Calcium confusion: scientists divided over supplements
A clash between supporters and detractors of calcium supplements for better bone health is leading to conflicting headlines, leaving the public unsure about whom to believe. Osteoporosis is estimated to cost the Australian economy more than $7 billion a year. It’s a condition that affects around 700…
A clash between supporters and detractors of calcium supplements for better bone health is leading to conflicting headlines, leaving the public unsure about whom to believe.
Osteoporosis is estimated to cost the Australian economy more than $7 billion a year. It’s a condition that affects around 700,000 Australians, the vast majority of whom are women. In 2009-10, nearly 7,000 Australians were hospitalised as a result of osteoporosis.
It’s accepted that limited exposure to sunlight resulting in low vitamin D intake is a risk factor contributing to osteoporosis, and the National Health and Medical Research Council (NHMRC) says the combination of calcium and vitamin D can help reduce the chance of breaking bones.
But scientists differ on where people should get their calcium.
Last month, independent health experts from the US Preventive Services Task Force said adding vitamin D and calcium to a healthy diet does not lower risk of fractures in post-menopausal women, and that for younger women and men, the studies were too inconclusive to support regular use of supplements.
This is despite a Women’s Health Initiative study on the benefits and risks of daily calcium and low-dose vitamin D supplements finding they led to a 12% reduction in hip fractures for women aged 50-79, and a 21% reduction for women aged over 60. Those women with intakes above 1200 mg per day did not clearly get additional benefit from the intervention, suggesting that more is not necessarily better.
It’s clear that sufficient calcium is good for bone health, but at the heart of the recent debate over supplements are new studies linking calcium supplements with heart disease.
It’s a body of research that Professor Christopher Nordin, who has been working in the area of calcium metabolism and osteoporosis for more than 50 years, strongly refutes.
He says the evidence of benefit from calcium and vitamin D supplements is very well established, particularly for post-menopausal women, and points out that the Women’s Health Initiative study of post-menopausal women found no association between calcium supplements and heart attacks.
“The absorption of calcium goes down at the menopause and the urinary calcium goes up, so the requirement for calcium goes up,” Professor Nordin said.
Last month a group of doctors called for more scrutiny to be placed on the marketers of supplements, after the journal Advances in Nutrition published an article that was funded by a supplements trade association.
In a letter to the editor published in the BMJ, Dr Ian Reid and colleagues from the University of Auckland said two of the six authors of the paper published by Advances in Nutrition are employees of the Council for Responsible Nutrition, a trade association representing dietary supplement manufacturers.
The paper in question, by Dr R.P. Heaney of Creighton University’s Osteoporosis Research Centre, argued the evidence presented to date on the relationship between calcium supplement use and increased cardiovascular disease risk was not sufficient to warrant a change in the Institute of Medicine recommendations, which advocates the use of supplements to promote bone health in people who do not get the recommended intake of calcium through their diet.
Dr Reid said it was a concern that the literature was being influenced by groups, such as CRN.
While the support of the CRN for the study in question was disclosed in the Advances in Nutrition article, Dr Reid said it was part of larger and carefully coordinated press campaign to promote a view that was commercially advantageous to the CRN and its members.
“The thing that struck about it was the blatancy with which it was done, and that really contrasts dramatically with what happens in the pharmaceutical arena. Most academics go to great strains not to be seen to be captured by any lobby group,” Dr Reid said.
However, Professor Nordin said there was very little profit and negligible industrial contribution from calcium and vitamin D supplements.
He went further and argued Dr Reid had no right to criticise Dr Heaney because he had in the past received funding support from Fonterra, a New Zealand multinational owned by dairy farmers.
Dr Reid said he had not received any funding from the dairy industry in the last three years and none of his calcium studies had been funded by them.
A paper by Dr Reid published in the BMJ in 2010 disclosed that he had previously received research support from, and acted as a consultant for, Fonterra.
Professor Nordin said he once received a grant from Roche who manufacture a form of vitamin D called calcitriol, and 60 years ago he received a travel grant from Sandoz who used to market a calcium preparation.
Journals and responsibility
Dr Reid argues academic journals need to be very aware of potential conflicts of interest, and is concerned there may be a double standard when it comes to supplements.
“I’m not confident in the supplements space generally that the levels of scrutiny are what we would expect in other areas such as the pharmaceuticals area,” he said.
However, physician and health ethicist Paul Komesaroff said as long as the partisan nature of the argument was openly stated, there was nothing wrong with scientists arguing the case for the manufacturers of calcium supplementation.
“Whether Heaney is employed by the drug industry or not does not invalidate his argument,” Professor Komesaroff said.
“In a court of law we are comfortable to accept the role of an advocate for a particular point of view – with the provision that the allegiance of the advocate is openly stated – and I can see no reason why we should not be equally happy with such a system in science.”
Professor Komesaroff added that despite claims to the contrary, no scientific argument is free from interests of some kind or other.
“Scientists like to think of themselves as radically sceptical, but this is far from the case. Indeed, it is well recognised that scientists become very attached to their own points of view and tend to resist change, even in the face of strongly contrary evidence.”
However, Dr Reid said there were other ways for supplement manufacturers to reach the market.
“If something is dressed up as an objective review and published in an academic journal then that is a less acceptable way for supplement manufacturers to express their point of view,” Dr Reid said.
The publisher and editor of Advances in Nutrition did not respond to our request for comment.
Natural is best
The NHMRC recommends adults have a daily intake of calcium of 1,000 milligrams per day, and this rises for women aged over 50 to 1,300 milligrams per day to account for increased need at menopause. It recommends an upper limit of 2,500 milligrams per day, with the rationale that adding 1,000 mg of calcium to a typical western diet would only increase calcium in urine by about 60 mg.
Vitamin D, made in the body by the action of sunlight on the skin, is also critically important, because it helps the body to absorb calcium.
The guidelines are similar in the United States, however the US Preventative Services Task Force says more evidence is required to “assess the balance of the benefits and harms of daily supplementation with greater than 400 International Units of vitamin D and greater than 1,000 mg of calcium for the primary prevention of fractures in non-institutionalised postmenopausal women”.
Based on the available evidence, the strongest argument is that people should try to get their daily intake of calcium and vitamin D by eating a diet rich in these nutrients. For postmenopausal women, the benefits of supplements appear to outweigh the risks. With more research, the case for and against supplements is expected to become clearer.