For many years, a popular “chorus of wisdom” about calcium and bone
health has been playing. Its refrain goes something like this: Calcium is essential
to bone health. Variations on this theme are also heard. Drink your milk for
healthy bones... Take a calcium-based antacid, and it will help your bones while
it soothes your stomach... Look, this food, or that one, is fortified with calcium
for healthier bones! In the well-known “Got Milk?” campaign,
one ad has Superman promising “bones of steel” if you drink milk!
This focus on calcium as the “silver bullet” for bone health is not
entirely restricted to mass media marketing messages. You’ll see calcium emphasized
in osteoporosis web sites and pamphlets, research reports, and even in the Surgeon
General’s bone health recommendations. In our society, where calcium is so
widely available and its benefits are so widely known bone disorders like osteoporosis
(fragile bones) and osteopenia (reduced bone mineral density) are still prevalent.
Why is this?
The reasons for this paradox fly in the face of popular understanding: bone loss
is not caused by low calcium intake. Furthermore, calcium by itself will prevent
neither bone loss nor needless osteoporotic fractures.
Bone health depends not so much on calcium intake, but rather on its metabolism
and utilization. The major players in this regard are vitamin D, vitamin K, and
magnesium — which are woefully under-publicized in the campaign against osteoporosis.
This article will discuss these nutrients, and help you understand how critical
they are for maintaining bone health.
Good dairy-free sources of dietary calcium
- Whole wheat products
- Vegetables in the brassica family —
broccoli, kale, cabbage (e.g., bok choy)
- Dark leafy greens, e.g., collards, spinach, turnip greens, dandelion greens, mustard
greens, beet greens
- Canned fish/crustaceans with bones, e.g., sardines, pink salmon, and shrimp
- Beans/legumes, e.g., edamame, tofu, tempeh, black-eyed peas, and black beans
- Nuts and seeds, e.g., almonds, sesame seeds
- Mineral water
- Herbal teas and infusions, e.g., oatstraw, nettle, red clover
Calcium’s role in bone health
Calcium is the most abundant mineral in the human body and has several important
functions. Two percent of our total body weight is made of calcium, and more than
99% of total body calcium is stored in the bones and teeth, where it supports their
structure. The body gets the calcium it needs for everyday, minute-to-minute physiological
functioning in two ways. One way is from the intake of calcium-rich foods. Yes,
these include dairy products, which have a high concentration per serving of highly
absorbable calcium, but also many, many other foods, such as dark, leafy greens,
nuts, beans, and seeds, which have varying amounts of highly absorbable calcium
When blood levels of calcium drop too low and dietary calcium intake is insufficient,
the body will obtain calcium by extracting it from the bones. Ideally, calcium that
is taken from the bones will be replaced when calcium levels are replenished. But
before you reach for that glass of milk, realize that to replace the calcium in
your bones, an intricate process involving intake, metabolism, and utilization must
This is the crux of the myth — while calcium is clearly important, there are
at least 19 other key nutrients that each play a vital role in the structural integrity
and overall health of our bones. To put the larger picture in context, I find it
is sometimes useful to think of bone as a brick wall where the bricks are made of
calcium and the other key nutrients make up the mortar. Without mortar, the wall
is unstable. Bricks may fall out, making the wall even weaker. Just like a brick
wall without mortar, without vitamin D, vitamin K, and magnesium, bone will lose
So, let’s turn our attention to the major players to understand their role
in the process.
Calcium and vitamins D and K and magnesium
The last few years have witnessed a virtual explosion of research on vitamin D.
We now know that this “sunshine vitamin” plays a key role in the prevention
of many chronic diseases, including cancer, heart disease, diabetes, autoimmune
disease, and osteoporosis. When it comes to bone, we now know that vitamin D is
the key to calcium absorption. To paraphrase noted vitamin D researcher Dr. Michael
Holick, you can swim in calcium and it will do no good unless you have adequate
vitamin D. Specifically, without vitamin D your body can only absorb 10–15% of dietary
calcium — so even if calcium is present, the body can’t use it! When
vitamin D is added, the absorption of dietary calcium increases to 30–40%. So, both
calcium and vitamin D are necessary to prevent osteoporosis — including postmenopausal
Most Americans don’t get enough vitamin D — especially during the winter
months, when there is less sunlight. Certain people may also be at a high risk for
vitamin D deficiency, including the elderly, the obese, dark-skinned individuals,
teenage girls, those who spend little time outdoors, and those who regularly use
sunscreens. Because it is a fat-soluble vitamin, vitamin D deficiencies also occur
in people with fat malabsorption syndromes such as in celiac disease, cystic fibrosis,
and inflammatory bowel disease.
Calcium and vitamin K
We have recently learned that Vitamin K is critical for calcium utilization and
regulation. Vitamin K helps proteins bind to calcium and transports them to where
they are needed in bones, organs, and other tissues. Vitamin K is also needed in
the bone to produce a protein called osteocalcin, which, as the name suggests,
helps bind calcium to the bone.
Low vitamin K status is associated with higher levels of bone turnover and increased
fracture risk, while adequate levels of vitamin K have been shown to protect against
a loss of calcium in the urine. French researchers have noted in their studies that
low vitamin K status predicts the subsequent risk of hip fracture. So without adequate
vitamin K, more bone is lost and fracture risk increases. While vitamin K deficiency
is common among all ages, studies show that younger adults and postmenopausal women
tend to have particularly low levels of vitamin K.
Calcium and magnesium
Overall, and through many mechanisms, magnesium is needed for calcium absorption
and bone formation. Magnesium is an essential cofactor in 80% of all cellular enzymes
— including the thyroid hormone calcitonin, which regulates bone
turnover. Magnesium is also needed by the liver enzymes that convert vitamin D into
its active form, known as calcitriol. Recall that vitamin D is needed for
proper calcium absorption — and magnesium deficiency can lead to a syndrome
known as vitamin D resistance. The activity of another critical enzyme for bone
formation, alkaline phosphatase, also depends on magnesium. This enzyme
is needed to solidify calcium and other soluble factors into bone. In fact, much
of the body’s magnesium (60%) is stored in the bone, and it is released into
the blood when it is needed by other tissues. Magnesium deficiency is known to impair
parathyroid hormone secretion and action, and contributes to the development of
osteopenia bone fragility.
While it is extremely important to maintain an adequate magnesium intake, most US
adults consume less than 68% of the daily requirement of this mineral. With all
the roles magnesium plays in bone formation, it is not surprising that even a mild
deficiency is considered to be a leading risk factor for osteoporosis.
It matters what kind of calcium you get
Calcium comes in many different forms. Even with the other nutrients needed for
its absorption, some forms are not as readily absorbed as others. Women often ask
me, “What about this or that type of calcium?” With all the different kinds of calcium
supplements available, how do you choose, and how should you take them? Use the
following points as a guide:
- Calcium citrate is a highly absorbable calcium compound. This form does
not require the hydrochloric acid (HCl) in the stomach to be absorbed. Thus, calcium
citrate is very readily absorbed or bioavailable, and a good choice for people with
low stomach acid.
- Calcium ascorbate and calcium carbonate are generally not as easily
absorbed as the citrate forms if stomach HCl is low. However, they are absorbed
quite readily when taken with food.
- Generally speaking, all types of calcium are absorbed more easily if taken with
meals — no matter what form you choose.
I am sometimes asked my thoughts about microcrystalline hydroxyapatite
(MCHC), an interesting calcium-containing substance derived from animal bones. This
supplement may have its merits (especially for older people, perhaps, with very
low-phosphorus diets, or those who don’t get enough meat or protein — which are
not problems for the average American). It is quite costly, its amino acid content
varies depending on how it’s processed, it does not contain magnesium, and there
are actually few supportive studies on it. So all in all, I do not think microcrystalline
hydroxyapatite is “way superior” to other forms of calcium, and perhaps the premium
on it may be somewhat misplaced.
Regardless of what form you choose, calcium supplements (even MCHC) should always
be balanced with magnesium. I recommend supplementing with at least half
as much magnesium as calcium (a ratio of one part magnesium to two parts calcium),
but my preference as a clinician is for nearly as much magnesium as calcium. People
with inflammatory changes such as osteoarthritis, in particular, want to use equal
amounts of magnesium and calcium (1:1). Some bone specialists even favor magnesium-centered
formulations with equal or slightly more magnesium than calcium.
Though bioavailability differs among different calcium forms, the type of calcium
you choose may not be as hypercritical as your body’s own ability to absorb
it. This depends on a complex interplay of hormones, nutrients, and other factors.
Besides vitamin D, vitamin K, and magnesium, there are numerous other nutrients
that help support your bones (see our detailed page on
20 key nutrients). Moreover, the body’s innate ability to absorb calcium
will vary significantly from one person to the next. One prominent calcium researcher
has determined that people’s ability to absorb different kinds of calcium
can vary up to threefold!
The dairy dilemma
Here in America, the popular-wisdom solution to our calcium needs is to eat lots
(and lots!) of dairy products. Milk products are high in calcium — as everyone
who has seen the ubiquitous milk-mustache posters knows — so it seems to make
sense to drink plentiful milk or eat yogurt, cheese, and ice cream.
There are two problems with this logic: first, there are many people who are lactose
intolerant or otherwise sensitive to proteins in milk, which means that they have
trouble digesting it and aren’t necessarily absorbing all that calcium. And
second, dairy products generally are acid-forming foods, which means that taken
in excess, and without counterbalancing alkalizing foods, they tend to promote a
pH imbalance in the body that leads to further calcium loss from the bones (see
our article on pH for bone health for a full explanation). So while dairy products
do contain a great deal of calcium, dairy alone does not provide the “quick
fix” to bone health many Americans assume it does — and if you rely
solely on dairy’s calcium for bone health, you could be in for a letdown!
A balanced approach — how to make calcium work for your bones and your body
Here are some guidelines for making calcium work to strengthen your bones:
- Rebalance your calcium intake. There are many calcium-rich vegetables
that do double-duty for the bones by alkalizing the system. Beans and other legumes,
such as soy, as well as fish, seeds, and nuts offer additional choices. See the
table above for some of our favorite nondairy calcium-rich foods.
- Let the sun shine in! Our bodies were meant to be exposed to sunshine
— but do this in a way that is health-enhancing, not harmful — see the
section on healthy sunbathing in our vitamin D article for guidance. This will allow
your body to make adequate amounts of vitamin D3 (cholecalciferol).
- Supplement with vitamin D. For maintaining adequate levels of vitamin
D, 1000–2000 IU per day is safe and adequate. If you think you could be vitamin
D-deficient — as are some billion people worldwide — ask your healthcare
provider for vitamin D testing, then supplement accordingly. See our page on vitamin
D testing and treatment for some answers to common questions about this test and
how to interpret your results.
- Increase your intake of vitamin K. Most people get some, but not
enough vitamin K from their diet (from green leafy vegetables and fermented foods
like aged cheese). As a whole, however, we consume suboptimal amounts of this key
bone nutrient. For optimum bone health, supplementation with vitamin K2 is recommended
for nearly everyone. Exceptions include those using the blood-thinning drug Coumadin
(warfarin), as this vitamin can interfere with the action of blood-thinner drugs.
Again, dairy is a fine addition to your bone health regimen — if tolerated
— but we urge you not to think of it as the centerpiece. And if you do enjoy
dairy foods, we encourage you to choose those that are organically produced. You
and your bones do not need the hormones or pesticide and antibiotic residues found
in conventionally produced milk — and organic dairy products are now widely
More than just the milk mustache
When it comes to whole-body health, there are few “silver bullets” —
and calcium isn’t one, either, though it is undeniably important. Historically
and throughout the world today, there are many cultures whose bones remain strong
throughout the lifespan without the overemphasis on dairy foods commonplace in America
today. By thinking of calcium as only part of a well-rounded, alkalizing diet and
lifestyle, you, too, can create better bones — and a better body!
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