The Potential Risks of Calcium Supplementation
…Is It Worth the Risk?
TAKE NOTE: This is a subject of which I’m passionate, it could change people’s lives, and there’s a lot of research on it, meaning this post is a bit long. If you don’t have time to read, please scroll to the bottom for the 3 things you should do in response to this information.
The Roles of Calcium, Vitamin D, and Vitamin K
These 3 nutrients are intricately woven, and can be difficult to obtain in sufficient quantities in the typical Western lifestyle. We don’t eat fish with bones, spend hours outside, and ferment our food like humans have done for thousands of years to get calcium, Vitamin D, and Vitamin K. We know bones are made primarily of calcium, and a lot of us are struggling with low bone density, so supplementation has been the norm for decades. More recently, we’ve also discovered we’re all deficient in Vitamin D, which helps our bodies absorb the calcium, so supplementation for it has become commonplace as well.
But it’s not until very recently that we’ve discovered the importance of Vitamin K in helping that well-absorbed calcium make it to the bones and not build up where we are inflamed, such as the arteries. Most medical practitioners are not yet aware that Vitamin K activates both osteocalcin, which grabs calcium to put into the bones, and matrix GLA protein, which prevents calcium’s deposition in the arteries.1 So what happens when there’s plenty of calcium and not enough Vitamin K?
Research Suggests Supplementation Can Be Risky
Scientific studies over the last decade have cast doubt on the role of high-dose calcium supplementation.
- A 2010 Harvard review of 8 randomized trials showed that calcium supplementation alone increased risk of cardiovascular disease (CVD) by 14%, calcium with D by 4%, and D alone decreased risk 10%, though none of these trends reached statistical significance.2
- Later that year, a review of about 12,000 individuals found that in the group given >500mg calcium, there were 190 strokes, whereas the placebo group experienced 156, and there was a 30% increased risk of heart attack for those on the supplement.3
- A 2011 review of 44,790 postmenopausal women found that those given calcium, with or without Vitamin D, had about a 20% increased risk of heart attack or stroke.4
- A German study of 23,980 people over 11 years found a dramatic 86% increased risk of heart attack from calcium supplements, though a decrease in risk from dietary calcium.5
- A UK study of 5,292 people showed that vascular disease mortality was 43% higher in those allocated to calcium supplements, though not statistically significant. This trial was shorter (only 4 years) and had poor compliance, which might have led to the lack of significance.6
- A Finnish study of 10,555 women aged 52-62 found a 24-26% increased risk of being diagnosed with coronary heart disease if they took calcium supplements, regardless if it was with Vitamin D.7
Research is not conclusive, however. Some studies show that with dietary intake in populations that may consume more Vitamin K, increased calcium consumption lowers cardiovascular risk in women while slightly increasing it in men.8 In addition, it appears the amount has a meaningful impact. Drawing from a database of almost 2.5 million patients, researchers in Spain found that calcium supplementation at or over 1,000mg per day more than doubled risk of heart attack whereas less than that amount decreased risk.8
After many hours of pouring over the studies, my takeaway is that dietary consumption has no significant effect on risk, as it tends to come with some Vitamin K when taken in foods, is less absorbable than a supplement, and is typically in smaller doses. The risk seems to be greatest in those who might already get enough calcium in their diet plus supplement with high doses and are not getting Vitamin K as well. Risk also seems to accumulate over time, as shorter studies tend to report smaller effects.
But Wait- Don’t We Need All That Calcium?
Studies of populations that don’t consume dairy because it is not part of their culture don’t actually show an increased risk of fracture. This has caused scientists to look at groups of people and divide them into those who consume the greatest amount of calcium vs the least to see how it effects fracture rates.
- A Korean study of 4,311 men and women found no decreased risk of fracture with increasing calcium consumption from diet.9
- A review of 7 studies observing a population of 170,991 women found no association between total calcium intake (whether diet or supplements) and hip fractures. It also found in 6,504 subjects in clinical trials where 800-1600mg calcium or placebo was given, the supplementation groups had a 64% greater risk of fracture than the placebo group.10
- A large review discovered that the positive studies that showed a small 11% reduced fracture risk with calcium supplementation were found to have high bias, and when limited to studies with no bias, no benefit was found.11 They concluded:
Dietary calcium intake is not associated with risk of fracture, and there is no clinical trial evidence that increasing calcium intake from dietary sources prevents fractures. Evidence that calcium supplements prevent fractures is weak and inconsistent.
If you look at the graph below, it does not show the more calcium you consume, the better your bone density.12 Rather, it shows Vitamin D is the most important factor. Upon looking closer, some studies actually show negative effects of high-dose calcium on bones. A large trial of 77,000 women that were followed for 12 years found that those who drank 2 or more glasses of milk per day had a 45% greater risk of fracture compared to those who drank 1 glass or less per week.13 Furthermore, there was no decrease in fractures from increased calcium intake from other sources. A 2017 review concluded: “In osteoporosis management there is ongoing controversy, though meta-analyses of trial data raise real concern that these supplements carry more risk than benefit.”14
Vitamin K to the Rescue
As I mentioned in the beginning of this post (if you can remember that long ago haha), Vitamin K helps calcium get into the bone and prevents it from accumulating in blood vessels. So maybe the problem is not that calcium is a bad guy, he just needs his chaperone Vitamin K to keep him on track:
- Those who consume the most Vitamin K in their diet may have up to a 70% reduction in hip fracture and are more likely to have higher vertebral bone density.15, 16
- Supplementation with 180mcg/day of Vitamin K2-7 in postmenopausal women increased vertebral strength, density, and height.17
- Studies show that those with atherosclerosis (hardening and calcification of the arteries) have lower bone density and less Vitamin K in their blood.18
- The Rotterdam Study of 4807 subjects found that those with the highest Vitamin K2 dietary intake had half the risk of severe aortic calcification and death from coronary heart disease. K1 did not have an effect.19
- Supplementation with 180mcg/day of K2-7 in postmenopausal women improved arterial stiffness. The more stiff the arteries, the greater the benefit of supplementation.20
What the Experts Recommend
Below are some authors’ conclusions taken right from their scientific studies on how to proceed with protecting both our bones and our heart:
“Thus, calcium in tandem with vitamin K2 may well be the solution for bringing necessary bone benefits while circumventing an increased risk for heart disease.”1
“To summarise, the following steps may be helpful for building strong bones while maintaining soft and supple arteries: (1) calcium is best obtained from dietary sources rather than supplements; (2) ensure that adequate animal protein intake is coupled with calcium intake of 1000 mg/day; (3) maintain vitamin D levels in the normal range; (4) increase intake of fruits and vegetables to alkalinise the system and promote bone health; (5) concomitantly increase potassium consumption while reducing sodium intake; (6) consider increasing the intake of foods rich in vitamins K1 and K2; (7) consider including bones in the diet; they are a rich source of calcium-hydroxyapatite and many other nutrients needed for building bone.”12
Myself and my patients are not particularly excited about the recommendation to eat bones, therefore I recommend a calcium hydroxyapatite supplement with 400-500mg calcium along with Vitamins D and K. This way, with an average of 400mg calcium from the diet, total daily intake is a maximum of 900mg which seems to be the right amount to provide benefit without being too much to possibly increase risk, in a person with sufficient Vitamin K levels.
Summary: Calcium supplementation on its own or with Vitamin D may increase risk of heart disease, so always supplement Vitamin K2-7 with it. The hydroxyapatite form of calcium has good evidence of effectiveness. Avoid high-dose supplementation (1,000mg+). Focus on lifestyle to keep your bones and arteries healthy.