Dr. Steven Chaney reviews the recent studies behind the sensational news stories about calcium supplementation and death.
Should men avoid calcium supplements? Should women
avoid calcium supplements? Do calcium supplements
increase heart disease risk? If you’ve been listening
to some of the recent headlines in magazines,
newspapers and health blogs, that’s exactly what you
might think. And, after years of telling us that
calcium supplements may be important for bone health,
even some doctors are now recommending that their
patients avoid calcium supplements. So what’s the
truth? What should you believe?
Let’s start by examining the existing research. The
latest headlines are based on a JAMA article (Xiao et
al, JAMA Internal Medicine, 173: 639-646, 2013) that
concluded that high calcium intake from supplements was
associated with a slight (20%) increased risk of
cardiovascular death in men, but not in women. Another
study (Michaelsson et al, BMJ, 2013:346 doi:
10.1136/bmj.f228) published earlier this year concluded
that high calcium intake (> 1,400 mg/day) was
associated with an increased risk of cardiovascular and
all cause death in women, but not in men. In this study
calcium supplementation was also associated with an
increased risk of death, but only in women with a total
calcium intake greater than 1400 mg per day.
Of course, the press always likes to hype the latest
study, especially if that study is bad news. So let me
help you evaluate that report the way that a scientist
would. To begin with one of those studies concluded
that calcium supplementation is associated with
increased cardiovascular death in men, but not in
women. But, the other study concluded that calcium
supplementation is associated with increased
cardiovascular death in women, but not in men. That’s a
bit curious. Obviously, both studies cannot be correct.
So what does a scientist do when confronted with
conflicting studies? We dig a bit deeper into the
literature and asking what other studies say. And. when
I dug further into the literature, things got even
murkier. It turns out that both of those studies are
contradicted by other, equally good, clinical studies.
For example, two major studies have found no
correlation between cardiovascular death and either
dietary or supplemental calcium intake (Li et al,
Heart, 98: 920-925, 2012; Bolland et al, BMJ, 342:
d2040, 2011). And, another study reported that both
increased dietary intake of calcium and use of calcium
supplements were associated with a reduced risk of
death in women, but not in men (Langsetmo et al, J.
Clin. Endocrin. Metab., doi: 10.1210/jc.2013-1516).
Faced with all the conflicting published clinical
studies, the Institute of Medicine recently concluded
that “evidence from clinical trials currently does not
support an effect of calcium intake on risk of
cardiovascular disease”.
Are you confused yet? If so, you have every right to
be. The experts in their field are also scratching
their heads.
So let me add to your confusion by sharing with you yet
another study that has just been published (Van
Hemelrijck et al, PLOS One, April 2013, volume 8, issue
4, e61037). This study looked at 20,024 adults 17 years
old and older who were surveyed in the third National
Health and Nutrition Examination Survey (NHANES III).
The study asked how many of them died of cardiovascular
disease over the next 12 to 18 years. The strength of
this study is that it evaluated serum calcium levels as
well as dietary and supplemental intake of calcium. In
this study only serum calcium levels showed any
correlation with cardiovascular death – and even this
effect was confusing. For women there was an increased
risk of cardiovascular death for those with serum
calcium levels in the top 5%. In contrast, for men
there was an increased risk of cardiovascular death for
those with serum calcium levels in the bottom 5%. Once
again, no association was observed with cardiovascular
death and either dietary or supplemental calcium
intake.
The reason I’m bringing this study to your attention is
I think it may offer a key to understanding the
conflicting results of previous studies. Serum calcium
levels are very tightly regulated by the body and are
not normally affected by either high or low calcium
intakes. For example, in the study above there was no
correlation between serum calcium levels and either
dietary or supplemental calcium intake. Significant
variations in serum calcium levels are usually
associated with either metabolic or hormonal diseases.
Perhaps some of the conflicting results in the
previously mentioned studies may be due to inclusion or
exclusion of people with diseases that affect serum
calcium levels. I will hasten to add that this is just
a hypothesis on my part – one that needs to be verified
by further studies.
So what is the bottom line for you?
1)The evidence that calcium supplementation affects
cardiovascular risk is weak at best. While the
possibility of increased cardiovascular risk associated
with high calcium intakes exists, the preponderance of
evidence suggest that this is not a concern, despite
what many of the recent headlines suggest.
2)On the other hand, there is clear evidence that
calcium intake in the 1000 to 1300 mg per day range
decreases the risk of osteoporosis, and osteoporosis
can significantly decrease the quality of life and even
lead to increased mortality. Most people aren’t getting
enough calcium in their diet. For these people
appropriate calcium supplementation is clearly
advantageous.
3)So my advice is to ignore the scary headlines and
continue to make sure that you’re getting the 1000 to
1300 mg of calcium per day that you need for healthy
bones. I will keep you updated if the science about
cardiovascular risk changes.
4)Of course, you don’t need to go overboard on
supplemental calcium. Start by figuring out your
dietary calcium intake. You can count on about 200 to
250 mg per serving for most dairy products, and most
people get around 200 mg per day of calcium from other
food sources. Once you’ve figured out your dietary
calcium intake, add enough supplemental calcium to
bring your total intake up to the recommended RDAs
(1,300 mg/day for ages 13-18, 1,000 mg/day for ages
19-50, and 1,200 mg/day for adults over 50).
5)Finally, as I have told you previously, supplemental
calcium is unlikely to do mischief if it is utilized
primarily for bone formation, so make sure that you are
getting 800 to 1200 IU of vitamin D per day plus RDA
levels of the other nutrients needed for bone formation
(vitamin C, vitamin K, magnesium, zinc, copper and
manganese).
To Your Health!
Dr. Stephen G Chaney
May 2013