Recently I heard someone state that milk was not a good source of calcium because the calcium is not well absorbed. When I inquired further she later changing the specifics, claiming the animal protein contained in milk causes more calcium to be lost via the kidneys (urine) than is provided by the milk.
I have previously pointed out that this theory (animal protein in the form of meat causes net calcium loss) is absolutely false and without any supporting evidence when clinically tested (see link here). Still, I wanted to look for studies specifically on milk to see if, like meat, it didn’t worsen calcium balance as this person claimed.
The Effect of Dairy on Calcium Balance and Indicators Bone Health
In 1985, two doctors named Robert, last names Recker and Heaney, published a paper in which 13 female participants consumed 24 ounces of milk per day for a year (1). These milk drinking women experienced improved calcium balance compared to a non milk drinking control group. The effects of milk in this study were comparable, and in some ways seemingly better, than the effects of a calcium carbonate supplement used in a previous study carried out by the same researchers.
These Roberts would later carry out studies in which they compared the absorbability of calcium from various foods to milk in human volunteers. These studies, performed in 1988 (2), 1990 (3), and 1997 (4) would report that calcium absorption from milk is much greater than from spinach, rhubarb, and sweet potatoes and slightly less than that of kale, mustard greens, and cabbage flower leaves. Thus, it would seem, at least as absorption goes, that milk is neither an exceptional nor a poor source of calcium.
Certainly doesn’t seem like milk has poorly absorbable calcium.
Additionally, two randomized controlled trials lasting 16 weeks found that among overweight adults undergoing weight loss, those randomized into a high protein, high diary diet had better markers of bone health (e.g. lower deoxypyridinoline, N-telopeptide, etc.) than control groups eating lower protein, lower dairy (and thus lower calcium) diets (5,6). One of these studies also found that following a diet higher in diary (and calcium) but equal in protein also led to comparably better levels of bone resorption markers (6).
Two other randomized trials carried out by a group of researchers led by Robert Heaney (abandoning his fellow Robert! What happened? Did they have a falling out? All this and more on the next episode of….uhh sorry) reported that, among older folks, adding milk (20) and yogurt (21) improved short term markers of bone health (i.e. urinary N-telopeptide).
Okay, maybe you’re saying to yourself:
“Wait a minute, I’m just a simple country lawyer, I don’t even know what ‘bone resorption’ means. Can you reeallly figure out how good something is for someone’s bones by taking their pee and measuring a bunch of things I’ve never heard of? Those studies talk about N-telopeptide, carboxy terminal cross links, osteoprotegerin, alkaline phosphatase….that all sounds like some mumbo jumbo!”
Settle down, friend. If you’re not convinced by those studies, we’ll cut to the chase and look at studies where they ultimately just tested the bones themselves to see how strong they were. Hard to debate those kind of measurements.
The Effect of Calcium From Dairy on Bone Mineral Density
A study conducted in 2008 recruited 130 overweight men and women and had half of them follow a diet high in protein, especially diary products, while the other half followed a diet higher in carbohydrates, particularly starchy foods (7). After 12 months those following the diet higher in protein and dairy had greater bone mineral density and content of the hip, lumbar spine, and whole body compared to the other group.
Another study recruited older Chinese women to either consume milk powder or continue their diet as usual (8). After 24 months the women consuming the milk powder experienced less bone loss in their lumbar spine, femoral neck, hip, and entire body compared to the women following their usual diet.
Two additional studies using young girls as subjects (one on early teens the other on late teens) saw bone mineral density and content improve when subjects consumed dairy products compared to a control group not doing so (9,10).
Finally, a 2 year study on older men found that participants taking milk and whey (a milk protein) supplements slowed bone loss compared to a control group not taking the milk and whey (11).
Okay, I think I’m making my point now.
Still, perhaps you’re conceding that milk can be a good source of calcium, but you’re not convinced it’s the best source of calcium. Maybe if you gave people a comparable amount of calcium as was provided by milk in the above studies they would be even better off? Alright well let’s see if that’s true.
Getting Calcium From Diary Versus Non-Dairy Sources
A study on older women studied the effects of taking different calcium sources on bone health compared to a placebo, specifically milk powder and calcium supplements (12). At the end of the 2 year trial each calcium source produced similar effects on bone lose and gain at all sites examined, with both calcium sources showing equal benefit compared to the placebo group.
A study with a similar experimental set up to the prior one, with 10-12 year old girls as participants, compared an equal amount of calcium from cheese to calcium from supplements in the form calcium carbonate (13). At the end of this 2 year trial the girls in the cheese group saw generally greater increases in bone than those in the calcium and placebo group, though this was only significant for the cortical thickness of the tibia. The authors of the study ultimately concluded:
“Increasing calcium intake by consuming cheese appears to be more beneficial for cortical bone mass accrual than the consumption of tablets containing a similar amount of calcium”
It would seem dairy products do not impair the utilization of the calcium they contain and are a perfectly acceptable source of calcium.
With seemingly every aspect of this myth shot down, we turn to one additional claim sometimes used to make dairy seem like not a great source of calcium; people with lactose intolerance can’t digest it and therefore might not be able to absorb the calcium. That makes sense, right?
Lactose Intolerance and Dairy Calcium Absorption
First of all, if you are lactose intolerant you probably shouldn’t be drinking lactose containing foods like milk. Isn’t that a no brainer?
Either way, this question has been tested and the results are mixed. Some studies have found lactose impairs calcium absorption in lactose intolerant individuals (14-16) while other studies have found no such impairment (17,18) or, surprisingly, better calcium absorption (19). Additionally, none of the studies showing impairment even demonstrate milk to be a poor source of calcium, just not as good as if the subjects could produce their own lactose.
So there you have it. If you are lactose intolerant you still probably shouldn’t consume milk (I think we all no people with lactose intolerance who drink milk anyway and c’mon, nobody wants that kinda booty stank around). But for whatever it’s worth, there still doesn’t appear to be evidence that milk is a poor source of calcium for lactose intolerant individuals.
If it wasn’t already clear, milk is definitely a good source of calcium and saying otherwise is the nutrition equivalent of saying every moon landing was faked and never actually happened. If someone repeats this myth as if it were fact they, in my humble opinion, have lost all credibility and all further information they state about nutrition should be considered highly questionable.
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2. Heaney RP, Weaver CM, Recker RR. Calcium absorbability from spinach. Am J Clin Nutr. 1988 Apr;47(4):707-9. PubMed PMID: 3354496
3. Heaney RP, Weaver CM. Calcium absorption from kale. Am J Clin Nutr. 1990 Apr;51(4):656-7. PubMed PMID: 2321572
4. Weaver CM, Heaney RP, Nickel KP, Packard PI. Calcium Bioavailability from High Oxalate Vegetables: Chinese Vegetables, Sweet Potatoes and Rhubarb. Journal of Food Science. 1997, 62(3):524-525
5. Bowen J, Noakes M, Clifton PM. A high dairy protein, high-calcium diet minimizes bone turnover in overweight adults during weight loss. J Nutr. 2004Mar;134(3):568-73. PubMed PMID: 1498844
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