The Link Between Supplemental Calcium and Cardiovascular Disease
The latest study looked at long-term health in a large group of Swedish women, assessing their calcium intake and cardiovascular mortality (death connected to heart problems). What they found was that high calcium intakes were associated with increased likelihood of death from all causes (including cardiovascular disease), but that such high intakes were not significantly associated with mortality from strokes.
Heart Disease and Calcium Intake
Publishing their research in the British Medical Journal this month, Karl Michaëlsson, MD, PhD, professor in medical epidemiology and senior consultant in orthopedic surgery at Uppsala University in Sweden, and colleagues are the latest to add to research connecting CVD and calcium intake. Many of these studies are actually finding that calcium supplements are the likely problem, not necessarily high dietary calcium, although media reporting has been somewhat lax on that distinction.
Too Much Calcium?
Why might calcium supplements be dangerous? Is it possible to have too much of a good thing when it comes to nutrition? Just as too much vitamin A can be toxic and have detrimental effects, and even too much vitamin C can cause digestive problems and diarrhoea, calcium may also be problematic at high doses. The difference between diets high in calcium and dietary calcium supplements is that dietary calcium is usually tied to other nutrients, including magnesium, phosphorus, and even vitamin D in some foods. Stripping these nutrients away and simply supplementing with calcium means that the body struggles to use the mineral appropriately. Vitamin D and magnesium are essential for calcium to be properly absorbed and used in bone-building. Even vitamin C is arguably necessary to help with calcium metabolism as it contributes to collagen synthesis, providing the scaffolding for mineralisation using calcium.
Celiacs and CalciumSuch considerations are especially important for those on a gluten-free diet due to Celiac’s disease. This is because calcium is one of the key nutrients that Celiac’s tend to have difficulty absorbing and, as such, they may be told to take a calcium supplement, often of a high dosage. The intestinal absorption problems experienced by those with Celiac’s disease extend far beyond calcium, however, meaning that finding a dietary approach to such problems is often better in the long-term in order to ensure a balanced intake of nutrients. Working with a naturopathically-minded doctor and nutritionist who stays abreast of nutrition research like this is highly recommended.
The Latest Swedish Study on Calcium Supplements and Death
Back to the research in question: 61,433 women had their data analysed for this study, with the oldest participants born in 1914 and the youngest in 1948. Records spanned an average of 19 years, during which time there were 11,944 deaths, including 1100 from stroke, 1932 from ischaemic heart disease and 3862 from CVD. The researchers looked at the food frequency questionnaires filled out by 38,984 of the women and estimated their dietary intake of calcium, along with noting supplements taken. Whilst food frequency questionnaires have significant problems, including reliance on memory and estimation on the part of the subjects, they are helpful in that they are easy enough to do and can gather large amounts of data for such all-encompassing projects. This study has some problems, however, more of which below.
Do Calcium Supplements Double Death Rates?
What the researchers found was that those women with the highest calcium intakes (>1400mg/day) had a higher all-cause risk for death compared to those with intakes of 600-1000mg/day. The relative risk ratio was 1.40 (with the range 1.17-1.67). What this means is that the women consuming 1400mg or more of calcium a day were 40% more likely to die during the study than those taking 600-1000mg of calcium a day (whether through diet or supplements). These figures were adjusted to account for age, total energy, vitamin D, and calcium supplement intake, as well as other dietary, physical, and demographic factors. Ischaemic heart disease (where blood flow is obstructed in the heart) had a relative risk ratio of 2.14 in the highest intake group, and CVD had an RR of 1.49.
Interestingly, the risk of CVD and ischaemic heart disease was also elevated in those ingesting less than 600mg of calcium each day. This could indicate a wider problem of malnutrition and poor health in these patients. Looking at the use of supplements, the women with an intake of more than 1400mg of calcium a day who also took calcium supplements had an all-cause risk of death 2.5 times higher than those with similar intakes but whose calcium came from dietary sources alone.
Do the Numbers Add Up in this Latest Study?
A closer look at the numbers in the study does weaken the findings, however. Just 1241 women fell into the highest intake group and, although all the the deaths in this group occurred in those women taking calcium supplements, there were just 23 deaths recorded. Some 16 of these deaths were women taking any form of calcium supplement, which could be a pretty insignificant dose as part of a multivitamin. However, comparing women in the high intake group who took calcium supplements, with those who didn’t take supplements resulted in a relative risk ratio of 2.57 vs. 1.17, suggesting the conclusion that it is the supplements that are the problem. What else came with the calcium pills is unknown and it may be that the women were taking them because they considered them necessary for other health reasons, such as osteoporosis or a chronic renal (kidney) complaint.
Calcium and Fracture RisksMore physicians are recommending avoiding calcium supplements, especially for patients with osteoporosis as other studies have shown no benefit in fracture reduction in those with the condition who have a high calcium intake. Until further research is done to show safety and efficacy it appears wise to avoid such supplements. Many of the same studies have found that optimal vitamin D intake does correlate with a reduction in fracture risk, however, so be sure to get a dose of sunshine, eat fortified foods and take a daily vegan vitamin D supplement.
The body is incredibly good at regulating blood calcium levels but begins to struggle when intakes are consistently high or low, meaning that calcium deposits may occur in undesirable places with high intake, such as in the arteries bound to cholesterol. Excess calcium can also adversely affect muscle contraction and relaxation, nervous system function and even the function of the thyroid gland, the kidneys and the skin.
In Conclusion: Eat Some BroccoliThe advice from this study, then, is to avoid calcium supplementation if you have a normal and varied diet, but the authors don’t, unfortunately, mention vegans or Celiacs. Making any dietary changes based on a single study is usually unwise but the evidence is certainly stacking up to suggest that optimal calcium intake is better achieved through dietary means, rather than through supplementation. Of course, this does not mean draining a glass of cow’s milk daily as vegan calcium sources are plentiful and come along with magnesium, zinc and other helpful bone-building, heart healthy minerals and vitamins.
Michaëlsson K, Melhus H, Warensjö Lemming E, Wolk A, Byberg L., Long term calcium intake and rates of all cause and cardiovascular mortality: community based prospective longitudinal cohort study, BMJ. 2013 Feb 12;346:f228. doi: 10.1136/bmj.f228.
Warensjö E, Byberg L, Melhus H, Gedeborg R, Mallmin H, Wolk A, Michaëlsson K., Dietary calcium intake and risk of fracture and osteoporosis: prospective longitudinal cohort study. BMJ. 2011 May 24;342:d1473. doi: 10.1136/bmj.d1473.