Calcium, physical activity and bone health ± building bones for a stronger future Francesco Branca* and Silvia Vatuen Äa Istituto Nazionale per gli Alimenti e la Nutrizione, Via Adreatina 546, Rome, Italy Abstract Adequate provision of nutrients composing the bone matrix and regulating bone metabolism should be provided from birth in order to achieve maximal bone mass, compatible with individual genetic background, and to prevent osteoporosis later in life. Low calcium intake (,250 mg day 21 ) in children is associated with both a reduced bone mineral content and hyperparathyroidism. Optimal calcium intake is, however, still a matter of controversy. The minimisation of fracture risk would be the ideal functional outcome on which to evaluate lifetime calcium intakes, but proxy indicators, such as bone mass measurements or maximal calcium retention, are used instead. Calcium recommendations in Europe and the United States are based on different concepts as to requirements, leading to somewhat different interpretations of dietary adequacy. Minerals and trace elements other than calcium are involved in skeletal growth, some of them as matrix constituents, such as magnesium and fluoride, others as components of enzymatic systems involved in matrix turnover, such as zinc, copper and manganese. Vitamins also play a role in calcium metabolism (e.g. vitamin D) or as co-factors of key enzymes for skeletal metabolism (e.g. vitamins C and K). Physical activity has different effects on bone depending on its intensity, frequency, duration and the age at which it is started. The anabolic effect on bone is greater in adolescence and as a result of weight-bearing exercise. Adequate intakes of calcium appear necessary for exercise to have its bone stimulating action. Keywords Mineral requirements Bone growth Osteoporosis Children Adolescents Introduction Osteoporosis, a disease affecting several million people in the world, should be prevented from childhood by achieving maximal bone mass compatible with individual genetic background. It is even possible that prevention should start as early as during pregnancy, since maternal health and nutrition affects in utero bone growth and development 1 . Bone mass increases until the third decade of life, then slowly decreases. In women, 15% of the peak bone mass will be lost in the first 5 years after menopause 2 and up to 30±50% before the age of 70 3 , when menopause-related bone loss is concluded. The bone loss rate associated with the process of ageing is approximately 1% per year in men and women 4 . Therefore, having a larger bone capital and spending it more parsimoniously, i.e. reducing bone loss, delays the attainment of a bone density level at which fracture risk is high. Fracture incidence in individuals whose bone density is greater than 1 SD above the mean is 50% lower at 80 years 4 . Peak bone mass is determined by the genetic back- ground of the individual and by a combination of environmental influences that can explain up to 40% of the variance in bone mass, including usual body weight, weight-bearing physical activity and intake of certain nutrients known to compose the bone matrix or regulate its metabolism 5 . This review intends to summarise the role of calcium, other minerals and vitamins and physical activity in the achievement of the maximal peak bone mass allowed by a given genetic potential. Calcium Since approximately 70% of the bone weight is accounted for by calcium phosphate crystals, it is obvious to think of calcium as the first nutrient to be required for optimal bone growth. Very low calcium intake in children induces rickets, osteomalacia and growth retardation. Infants having intakes below 200 mg day 21 have radiographic appearance of rickets and 5-year-old Chinese children consuming less than 250 mg day 21 of calcium had DOI: 10.1079/PHN2000105 Public Health Nutrition: 4(1A), 117±123 *Corresponding author: Email f.branca@agora.it q The Authors 2001