Calcium is essential to our survival, 99% of the body's calcium is in the skeleton where it complexed with other minerals it forms hard crystals giving bones their strength. That strength is essential for our ability to grown, maintain posture, protect our organs and, by being the secure anchor for the muscles to insert into, essential to locomotion, work and even breathing. The small proportion of calcium that is not in the bones is needed for every nervous impulse and muscle contraction and even as a cofactor for the innumerable chemical reactions on which we depend.
We take calcium in the diet and its absorption is dependent on active vitamin D (1, 25 hydroxy cholecalciferol). If the body needs calcium it will mobile it immediately from the skeleton under the influence of parathyroid hormone (PTH). The calcium in the skeleton is constantly released and taken back into the bone in response to skeletal load (this remodelling is how bones recover from fractures, grown and get stronger in response to mechanical need. The bones grow stronger until their peak mass is achieved, roughly around the age of 25 years of age, and from then on they get weaker. In women the loss of oestrogen (and ovarian androgens [male hormones]) at the menopuase suddenly changes the balance within the skeleton and they thin more quickly. There is not this sudden loss of sex hormones (particularly the androgen testosterone, which is in fact changed in fat cells - aromatised - to oestogen in men, so there is not an abrupt change in bone density. Women also achieve a lower peak bone mass in young adulthood. For these two reasons women are more prone to bone thinning or reduced bone density as they age, this might become osteopaenia or if thinner still osteoporosis.
Osteopaenia and osteoporosis are important measures of bone density and strength as the thinner, or less dense, the bones are the less able they are to do their job, they may fracture when they normally would not; this is an important problem at the hip and wrist if we fall and also in the spine. If there are multiple fractures in the spine one will loose height and excessive curvature of the thoracic spine (kyphosis) can occur.
For general health, but in this context, bone and skeletal health it is necessary to maintain an adequate dietary calcium intake, and also necessary to have adequate vitamin D. Most of our vitamin D is in a storage form - 25 hydroxy cholecalciferol, and it can be converted as necessary (under the influence of PTH) in the kidneys to active vitamin D. To have adequate vitamin D stores we have to make it in the skin or take it in the diet, only then could we absorb calcium if it were in the diet.
The amount of calcium we need in the diet throughout life does change a little but broadly it is 1000 mg, and 1200 mg when we are older and if we do not take this in the diet the bones will provide the calcium and become weaker. There is a very helpful calculator at the International Osteoporosis Federation website to help calculate how much calcium is in the diet; this can either help change the diet to include more calcium or take calcium supplements. Dairy produce is a very common source of calcium for many people and the calculator is useful for vegans or those who do not take dairy produce to know how they might maintain their intake.
Osteopaenia and osteoporosis are very common. The latter can be diagnosed if a patient has a fracture at a characteristic site with an inadequate explanation, for example a fall onto an outstretched hand should not fracture the wrist, a fall onto the side from standing height should not fracture the hip and the spinal vertebrae should not fracture. Osteopaenia and osteoporosis can also be diagnosed by assessing bone density with dual energy X ray absorbtiometry (DEXA) using a very low dose of radiation. There are other important tests used for special situations such as vertebral fracture assessment, urine bone turnover markers and CT of the bones (to correct an important failing in DEXA when the bones are small).
If you would like to consider your own bone health consult a doctor with an interest in osteoporosis. Dr Philip Kelly is an endocrinologist, metabolic and general physician working at King's College Hospital with an interest in maintaining bone health, preventing osteopaenia and osteoporosis and treating it if it has occurred. This includes keeping calcium balance, advising on the pros and cons of calcium tablets and ways to ensure your vitamin D is sufficient. For an appointment the Guthrie Clinic can be contacted by telephone on 020 3299 3848 or email here.