From: young@clpd.kodak.com (Rich Young)
Subject: Re: Milk and calcium (here we go again)
Originator: young@sasquatch
Reply-To: young@clpd.kodak.com
Organization: Clinical Diagnostics Division, Eastman Kodak Company
Date: Sat, 23 Jan 93 17:41:54 GMT

In article <1993Jan23.034204.23411@leland.Stanford.EDU> coleman@leland.Stanford.EDU (Michele Coleman) writes:

[...]

>    What about all those places in the world where people don't drink
>milk at all, like parts of Africa and Asia?  How do women there fare?

	Generally, they have a lower incidence of osteoporosis, but it's
	dangerous to automatically assume that this is completely attributable
	to diet.  Blacks, for instance, are known to have bone densities
	which are as much as 10 percent greater than Orientals or Caucasians.
	This is genetic, not environmental.  Another confounding factor is
	exercise: strenuous physical activity is known to strengthen bones,
	regardless of diet, and Asians may be getting much more exercise
	than the typical American.  There are other factors which tend to
	cast some doubt on epidemiological studies which rely on fracture
	rates to evaluate bone strength: for example, Western society
	uses the automobile far more often than most African and Asian
	societies, which means more accidents, which in turn means more
	fractures.

	It may be possible to correct for these factors in a well-run 
	epidemiological evaluation, but it is incumbent upon the reader
	to verify that such factors as these have, in fact, been taken into
	account in any data presented.  Another point to keep in the
	very front of one's mind is the fact that "correlation" does not
	necessarily mean "causation."  A perfect example is a chart
	presented by Dr. John McDougall in "McDougall's Medicine" which
	shows hip fractures per 100,000 population for a group of varied
	populations.  He claims a high correlation between consumption
	of animal protein and hip fractures...he neglects to mention that
	the correlation is almost identical with life expectancy at birth.
	So, which causes the hip fractures: consumption of animal protein or
	old age?

>Does this osteoperosis thing appear in other mammels--that would be
>interesting to know.  Elephants and moose seem like they have an awful
>lot of bone--so where does all that calcium come from?  The soil must be
>chalk (sorry) full of it.

	One must be very cautious in drawing conclusions about humans
	from observation of other mammals.  Diets differ significantly,
	digestion often differs markedly, and living habits may be
	completely at odds with human practices.

	Bears, for example, experience no net loss of bone minerals while
	they undergo extended periods of inactivity during their winter
	sleep, but humans lose significant bone mass in just a few days
	in outer space.  Elephants and moose eat twigs and bark (among
	other things), both of which are utterly indigestible to humans.
	Interestingly, both of these animals, especially elephants, are
	known to travel some distance to reach "mineral licks" at which
	they supplement their diets by licking and eating exposed mineral
	salt deposits, which often include calcium salts.

>How about when I have a baby--from conception
>to weaning that child grows lots of bone--does it all come from mine
>(yikes!) if I'm not drinking my milk?

	Yes.  It all comes from your body, but the source is not only
	your bones, but your diet as well.  Milk is probably not an
	absolute requirement, but it is an easy source of calcium.  What's
	really important, however, is that you get plenty of calcium,
	regardless of source.  Failure to do this may jeopardize your
	health and that of your baby.

>If protein leaches calcium from
>the bones, is that true of all protein, or just animal protein?

	Protein does not, in and of itself, "leach calcium from the bones."
	High protein intake tends to increase calcium excretion in the urine.
	This excreted calcium is taken from the blood.   The body requires 
	a fairly delicate balance of calcium which is transported by the 
	blood.  If the blood level of the mineral is too low, the body will 
	draw upon its reserve stores, the bones, and seek to raise the blood 
	levels.  When all is well, both removal and deposition of calcium 
	are ongoing processes.  It is only when removal outpaces deposition 
	that there is a potential problem; and if blood calcium is high in 
	the first place, perhaps due to increased consumption, then one 
	might reasonably expect a similar rise in urinary calcium, regardless 
	of diet.  It should be noted that this deposition and removal
	process is mediated by a variety of chemicals and hormones, one of
	which is vitamin D.

	Excessive intake of phosphorus can also cause increased urinary
	excretion, so limiting intake of such items as carbonated soft
	drinks can have a beneficial effect as well.

	It is not clear that excessive consumption of vegetable protein
	would not cause increased urinary excretion, but this is difficult
	to test, since excessive consumption of protein from vegetable
	sources is much less likely due to the decreased nutrient density
	of most plant sources.  There is, however, at least one study which 
	implicates cereal grains in bone loss, and another which mentions 
	soy protein.  My own opinion is that excessive protein consumption,
	regardless of source, will increase urinary excretion of calcium.

>How
>much protein is too much?  I mean, how much rice and beans and tofu can
>I eat each day before I have to get worried?

	If protein consumption is limited to levels recommended by the
	RDA, there should be little concern.  The problem with the American
	diet is that protein consumption often exceeds the RDA by a factor
	of two or three, especially for those whose diet is heavily meat-
	based.

>If I already have a full
>set of bones, why do I have to keep getting more calcium?  Why can't I
>just keep the bones I've got?

	As noted above, removal and deposition of calcium in the bones is
	a normal process, as is excretion of calcium in the urine.  Sufficient
	calcium must be consumed to compensate for the normal excretion.

>Am I just doomed if I don't eat kale?  [...]

	Hardly.  Calcium is a fairly common mineral and is found in many,
	many foods, although concentrations and availability for absorption
	vary widely.  Remember that ingestion isn't the only thing which
	affects the degree of mineralization in bones...exercise also has
	a notable effect, and absorption of calcium from food may be increased
	as exercise level increases.  Also, one large stalk of broccoli
	(now politically correct since Bush left office) contains abnout
	10 percent of the adult RDA.

>What about those multivitamin pills--is the
>calcium there at all worthwhile?

	Well, yes, it does get absorbed, but there's so little of it that
	it probably won't be a big factor.  This is not a conspiracy on the
	part of vitamin manufacturers, but rather a simple, pragmatic
	reality: a single day's supply of calcium in pill form would be
	more than could reasonably contained in one swallowable tablet or
	capsule.


>Since there are an awful lot of
>vertebrates in the world, there's an awful lot of bone, so it seems to
>me that calcium must be everywhere, in all the plants we eat.  After all,
>all the vertebrates and even some other critters always seem to find it.

	Yes, it's a fairly common mineral.

>So why are we worried at all?  Is it all dairy products that are harmful,
>or only fatty ones; i.e., how about skim milk?

	It is not at all clear that anything except the fat content of
	dairy products is 'harmful" to adults and children older than
	one year.  Skim milk is an excellent source of calcium, and the
	bugaboo regarding protein is a red herring, since it is total
	protein consumption which is the key factor in urinary calcium
	excretion.  If you're worried, eat fewer beans when you drink milk.
	Thinking of milk as a "food," rather than a "beverage," may help.

	I hope this helps answer some of your questions.


-Rich Young (These are not Kodak's opinions.)
Newsgroups: rec.food.veg