Women who get most of their daily calcium from dietary sources have healthier bones than women whose calcium comes mainly from supplements, says new research.
"Only about 35 per cent of the calcium in most supplements ends up being absorbed by the body" said Armamento-Villareal.
"Calcium from the diet is generally better absorbed, and this could be another reason that women who got a high percentage of calcium in their food had higher bone densities."
The study, published in the American Journal of Clinical Nutrition, followed 168 healthy postmenopausal white women and reports that the benefits of dietary sources even held true when supplement takers have higher average calcium intake.
The use of calcium supplements is widely accepted by the general public, with the mineral reported to be the biggest seller in the US supplements industry, with annual sales of about $993 (Euros 836) million in 2004, according to the Nutrition Business Journal.
The new study, led by Reina Armamento-Villareal, from Barnes-Jewish Hospital, has implications for the supplements industry with the researchers indicating that consumers may not be aware that calcium carbonate, for example, should be taken with meals to improve calcium absorption. Calcium citrate tablets don't have this limitation.
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The researchers evaluated the average total daily calcium intake from dietary and supplemental sources of the postmenopausal women. Measures of oestrogen metabolites in the urine, and spine and proximal femur bone mineral density (BMD) were also taken.
The women were divided into three groups: the "supplement group," got at least 70 per cent of their daily calcium from tablets or pills (average 1,030 mg/d); the "diet group," got at least 70 per cent of their calcium from dairy products and other foods (average 830 mg/d); and the "diet plus supplement group," obtained calcium from both sources in between these ranges (average 1,620 mg/d).
Despite having the lowest calcium intakes, the women in the "diet group" were found to have higher bone density in their spines and hip-bones than women in the "supplement group". Women in the "diet plus supplement group" had the highest bone mineral density.
When the researchers looked at levels of the oestrogenic metabolites, they found that women with dietary sources or mixed sources of calcium had higher rations of the active metabolite (1/16-hydroxyestrone) to the inactive (2-hydroxyestrone) than women who received most of their calcium from supplemental sources.
"Calcium from dietary sources is associated with a shift in oestrogen metabolism toward the active 16-hydroxyl metabolic pathway and with greater BMD and thus may produce more favourable effects in bone health in postmenopausal women than will calcium from supplements," concluded the researchers.
The study was funded by the National Institutes of Health and the General Clinical Research Centre at Washington University. Osteoporosis is estimated to affect about 75m people in Europe, the USA and Japan. According to the International Osteoporosis Foundation, the total direct cost of osteoporotic fractures is €31.7bn in Europe and 17.5bn in the US (2002 figure). The total annual cost of osteoporosis in the UK alone is over £1.7bn (€2.5bn), equivalent to £5m (€7.3m) each day!
Source: American Journal of Clinical Nutrition Volume 85, Pages 1428-1433
"Effects of dietary calcium compared with calcium supplements on estrogen metabolism and bone mineral density" Authors: N. Napoli, J. Thompson, R. Civitelli, R.C. Armamento-Villareal