Title: Calcium and Bone Health

Key words: Bone skeleton, osteoporosis, calciferol, Vitamin D, Magnesium

Date: Aug 1999

Category: 11. Life Changes

Type: Article

Author: Dr van Rhijn

 

Calcium and Bone Health

Implications for older people.

 

Introduction

Several micronutrients are involved in the maintenance of bone (a highly complex mineralised matrix). Demineralisation (osteoporosis) is a major health problem among the elderly.

Calcium and Vitamin D

Calcium, the major mineral constituent (1kg) of the skeleton1 is controlled by numerous hormones and interactions with other nutrients. Deficiency (numerous causes) leads to osteoporosis (bone volume reduction). Calciferol (1,25(OH)2 D3), a metabolic product of vitamin D, promotes the absorption of calcium. Reduced vitamin D levels (e.g. in winter2), result in diminished absorption, an increase in parathyroid hormone secretion and calcium mobilisation from bone and osteomalacia. A significant number of the elderly, (those in institutions, the housebound and Asians) have a low vitamin D status3. Absorption of calcium and, possibly, of vitamin D decline with age.

Other Nutrients

Magnesium and phosphorus are closely associated with calcium absorption, metabolism and bone density. Approximately 65% of the total body magnesium4 and 80% of the total body phosphorus is present in bone, and deficiency is associated with osteomalacia. Other elements such as boron, fluoride, manganese, copper, lithium, molybdenum, silicon and vanadium are concentrated in bone and any deficiency contributes to osteoporosis, although their precise role is still unknown. Increased salt intake (10 fold in western diets [150 200 mmol/day]), causes increased extracellular volume (1 2 L5) and an increase in calcium, hydroxyproline and parathyroid hormone excretion. Calcium loss6, not compensated for by increased absorption, will result in bone demineralisation, especially in the hypertensive elderly. Salt restriction promotes bone mineralisation7 and reduces the frequency of hip fractures. Vitamin K may be involved in bone mineral loss (osteocalcin activation), skeletal fragility and osteoporosis, although its exact role is still unclear8.

Excess of micronutrients also lead to bone disease: vitamin D (hypercalcaemia and calcification), vitamin A (ligament ossification), aluminium (osteodystrophy), boron (osteoporosis) and fluoride (hyperostosis and ligament calcification),

Implications for the Elderly

The increased demineralisation9 from the age of 30-40 years is accelerated after menopause10 and results in osteoporosis and increased risk of fractures11. Peak bone mass quality determines the amount of bone present in adulthood. There are an estimated 60,000 hip, 50,000 wrist and a further 40,000 vertebral fractures annually in the UK, and the actual number is likely to be higher12. The relationship between bone mineral content (osteoporosis) and incidence of fracture is strong13, resulting in significant mortality, morbidity and economic cost14.

Supplementation & Recommendations

Exposure to sunlight and fortified foods provides the majority of the required vitamin D. Dietary calcium intake, from dairy products and cereals should be encouraged. Current COMA recommendations for the elderly are a RNI of 10 m g/day for Vitamin D and 700 mg/day for calcium15. These figures fall short of the recommended intakes of 1500 mg/day set by the NIS of the USA16. Randomised controlled trials confirmed that supplementation with calcium17, 18 (with other minerals19) and vitamin D20 reduces bone loss in the elderly and reduces the risk of fractures21.

Conclusion

The COMA Subgroup on Nutrition and Bone Health recommends a healthy lifestyle, with a varied, adequate diet and regular weight-bearing activity to maintain bone health.

 

References

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