Osteoporosis is a progressive reduction of bone density, which makes the skeleton gradually ever more brittle. Although we know the many risk factors a small frame, an early menopause, or the use of certain drugs (tetracycline, excess thyroxine, lon
In osteoporosis there are often low levels of calcium absorbed, largely because of intestinal malabsortion. This may be due to inadequate levels of vitamin D3, which is synthesized into calcitriol, an important regulator of calcium absorption and stimulant of bone production, which itself is closely regulated by circulating levels of parathyroid hormone (PTH), by phosphate and concentrations of calcium in the serum (Calc Tissue Res, 1991; 49: 4 suppl 1: S46-S49; Metabolism, 1990; 39(4 suppl): 3-9).
Vitamin D3 is actually a hormone, not a vitamin. Like cortisone or
progesterone, it and calcitriol are formed from a cholesterol like substance in the skin by ultraviolet rays in sunlight. It markedly increases the percentage of calcium taken up into the bloodstream from the diet through the gut lining and stops most of the calcium and magnesium we consume from being lost in the urine, so recycling much of these minerals back into the bloodstream. It also ensures that more calcium enters the bones and stays there (J Mineral Electr Metab, 1984; 10: 375-8).
In the elderly, the problem occurs because of a lack of exposure to sunlight, and the decreasing ability of aging skin to synthesize vitamin D (J Engl J Med, 1981; 305: 372-4). Chronic dietary vitamin D deficiency is also common in this age group, as is a waning ability for the kidneys to synthesize calcitriol. Aging also reduces the number of calcitriol receptors both in the intestine and in the bone (Endocrinology, 1990; 126: 1053-7). And of course 50 per cent of the elderly have low stomach acid, which seriously impairs calcium absorption from the digestive tract (Am Geriatric Soc, 1967; 15: 786).
For sunlight and vitamin D to be successful in helping prevent osteoporosis, by stimulating bone remodelling and keeping levels of PTH normal, it's important that you have proper digestive function and adequate supply of dietary calcium.
Despite the universal Western belief that without milk it's impossible to get enough calcium, cow's milk products also contain a level of phosphorus high enough to interfere with calcium uptake (D Downing. Day Light Robbery: The Importance of Sunlight to Health: Arrow Books Ltd, London, 1988). Furthermore, many non-dairy foods have very high levels of calcium. If you compare 100 g of various foods, almonds contain 250 mg calcium, tofu contains 507 mg, dried figs contain 280 mg and red kidney beans 140 mg.
For people 50 years and older, living in latitudes with limited exposure to sunlight, the recommended intake for vitamin D3 is 200 IUs a day. (Rapport due Comite de Revision Scientifique De 1900, Ottawa: Approvisionnement et Services Canada 1900: No H-49-42/1990E). This intake is just barely adequate to prevent seasonal fluctuations in calcitriol and PTH in healthy white post-menopausal women in such areas (N Engl J Med, 1989; 321: 1777-83). One study showed that a daily intake of 400 IUs during one year by these women significantly reduced late winter-time bone loss and increased their net spinal bone density (Ann Internal Med, 1991; 115: 505-12).
Harald Gaier is a registered naturopath, homeopath and osteopath.