Confused about all these conflicting studies on calcium use? How some studies seem to say calcium is good, then others say it’s bad? (What else is new, right?)
Researchers writing in the American Journal of Clinical Nutrition did a novel analysis that may shed some light.
First, some background.
The Women’s Health Initiative was a big famous study of hormone therapy. Many of the participants were also asked to simultaneously take part in a dietary modification trial that was a kind of “sub-section” of the larger study. This section of the Women’s Health Initiative was called the Women’s Health Initiative CaD trial, with CaD standing for Calcium/ vitamin D.
In the CaD trial, 36,282 postmenopausal women aged 50-79 were randomized into one of two groups. Group one took 1,000 mg of calcium carbonate and 400 IUs of vitamin D daily. The second group got a placebo. The participants were then followed up for between 7-11 years.
(Quick comment: Notice that the form of calcium they gave was calcium carbonate, which could have made a difference to the outcome. Calcium carbonate is the calcium used in Tums. It’s the cheapest kind of calcium, but it comes with the most caveats, one of which is that it needs to be taken with food, because it depends upon stomach acid for its absorption. But since we make less stomach acid as we grow older, calcium citrate is the recommended form of calcium for older people. The women in this study were between 50-79 years old. Just sayin’.)
Overall, that study reported that the calcium/ vitamin D supplements had no effect on the incidence of hip or total fractures, cardiovascular outcomes, colorectal or breast cancer, or mortality.
Well, you might think, so much for all those claims for calcium and vitamin D. Not a whit of an effect on anything we care about- not bones, not the heart, not cancer, not dying.
If you didn’t look any further, you might be tempted to dump your calcium supplements, maybe even your vitamin D caps just for good measure.
Not so fast.
In randomized controlled trials, calcium/ vitamin D supplements administered individually or in combination decreased recurrent colorectal adenomas, reduced the risk of cancer, reduced the risk of mortality. Unfortunately, other studies showed that calcium supplements given alone increased the risk of myocardial infarctions (heart attacks)!
Which brings us to the new study.
A noteworthy feature of the Women’s Health Initiative Calcium and Vitamin D study (CaD) was that many of the women in the study were taking calcium and/or vitamin D supplements on their own when the study started. Realizing this, researchers separated the women into two groups—those who were taking supplemental calcium and or vitamin D on their own at the start of the study, and those who were not.
Here’s where it gets interesting.
In participants who were already taking calcium and/or vitamin D supplements at the start of the study, taking the 1000 mg of calcium and 400 IUs of vitamin D given during the study proper didn’t have any affect on cancer.
But for women not taking personal supplements of calcium and/or vitamin D when the study started, giving them their 1000 mg of calcium and 400 IUs of vitamin D significantly reduced their risk of total cancer, breast cancer and invasive breast cancer by 14-20% and nonsignificantly reduced colorectal cancer by 17%.
The bad news is that the 1000 mg of calcium and 400 IUs of vitamin D did increase the risk for cardiovascular events by 13-22%, but, strangely, only in the women who were not taking these supplements on their own at the start. For the women who were, the extra calcium and vitamin D didn’t add any risk. The researchers are pretty sure- as am I- that any increased risk for heart trouble comes from the calcium, not the vitamin D, as the risk seen in this study for the combo vitamin treatment was just about identical to the additional risk seen for calcium alone.
This re-analysis shows how a really beneficial effect of vitamins in any study can easily be obscured by factors like what the subjects were doing on their own, or what their nutritional status was at the start of the study. For example, calcium was long touted by the dairy industry for weight loss, but it turns out any weight loss benefit for calcium is only seen in people who are calcium deficient to begin with; calcium has no weight loss benefit if you’re already getting enough, despite those ridiculous ads showing women with 3% body fat eating fruity yogurt-y junk food and claiming their fabulous bodies are all due to the calcium in the yogurt.
But I digress.
This current study has some puzzling results—like why did the women already taking calcium and vitamin D at the start of the study have no additional risk for heart disease when they took the supplements given in the study, but the women who were supplement virgins did? Very strange.
I think the safest conclusion to make from all of this is that calcium has an overall beneficial effect but should never be taken alone.
Rather, take it in a good bone formula that contains all the synergistic nutrients like vitamin D, magnesium, boron, silica, manganese and vitamin K (or as many of them as possible).
And relax a bit on the dose. I think it’s only a matter of time before the powers that be pull back on their recommendations that every women get between 1000-1500 mg of calcium a day. First of all, many people believe that recommendation means you should take 1000-1500 mg of calcium supplements every day, and the recommendation is actually for total calcium. Drinking a lot of milk (not my favorite choice unless it’s raw) or eating a lot of yogurt definitely reduces the amount you need from supplements.
Second of all, you may not need as much calcium if you cut back on some of the calcium-robbers in your diet. Phosphoric acid from sodas, for example, will leech the calcium right off your teeth. (OK, not really, but it’s a good image.) Sugar is another calcium-robber. If there’s not a leak in the bathtub, you may not have to keep adding so much water, you know?