366 TH E (H I NA STU DYCHART C.3: ROLE OF THE PARATHYROID HORMONE
IN THE REGULATION OF SUPERCHARGED 1,25 D.......... -
- ........
.. k:WWI--^1 ~O
must be maintained within a fairly narrow range. The 1,25 D keeps the
blood levels of calcium operating within this narrow range by moni-
toring and regulating how much calcium is absorbed from food being
digested in the intestine, how much calcium is excreted in the urine and
feces and how much is exchanged with the bone, the big supply tank
for the body's calcium. For example, if there is too much calcium in the
blood, 1,25 D becomes less active, less calcium is absorbed and more
calcium is excreted. It is a very sensitive balancing act in our bodies.
As blood calcium goes up, 1,25 D goes down, and when blood calcium
goes down, 1,25 D goes Up.10. 24 Here's the kicker: if calcium consump-
tion is unnecessarily high, it lowers the activity of the kidney enzyme
and, as a consequence, the level of 1,25 D .1. 25 In other words, routinely
consuming high-calcium diets is not in our best interests.
The blood levels of 1,25 D therefore are depressed both by consum-
ing too much animal protein and too much calcium. Animal-based
food, with its protein, depresses 1,25 D. Cow's milk, however, is high
both in protein and calcium. In fact, in one of the more extensive stud-
ies on MS that is associated with lower levels of 1,25 D, cow's milk
was found to be as important a factor as latitude mentioned earlier. 26
For example, the association of MS with latitude and sunshine shown
in Chart C.2 also is seen with animal-based foods shown in Chart
C.4.14
One could hypothesize that diseases like MS are due, at least in part,
to a lack of sunshine and lower vitamin D status. This is supported by the
observation that northern people living along coastlines (e.g., Norway