Ingesting foods high in calcium will not help if those sources of calcium are not well absorbed. A supplement may help. The many supplements available today get their calcium from a number of different sources. One of the most popular sources is coral calcium. Coral calcium exists in the form of calcium carbonate and is often readily available in pharmacies or health food stores.
Calcium supplements are not easily absorbed in the intestine, and it is estimated that the maximum dose that can be absorbed at one time is 500 mg. This means that for daily doses greater than 500 mg/day, such as those needed by perimenopausal women (women in the beginning stages of menopause) or those at risk for osteoporosis, pill taking should be spaced out throughout the day.
Another thing to consider is that sufficient stomach acid is required for adequate calcium absorption. Therefore, supplements should be taken towards the end of a meal when the pH of the stomach is optimal.
Vitamin deficiencies can contribute to decreased calcium absorption. In particular, vitamin D plays an important role in calcium uptake and metabolism, and, as a result, deficiencies in vitamin D are associated with bone loss and bone fractures.
Normally, the kidney activates vitamin D from a precursor synthesized in the skin in a reaction involving sunlight. Reduced exposure to the sun can inadvertently contribute to deficiencies in the vitamin, with subsequent bone damage. Such conditions have been described, and are referred to as rickets when observed in children, and osteomalacia when observed in adults. When the cause of the deficiency is a poorly functioning kidney, the associated bone weakening is referred to as renal osteodystrophy.
The National Academy of Sciences recommends 200-400 international units (IU) per day of vitamin D. Women over seventy should take up to 600 IU. One good source of vitamin D is milk, which is often fortified with both vitamins D and A.
Other vitamins that may aid in preventing osteoporosis are vitamins E and C. Both of these have antioxidant properties and may be particularly beneficial in high-risk groups like smokers. Smoking is a known risk factor in the development of osteoporosis, and smokers deficient in vitamins E and C appear to be at an even greater risk.