mass will help prevent undue bone loss and osteoporosis in later life.
Although 70-80% of peak bone mass is genetically determined, the remainder is determined by dietary and environmental factors. The most important dietary factor for bone health is calcium, which in the UK is obtained mainly from dairy foods (45%) and cerealbased foods (27%). In the UK one-quarter of teenage girls consume insufficient calcium to meet their minimum dietary requirements. The majority of teenage boys and girls fail to meet the UK Government's targets for calcium intakes. This is an important public health issue as 90% of peak bone mass is attained by the age of approximately 18 years in girls and 20 years in boys. Health professionals need to be aware of the importance of childhood and adolescence for building healthy bones and to work with this age group to promote the dietary and lifestyle factors that contribute to bone health and peak bone mass. They could usefully include advice on including three helpings of calcium in the diet each day, as highlighted in the current "3-a- Day" campaign.
Journal of Family Health Care 2008; 18(1): 22-24

Key points   
_ Childhood and adolescence are key periods for building up strong bones to reduce the risk of osteoporosis in later life
_ Achieving and protecting bone mass is central to bone health throughout life
_ 90% of peak bone mass is achieved by around the age of 18 years for girls and 20 years for boys
_ Although genes play a large part in determining an individual's bone mass, 20 to 30% of peak bone mass depends on the quality of diet and lifestyle
_ Key factors include an adequate intake of calcium in the diet, adequate vitamin D status, weight-bearing activity and avoiding smoking and excessive alcohol consumption
_ One in four teenage girls fail to consume the minimum daily calcium requirement, placing themselves at high risk of osteoporosis in later life. The majority of teenage boys and girls fail to meet the UK Government's targets for calcium intakes
_ Most calcium (45% of intake) in the UK diet comes from milk and milk products, with cerealbased products contributing 27%.
The calcium in dairy foods is the most easily absorbed by the body Children's health and nutrition are important issues for most health care professionals and parents. But, apart from obesity and Jamie Oliver's criticisms of the poor quality of school dinners, children's nutrition seldom makes the headlines. Yet there are serious issues that need tackling, particularly bone health. A series of articles in Journal of Family Health Care this year will discuss the latest nutrition and lifestyle advice for improving health and quality of life from early childhood to adult life. This first article will focus on bone health, calcium needs and how healthy lifestyles during childhood can reduce the risk and severity of osteoporosis in later life.

The impact of osteoporosis in the UK 
_ One in two women and one in five men will suffer from osteoporotic fractures after the age of 501. For women, this risk is greater than that for cancer or cardiovascular disease (World Health Organization Study Group)2.
_ There are approximately 230,000 fractures per year in the UK, with a cost to the NHS in excess of £1.7 billion3. With a growing elderly population, the projected rise in osteoporosis suggests escalating financial costs in the future4.

Childhood is a key time for reducing the risk of osteoporosis   
If children build up strong bones in childhood they will reduce their risk of osteoporosis later in life. Three key mechanisms are involved in determining bone health3,5:
1. Optimising bone mass during childhood and adolescence in order to achieve peak bone mass. (Peak bone mass is the stage at which a person's bones reach their maximum density and strength.) 70-80% of peak bone mass is governed by a person's genes. The remainder is determined by diet and lifestyle at critical times of growth and development
2. Maintaining peak bone mass during early adulthood
3. Minimising bone loss in later life. Achieving and protecting peak bone mass is central to bone health throughout life.

What is bone?   
Bone is a living tissue, continually replacing old with new. During periods of growth, i.e. childhood and adolescence, the rate of new bone formation is greater than bone breakdown (depending on adequacy of diet and lifestyle). This produces a net result of increased bone size. For each child the aim is to reach their peak bone mass, which is their genetically determined maximum bone mass potential3,5,6. After our mid-30s and possibly 40s, the rate of bone loss dominates, resulting in a reduction in bone density3,5. The rate of loss will depend on many factors including original reserves attained during childhood and adolescence, and dietary and lifestyle habits4,7.

Maximising bone mass in children and adolescents 
Bone mass and strength develop during periods of growth and development. It is important to realise that 90% of peak bone mass is achieved by around the age of 18 years for girls and 20 years for boys when growth usually ceases. The remaining 10% of peak bone mass is accrued at a slower rate, into the third decade of life3,5. Growth spurts during childhood and adolescence result in accelerated bone mass. About 37% of peak bone mass accrues during the pubertal growth spurt5.

Can diet and lifestyle significantly influence bone strength?   
Between 20% and 30% of peak bone mass is dependent on the quality of diet and lifestyle. The key dietary and lifestyle factors that influence peak bone mass have been identified as3,5,6,7:
_ Adequate calcium intake
_ Adequate vitamin D status
_ Adequate weight-bearing activity
_ Appropriate body weight
_ Adequate intakes of protein, phosphorus, magnesium, fluoride, vitamin C, vitamin K, copper, manganese, zinc and iron
_ Avoiding smoking and excessive alcohol consumption. In case this may appear not to apply to children, we need to be aware that:
_ 10% of 11-15 year olds were reported to be regular smokers in 20028
_ A Government survey in 2004 revealed that 23% of 11-15 year olds consumed alcohol (average intake 10.5 units per week)9.

Calcium - the key to bone strength   
Calcium is the most abundant mineral in the human body and 99% is found in bones and teeth6,7. Between birth and maturity, bone calcium content increases from 30 g to around 1200 g6. Calcium and phosphorous are the main minerals for bone strength as they are deposited into the porous protein structure of bone, thereby increasing density and therefore strength3,5,7,10. Phosphorous is abundant in many foods but adequate amounts of calcium are not always eaten. This makes calcium the critical dietary factor for bone health4,6,7,10.

Absorbing calcium from the gutVitamin D   
Is essential for absorbing adequate calcium from food but national surveys have shown that many individuals have very low levels of vitamin D and need supplements. Those with low levels only absorb about 15% of calcium in their food while those with normal levels absorb up to 40%11. Apart from breast milk, calcium in dairy foodsbone health 1 is the most easily absorbed by the body. Dairy products also contribute other nutrients associated with better bone strength, such as protein, phosphorus and zinc.
Calcium absorption increases at times when it is most needed - during childhood growth spurts and especially adolescence in both boys and girls5,6,7.
_ In girls, calcium absorption reduces within 2-3 years of menarche
_ For boys, higher calcium absorption occurs up to the age of about 18 years.

Do UK children eat enough calcium?   
Table 1 shows the range of recommended daily calcium intakes for different age groups12. In Table 1, "Lower Reference Nutrient Intake (LRNI)" reflects the quantity of calcium which will meet the needs for less than 5% of the UK population. Populations not meeting these requirements will be at high risk of poor peak bone mass and osteoporotic fractures. "Reference Nutrient Intake (RNI)" reflects the quantity of calcium expected to meet the needs of the majority of the UK recommendation and used for target intakes, i.e. what most people should be aiming at in their diets.
The figures in Table 1 are taken from national surveys in the UK and show that while children up to the age of 10 years eat adequate amounbone health 2ts of calcium, adolescents do not13. Our adolescents are not taking advantage of the last window of opportunity to optimise their bone mass. One-quarter of teenage girls are failing to consume the minimum calcium needs and are placing themselves at high risk of osteoporosis in later life. The majority of teenage boys and girls fail to meet the UK Government's target intakes for calcium.
bone health 3
A practical approach to meeting calcium needs - 3-a-Day14    
Most calcium (45% of intake) in the UK diet comes from milk and milk products. Cereal-based products also make a significant contribution (27% of calcium intake): white and brown flours used in bread and most breakfast cereals are fortified with calcium. Table 2 gives examples of foods containing calcium.
The Dairy Council UK has jointly launched the 3- a-Day campaign with the US and Irish Dairy Councils to help health professionals give a simple practical public health message on eating enough calcium.
The message is to have three daily servings of milk, cheese or yoghurt. Each serving of milk, yoghurt or cheese will meet one-third of the UK recommended calcium intakes (RNI). As different age groups have different calcium requirements, serving sizes of portions will increase as children grow (see Table 3).
bone health 4
Non-dairy alternatives providing calcium 
There are some non-dairy options that can also significantly contribute to calcium intake (see Table
4
). Oily fish with soft bones, white/brown bread, fortified soya products and nuts can all contribute significantly. However, apart from bread, they are not foods that children would eat regularly three times a day.
Children who have a milk allergy or lactose intolerance, or follow a restrictive or vegan diet, should be referred to a registered paediatric dietitian for specialist advice on achieving an adequate calcium intake.

References   
1. Van Staa TP, Dennison EM, Leufkens HG, Cooper C. Epidemiology of fractures in England and Wales. Bone 2001; 29(6): 517-522
2. World Health Organization Study Group. Assessment of Fracture Risk and Its Application to Screening and Postmenopausal Osteoporosis. Report of a WHO Study Group. Technical Report Series No. 84. Geneva: WHO, 1994
3. Lanham-New S, Thompson RL, More J, Brooke-Wavell K, Hunking P, Medici E. Importance of vitamin D, calcium and exercise to bone health with specific reference to children and adolescents. Nutrition Bulletin 2007; 32(4):364-377
4. World Health Organization Scientific Group. Prevention and Management of Osteoporosis. Report of a WHO Scientific Group. Technical Report Series No. 921. Geneva: WHO, 2003
5. Heaney RP, Abrams S, Dawson-Hughes B et al. Peak bone mass. Osteoporosis International 2000; 11(12): 985-1009
6. Theobald HE. Dietary calcium and health. Nutrition Bulletin 2005; 30(3): 237-277
7. Department of Health. Nutrition and bone health: with particular reference to calcium and vitamin D. Report of the Subgroup on Bone Health (Working Group on the Nutritional Status of the Population of the Committee on Medical Aspects of Food and Nutrition Policy). Report on Health and Social Subjects No. 49. London: The Stationery Office, 1998
8. Boreham R, McManus S (eds). Smoking, Drinking and Drug Use among Young People in England in 2002. London: National Centre for Social Research 2002
9. National Centre for Social Research and National Foundation for Educational Research. Fuller E, Bates B, Benkinsop S et al. Smoking, Drinking and Drug Use among Young People in England in 2004. London: Department of Health, 2005
10. Heaney RP, Weaver CM. Newer perspectives on calcium nutrition and bone quality. Journal of the American College of Nutrition 2005; 24 (6 Suppl): 574S-581S
11. Holick MF. Vitamin D deficiency. New England Journal of Medicine 2007; 357(3): 266-281
12. Department of Health. Panel on Dietary Reference Values of the Committee of Medical Policy of Food Policy. Dietary Reference Values for Food Energy and Nutrients for the UK. Report on Health and Social Subjects No. 41. London: Her Majesty's Stationery Office, 1991
13. Gregory J, Lowe S, Bates CJ et al. National Diet and Nutrition Survey: Young People Aged 4-18 years. Vol. 1. Report of the Diet and Nutrition Survey. London: The Stationery Office, 2000
14. McKinley M. A new health promotion message for dairy - the 3-A-Day campaign. Nutrition Bulletin 28(4): 369-372 15. Food Standards Agency. McCance and Widdowson's The Composition of Foods. 6th summary edition. Cambridge: Royal Society of Chemistry, 1991