The China Study by Thomas Campbell

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activity. Within seconds, parathyroid hormone manages how much 1,25
D there will be at each time and place. Parathyroid hormone also acts as
a conductor at several other places in this network, as shown by the sev-
eral arrows. By being aware of the role of each player in its "orchestra,"
it coordinates, controls and finely tunes these reactions as a conductor
would a symphony orchestra.
Under optimal conditions, sunshine exposure alone can supply all
the vitamin D that we need to produce the all-important 1,25 D at the
right time. Even the elderly, who are not able to produce as much vita-
min D from sunshine, have nothing to worry about if there is enough
sunshineY How much is "enough"? If you know how much sunshine
causes a slight redness of your skin, then one-fourth of this amount,
provided two to three times per week, is more than adequate to meet
our vitamin D needs and to store some in our liver and body fatY If
your skin becomes slightly red after about thirty minutes in the sun,
then ten minutes, three times per week will be enough exposure to get
plenty of vitamin D.
When and if we don't get enough sunshine, it may be helpful to con-
sume vitamin D from our diets. Almost all of the vitamin D found in our
diet has been artificially added to foods like milk and breakfast cereals.
Along with vitamin supplements, this amount of vitamin D can be quite
significant and, under certain circumstances, there is some evidence
that this practice may be beneficial. 18-21
In this scheme, sunshine and parathyroid hormone work together in
a marvelously coordinated way to keep this system running smoothly,
both in filling our vitamin D tank and in helping to produce from mo-
ment to moment the exact amount of 1,25 D that we need. When it
comes to getting sufficient sunshine or getting vitamin D in food, taking
light from the sun makes far more sense.


There are several studies now showing that if 1,25 D remains at con-
sistently low levels, the risk of several diseases increases. So then the
question is: what causes low levels of 1,25 D? Animal protein-contain-
ing foods cause a significant decrease in 1,25 D.22 These proteins create
an acidic environment in the blood that blocks the kidney enzyme from
producing this very important metabolite.^23
A second factor that influences this process is calcium. Calcium in
our blood is crucial for optimum muscle and nerve functioning, and it

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