It is already known that calcium along with vitamin D are important in keeping bones healthy. In the US, the guideline for calcium intake was 1000 mg a day for women under the age of 50, 1200 mg for older women with the upper intake level of 2000 mg because of kidney stones and other risks caused by high calcium intake. In the UK, the recommended Ca intake for adults is 700 mg a day.
Several recent studies linked calcium supplements to increased risk for cardiovascular events and kidney stones in women. A new study published in the BMJ looked at the relationship between calcium and risk for fractures and overall bone health involving more than 61,000 Swedish women, followed up for 19 years.
The study found that women with the lowest Ca intake, below 750 mg, had a higher risk of fractures or develoing osteoporosis, but increasing intake of Ca did not reduce the risk of fracture further. Women who had the highest Ca, 1100+ mg seemed more at risk of broken hip. It concluded that moderate levels of calcium intake were best for bone health and more was not better.
The large size of the study with better precision is regarded a strength of the study, but critics say researchers used a questionnaire covering diet and lifestyle to find out how much calcium women were getting from food may result in recall bias. Experts suggest women should get enough calcium from a balanced diet, eg half pint of milk, green vegetables and nuts.
Source: "Dietary calcium intake and risk of fracture and osteoporosis: prospective longitudinal cohort study". BMJ 2011; 342:d1473 (Published 24 May 2011) Open access
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