[The role of calcium at different ages in women's life]

The present long life of women raises the problem of prevention against osteoporosis. Bone mass formation during adolescence is the first critical period, and it might condition the future bone mineral content. Eighty percent of the bone mass is of genetic origin, whereas 20 percent depends on the environment (diet, hormones, etc.). Menstrual disorders may be responsible for bone mineral loss. Pregnancy and breast-feeding are periods in which calcium requirements increase, yet in all but high risk women there are seldom responsible for osteopoenia. The first 10 years of menopause constitute a period of exponential bone mineral loss, and this is when oestrogen therapy is most effective against bone loss. The usefulness of calcium is still a matter of debate, with conflicting results concerning its preventive action on osteoporosis. There seems to be a threshold phenomenon: when normal diet provides a small amount of calcium, calcium supplementation is effective, but beyond a certain level supplementation is thought to be useless. The results found in the literature are presented, and the amounts of calcium intakes recommended at different ages are given.