B. L. LARSON AND K. E. EBNER
these data are limited, because of the lack of data on normal diets. The reasons for
a discrepancy between the limited laboratory experiments of Comaref al. (5, 6,
7,12) and the actual observed values of Kulp et al. (8,11) are not known. It
may be that such data from rats can not be extrapolated to humans and that
the limited studies with humansare in error. It is more likely, however, that the
form in which milk and milk products are consumed regulates the discrimination
factor. Lactose was the most powerful calcium and strontium absorption agent
found by Comare? al. (5, 12, 20); yet, many dairy products consumed by humans,
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centage from each source, can be calculated. Results of this calculation are
tabulated (Table 35).
The countries chosen for the calculations in Table 5 have greatly different
sources of dietary calcium. For example, people in the United States receive
82% of their dietary Sr-90 from milk products but, in fact, have the lowest level
of Sr-90 in Sunshine Units in their diet. The two extremes are the United States
and Japan. Only 10% of the calcium in the Japanese diet comes from milk products. On the basis of this calculation, the total intake of Sr-90 for Japan is about
two times that of the United States, because of the high level of cereals consumed
and, in fact, may be many times higher, since the cereal consumed is largely
rice, which has a short-root system (17).
_
It is apparent that if, by some means of adverse advertising and ignorance
on the part of the public, the calcium diet of the United States were shifted away
from milk to cereal or vegetable products the population would be increasing
the relative level of Sr-90 in their diet.
Influence of a milk diet on discrimination. The reason whya diet high in milk
products contains less Sr-90 than other foods is because of the additional discrimination factors operating in its formation. The data in Table 6 represent dietary
Sr-90 and not that finally deposited in the bone. There is evidence to indicate
that as the ratio of milk in the diet increases the discrimination against Sr-90
in the passage across the gut decreases (5, 6,7, 12, 20,21). It is known that
certain materials increase calcium absorption, and milk is noteworthy in this
regard. Comar et al. (5,12,20) have shown that specific substances, such as
lactose, lysine, and arginine, which tend to increase calcium absorption, are even
more effective in increasing strontium absorption. Thus, the normal discrimination from the diet to bone is about four, but on a milk diet may approach two
(5,6,7,12). Rather conclusive evidence on this point is available for the rat,
although the proportion of milk in the diet of these studies was much higher
than would be present in a normal human’s diet. The data concerning humans
are not so convincing. Such studies generally have involved Sr-89, and a limited
number of individuals who were hospitalized with advanced serious carcinomas;
all of these subjects did not show less discrimination against strontium on the
milk diet.
Kulp et al. (8,11) use the discrimination factor of four between diet and
bone for individuals in the United States. This value is based on the actual observed difference between the average level of Sr-90 in the diet of persons of
varying ages in the United States and the actual level found in bone (8}. Again,