Bone, a living tissue, is constantly remodelling. In a healthy individual, formation exceeds loss until the third decade, when peak bone mass is reached. A slow rate of loss is then normal for both genders.
During the menopause in females, there is a significant loss of bone for up to 15 years, then the rate of loss slows again.
The higher the peak bone mass attained, the higher the bone mass is likely to be later in life. Hence it is vital to focus efforts on the promotion of healthy bones in children and adolescents through nutrition, activity and the management of chronic disease.
The principal reasons for limited peak bone mass include poor nutrition, inactivity or excessive activity, and diseases (rheumatological or endocrine, malabsorption syndromes and anorexia nervosa). Genetic factors also play a part and account for 70% of variability in peak bone mass achieved.
Nutrition in children
Adequate calcium, vitamin D and calories are vital to bone health. Calcium deficiency is common among children and teenagers, as consumption of milk and dairy products has waned over recent decades.
Vitamin D deficiency has re-emerged as a public health problem, increasing the risk of osteomalacia and reduced peak bone mass. Sunshine is the main source of vitamin D, but in northern Europe, there is inadequate sunlight for cutaneous conversion to the active moiety.
Only a few natural foods, such as oily fish and eggs (20-40 units per egg), contain significant amounts of vitamin D. In the UK there are few fortified foods (breakfast cereals and margarine) and these contain only a small amount of vitamin D. All formula milks are fortified, but cow's milk is not fortified in the UK.
There is some debate as to the definition of vitamin D deficiency or insufficiency, but most groups suggest a level of <25nmol/L to define deficiency and 25-50nmol/L to define insufficiency.
Pregnant and breastfeeding women should take a daily supplement containing 400 IU (10 microgram) vitamin D. Newborns up to one month old should be given 300-400 IU per day, and those aged one month to 18 years should have a daily intake of 400-1,000 IU.
Deficiency should be treated for four to eight weeks as follows: up to six months old, 1,000 IU daily, six months to 12 years, 6,000 IU daily, and 12-18 years, 10,000 IU daily.
Other nutritional problems that lead to bone health impairment include calorie restriction, in particular anorexia nervosa. This has complicated effects on bone, owing to delayed menarche, amenorrhoea, leptin deficiency and negative effects on the hypothalamic-pituitary axis, and other metabolic and hormonal imbalances.
Nutrition in adults
The recommended daily calcium intake from diet and supplements combined is 1,000mg per day for people aged 19-50 years and 1,200mg per day for those aged over 50.
The most effective method for meeting this recommendation is by diet. Supplements should only be used if necessary. Excessive calcium intake will not provide added benefit and can cause adverse effects.
Supplements should be taken with food and water, spaced out over the day if necessary, as ≤600mg is absorbed at any one time.
Suboptimal vitamin D levels are common in adults. A serum 25-OHD level >50nmol/L (preferably 75-100nmol/L) should be the target.
Supplementation if needed is usually with cholecalciferol (D3); D2 is used in vegetarians. It should be taken with a meal containing some fat to ensure absorption. Response varies substantially and higher doses are needed in obese subjects.
Nutritional factors include adequate calories and protein. Adequate protein intake is needed to achieve peak bone mass in childhood and maintain healthy bone in adulthood. The recommended daily intake of phosphorus, vitamin K and magnesium is also important in bone metabolism.
Children who perform regular weight-bearing exercise have higher bone mass than those who do not. Activities that are good for bone development involve some plyometric activities, such as gymnastics, skipping and running.
These result in high-intensity loading forces that augment bone mineral accrual in children and adolescents, not just through direct effect on bone, but also through muscular development that places tensile stress across the bone, enhancing its development.
In adults, activities that include vertical impacts are recommended to promote bone health (running, jumping, power-walking, some dance regimens, racquet sports). Patients with osteoporosis need a customised regimen. High-impact or explosive activities and heavy weights are contraindicated. All patients should have additional postural and proprioceptive training.
Those who exercise intensively may also be at risk. This is particularly true in lightweight sports and is most commonly a problem in females. Management of these patients is challenging and referral to a specialist is recommended.
Assessment in children
Any child who has sustained a fragility fracture or is considered at increased risk of fracture should be referred to a rheumatologist or metabolic bone physician.
DXA is part of the assessment of skeletal health for this age group.
In young people, management of low bone mass is primarily through managing associated diseases and optimising nutrition and exercise. The use of bisphosphonates and other agents is on a case-by-case basis under specialist care.
Assessment in adults
Osteoporosis is the end result of a progressive loss of bone that can commence early in life. Although there is much focus on diagnosing the disease in individuals aged over 50, the detection and prevention of impaired bone health in younger adults receives less attention.
The possibility of impaired bone health should be considered in patients of all ages. Certain diseases and drugs are associated with increased risk, but modifiable lifestyle risks are often overlooked. Smoking, alcohol, dietary avoidances, eating disorders and inactivity are common risks.
Lightweight, lean endurance athletes and dancers with low energy intake - male and female - are also at risk because of complex effects on hypothalamic inhibition and hypogonadism. Any form of menstrual dysfunction can have negative effects on bone.
The most common approach to assessing bone quality is measurement of bone density, which correlates with bone strength. DXA is the tool of choice in assessing bone density.
Bone mineral density (BMD) measurement is not routinely indicated in healthy young men or premenopausal women. However, it should be considered in those where there is a concern because of their clinical risk factor profile - patients with secondary causes of impaired bone health and those who sustain a fragility fracture.
BMD assessment with bone health education can have a significant effect on behaviour that affects bone health, such as smoking, alcohol intake, nutrition and exercise.
HRT significantly reduces bone loss in women with amenorrhoea/oligomenorrhoea, those with endometriosis on gonadotropin-releasing hormone agonist therapy and those with perimenopausal bone loss.
The decision to use bone agents, including bisphosphonates, parathyroid hormone and others, is on a case-by-case basis and the patient should be under specialist care. Shortand long-term effects on younger people and on the fetus are still not entirely clear and all agents must be used with great caution.
Bisphosphonates or teriparatide (in those with fused epiphyses) are options for individuals on glucocorticoids ≥7.5mg daily for three months or more who have sustained a fragility fracture or show accelerated bone loss (≥4% per year) or others (for example, those with multiple risks). Again, specialist input is indicated.
All patients should be reviewed in relation to lifestyle, disease control (where appropriate) and medications. Patients who have demonstrated reduced bone mass should have follow-up DXA in one to two years. Those on glucocorticoids should have annual DXA.
- Professor Speed is consultant in rheumatology sport & exercise medicine at The Fortius Clinic, London, and the Cambridge Centre for Health & Performance