Are calcium supplements a health risk?
Like many other women, I’m paying attention to my calcium intake. I’m making a conscious effort to boost intake with a combination of food sources and supplements. Actually make that “supplement”. I take one 300 mg pill a day, usually. As calcium citrate, not carbonate (the more common pill form). 300 mg is about the same amount in a typical serving of a dairy food like milk or yogurt. My average intake probably doesn’t meet the official government recommendation of 1000 mg/day. So, when I saw the news about the latest research slam at calcium supplements, I wanted to know more. After reading through the actual research paper I’m more confused than ever.
You have to think if a research report is confusing to a nutrition professional, it’s probably incomprehensible to your average MSM journalist trying to attract readers. Of course, scary headlines are catnip to readers. Plenty of people read only the headlines, and it’s pretty easy to conclude that calcium is a dangerous substance from the recent headlines. Apparently calcium supplements cause heart attacks! Acckkk! What’s a woman to do?
First some basics:
- Calcium is essential to life. It’s a key component of bone structure and plays an important role in many metabolic systems, including muscle contraction
- High calcium foods include dairy foods, legumes, dark greens, tofu and some fortified foods, like soy milk.
- Supplements are popular, especially for people who need to boost intake for bone health, but don’t want to be bothered with dairy foods.
- Calcium in supplements comes in different chemical forms: carbonate, citrate, gluconate, lactate. Sometimes these come in combination with other bone nutrients like magnesium, vitamin D or vitamin K
- Blood calcium is always maintained within a certain narrow range. If you don’t eat enough to maintain that range, your body draws calcium out of bones to maintain that blood level.
What about if you consume extra calcium? Ideally it would be incorporated into bones. That would be especially important for people with thinning bones. But according to this study, there may be other less desirable destinations, such as blood vessel walls. Calcification of blood vessels, such as coronary arteries, is a risk factor for heart disease. Calcium deposits don’t belong in blood vessel walls. They cause vessels to be less flexible and more prone to plaque build up.
Cue the latest study, which was designed to look at calcification of coronary arteries over a 10 year follow up period. The study followed a large group of older people for 10 years. They were evaluated at the beginning of the 10 year period for calcium intake, coronary artery calcification and a range of other measurements including height, weight, blood lipids, blood glucose, blood pressure and on and on. Dietary calcium was evaluated using a food frequency questionnaire, which right away raised red flags for me. They’re not terribly reliable. A food frequency questionnaire is a very long list of foods. Respondents have to answer how often they eat each food. Say you enjoy cantaloupe melon in late summer, when they’re ripe. Let’s say the listing for melon gives you these choices:
- 2-3 times a week
- once a week
- once a month
What on earth do you say if you just eat melon during August, but eat it 3 times a week? Do you start doing the math in your head: “let’s see, 3 times a week for 5 weeks divided by 52 weeks in a year, yadayadayada….” Or do you give up and say “never”? At which point the nutrients in melon (vitamin C, potassium, etc) are lost data.
Let’s say you don’t really drink milk, but maybe you have a bit in your coffee every morning, or sometimes have it on cereal. So you answer “daily”, that sounds good. And you over-estimate the portion size. Now for the purposes of this study, your calcium intake has been inflated.
Subjects also provided information about calcium supplement use at the beginning of the 10 year study period. It’s not clear this information was gathered again 10 years later. If not, then how do we know those thousands of people stuck with the exact same supplement regimen for 10 years?
The one thing that was measured twice is coronary artery calcification. At the end of the 10 year period, many of the subjects had increased calcification. While this is not good, it didn’t mean they had heart attacks, just that risk had increased. Did increasing calcium intake lead to increasing calcification? No, not exactly. According to the study authors, the people with the highest calcium intakes from food and supplements had the lowest risk for coronary calcification. But they also managed to conclude that supplementary calcium was linked to more calcification over the 10 year period than dietary calcium. What level of supplementation was supposedly a problem? It’s not clear. In my professional opinion, this study has plenty of limitations:
- Not assessing calcium intake from food and supplements on a regular basis throughout the 10 year study
- Use of food frequency questionnaire
- Not accounting for 10 years of other diet and lifestyle factors that impact arterial calcification and heart disease risk
- Not accounting for the different types of supplements people use
- Not accounting for the type of people who rely on supplements. This to me is a huge flaw. There are lots of people who use supplements as a substitute for good diet choices. And there are people who may be relying on calcium supplements because they don’t like or can’t tolerate high calcium foods. So perhaps something else about these people increases risk for arterial calcification that has nothing to do with simple calcium intake.
At best we know that some of the study subjects had more arterial calcification 10 years later. Nothing I read convinced me to change my plan. I’m going to continue taking a supplement daily while also focusing on high calcium foods. I don’t recommend calcium supplements as the be-all-end-all to boost calcium for a lot of reasons, primarily all the other nutrients in foods. People who rely on supplements to make up for a bad diet aren’t doing themselves any favors, whether it’s calcium or B-vitamins or vitamin C.
My Take Away Message: the definitive study on the link between calcium supplements and heart disease risk has not been done.