Studies linking calcium intakes to heart concerns continue to be published, but studies showing no effects and even benefits can also be found in the literature, so what are the lessons to learn and what questions remain unanswered?
Osteoporosis has been described as a silent killer, and recent data from the National Osteoporosis Foundation showed that approximately 9 million American adults currently have osteoporosis and another 48 million have low bone mass, placing them at increased risk.
An economic report from Frost & Sullivan and commissioned by the Council for Responsible Nutrition (CRN) recently found that supplements of calcium plus vitamin D for all US women with osteoporosis could provide healthcare cost savings of $1.08 billion per year.
Despite the clear benefits of calcium (and vitamin D) for bone health, papers published in journals such as JAMA , Heart , and the British Medical Journal found significant adverse cardiovascular effects related to excessive calcium intake in different populations, leading to concerns, and even condemnation of calcium supplements by some. (The plaques that form in diseased arteries are composed mostly of calcium.)
The literature, however, is contradictory, and even the anti-calcium articles do not always support each other: The JAMA article, for example, found an increased heart disease risk in men, but not women, while the BMJ study reported detrimental effects in women.
On the flip side, a report from the Institute of Medicine concluded that “evidence from clinical trials currently does not support an effect of calcium intake on risk of cardiovascular disease”.
In addition, Harvard Medical School researchers reported in November 2012 no link between calcium supplements and an increased risk of artery calcification, according to analysis of data from the Framingham Offspring Study published in the American Journal of Clinical Nutrition .
Results of a new long-term calcium supplementation trial from China published in the most recent issue of the American Journal of Clinical Nutrition are sure to muddy the waters further. Scientists from the Harbin Medical University report that two years of supplementation with 800 mg of elemental calcium as calcium carbonate increased cholesterol levels and carotid intima-media thickness (a marker for atherosclerosis) in postmenopausal women with irregular blood lipid levels (dyslipidemia).
Interestingly, a “significant interaction between calcium supplementation and menopausal status” was revealed by the study, with no adverse effects being observed in pre-menopausal women with dyslipidemia.
Commenting on the findings, Duffy MacKay, N.D., vice president, scientific and regulatory affairs at the CRN, told us that the lack of finding in pre-menopausal women means there should be no change in behavior for them to build bone strength. “For pre-menopausal women it is critical to establish the bone density,” he said.
A recent review published in Nutrients (2013, Vol. 5, pp. 3964-3974) by John Anderson and Philip Klemmer from the University of North Carolina stated that: “Many patients do not understand that the critical time for optimal calcium intake occurs during the formative bone growth years and incorrectly assume that high calcium intakes in late life promote an increase in BMD and thereby reduce their bone fracture risk.
“With respect to the effect of optimal calcium intake, the window of opportunity to build strong bones closes by approximately the beginning of the third decade of life.
“The maintenance of BMD and bone health continues to be an important goal of adequate dietary calcium consumption, but eliminating potential risks of CVDs from excessive calcium intakes needs to be factored into policy recommendations for calcium by adults,” added Anderson and Klemmer.
Later in life
So what is it about post-menopausal women? This population group has been described as “unique” because of the hormonal changes that occur.
For the post-menopausal women, Dr MacKay said that the research community is only beginning to scratch the surface with estrogen and bone density. “It’s exciting in the sense that nutrients and hormones work together. We need to understand how this is related to estrogen.”
Another new review paper, this time by scientists from Cardiff University and the University Hospital of Wales in the UK, said that the data in the literature relating to post-menopausal women is, “contradictory and controversial, however, overall it suggests that high calcium levels, whether through natural diet or supplementation, may lead to increased risk of cardiovascular events despite potentially positive benefits in multiple risk factors such as plasma HDL and LDL levels, and HDL/LDL ratio, as well as reductions in blood pressure.” (Atherosclerosis , Nov 2013, Vol. 231, pp. 1-7)
Noting that, as populations age, the number of post-menopausal women is “increasing rapidly”, the Wales-based scientists said that this population group should “be studied exclusively and more extensively”.
‘Not for everyone’
Following publication of the JAMA study from February 2013, Susanna Larsson, PhD, from the Karolinska Institutet in Sweden commented that the available data are "suggestive of adverse cardiovascular effects with an excessive intake of supplemental calcium.
“The paradigm ‘the more the better’ is invalid for calcium supplementation,” she added.
General consumer advice has remained very balanced on the subject, with the message being to adhere to the recommendations. The Mayo Clinic website , for example, states: “Calcium supplements aren't for everyone.
“If you take calcium supplements and eat calcium-fortified foods, you may be getting more calcium than you realize. Check food and supplement labels to monitor how much calcium you're getting a day and whether you're achieving the RDA but not exceeding the recommended upper limit.”
“Most nutrition savvy dieticians would not give calcium in isolation”
Questions have also been raised about the focus exclusively on calcium and the formulation of bone health products in general. “This is an obvious strong talking point,” said Dr MacKay. “Most nutrition savvy dieticians would not recommend calcium in isolation. It’s about calcium plus vitamins D and other nutrients.”
One such other nutrient is vitamin K: Results from the Rotterdam Study in the Netherlands, published in 2004 in The Journal of Nutrition (Vol. 134, pp. 3100-3105), concluded that the highest average intakes of vitamin K2 (menaquinone) were associated with a 52% reduction in the risk of ‘severe aortic calcification’.
Despite this being reported nine years ago, and being supported in the scientific literature (and promoted by vitamin K2 suppliers) over the years, many bone health products – and multivitamins – remain devoid of vitamin K.
Eric Anderson, Sr. VP Global Sales & Marketing for vitamin K2 supplier NattoPharma, calls vitamin K2 the “forgotten vitamin”.
“Irrefutable evidence shows that vitamin K2 helps preserve bone mass and strength, and inhibits and even regresses calcium accumulation in the arterial walls. Vitamin K2 helps put calcium in its place,” he said.
“The best source of K2 in the Western diet is fermented cheese. But with American processed singles and Mac & Chemicals, which is not cheese, my concern is that our population, and especially our children, is systematically deprived of this essential vitamin."
For NattoPharma’s head of R&D, Vladimir Badmaev, MD, PhD, the solution is simple: “Calcium and vitamin D supplements should not be avoided, but complemented with vitamin K2 supplementation due to its increasingly recognized role as a calcium chaperone and the facilitator of K’s cardiovascular system protective role in the body,” he said.
“This emerging trend in vitamin K’s (K2 in particular) supplemental use has been further supported by the most recent clinical study [in the AJCN] and the new clinical methods evaluating deposits of calcium in the arteries.”