Last updated by Dr Sarah Brewer on
Calcium supplements are widely prescribed to both prevent and treat osteoporosis and to reduce the risk of bone fractures. As well strengthening bones, calcium is vital for energy production in cells, for nerve conduction and muscle contraction – including a regular heartbeat.
In fact, calcium is so important for your health that blood levels are tightly controlled. If your blood level falls too low as a result of poor dietary intakes, it gets topped up by leaching calcium directly from your bones. That’s why long-term lack of calcium increases your risk of a bone fracture.
Calcium can only work properly if sufficient vitamin D is present to regulate its absorption from the gut and its deposition in bone. If your vitamin D status is low, then no matter how much calcium is present in your diet, you simply won’t absorb it.
Negative calcium reports
A recent publication in the British Medical Journal attracted a rash of negative headlines as it appeared to suggest that increasing your calcium intake is unlikely to reduce your risk of bone fractures. But before you throw away your calcium supplements, it’s important to look at what the researchers actually found.
This meta-analysis looked at all the results from a total of 72 studies. Of these, only two were gold-standard, randomised controlled trials of dietary sources of calcium. Another 44 studies explored associations between self-reported dietary intakes of calcium, milk or dairy, and fracture occurrences. The remaining 26 studies were the most important – these randomised controlled trials actually looked at the effects of taking calcium supplements one bone fracture risk.
The 44 studies looking at dietary calcium alone (eg from milk and dairy) found no significant link between calcium and fractures. But the majority of these studies did not take vitamin D status into account, so it’s difficult to draw any meaningful conclusions from them.
Another factor is that the bioavailability of calcium from vegetable in the brassica (cabbage family) is almost twice as high as the calcium within dairy products. As much as 61% of the calcium in broccoli is absorbed, for example, compared with only 32% of that in milk, for example, although the reason is poorly understood.
Some types of dietary fibre (phytates from wheat in unleavened bread such as chapatti) also bind calcium in the bowel to form an insoluble, non-absorbable salt, and these associations were not explored in the studies. Similarly, high-fibre diets, which speed the passage of food through the bowels, will reduce the amount of calcium absorbed. All these factors mean that trying to find a link between dietary calcium intakes and subsequent risk of bone fractures is not as simple as it sounds.
Calcium supplements protect against osteoporosis
The studies that looked at calcium supplements DID find a significant protective effect on bone, but this was rather lost in newspaper reports. A large analysis of data from 26 studies, involving over 58,500 people, found that taking a calcium supplement reduced the risk of any bone fractures by 11%, and of vertebral fracture by 14%.
A trial involving elderly women living in residential care, and who had both a low dietary calcium intake and a low vitamin D status, found that taking calcium plus vitamin D supplements reduced their risk of hip fracture by as much as 23%.
So, if you have osteoporosis or are at risk due to family history or other factors, please ignore the recent headlines. If your doctor has advised you to take calcium supplements, please continue to take them. Given that vitamin D deficiency is so widespread, combining calcium with vitamin D is important for optimum absorption and bone benefits.
Supplements often include magnesium for its beneficial effects on bone strength.
Vitamin K2 is also important when taking calcium supplements to help regulate its removal from soft tissues, and to prevent calcification of the arteries. Not all supplements include these, however, so check labels to make sure you are getting the most effective formulation.
What’s the best dose?
Previous studies suggest that the most effective combination is 1200 mg calcium plus 20 mcg (800 IU) vitamin D3.
Click here to read how diet can help to prevent osteoporosis.
Do you take calcium supplements to help prevent or treat osteoporosis?
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