February 14, 1969

Dr. M. F. Brink

Director of Nutrition Research
Natonal Dairy Council

111 North Canal Street
Chicago, Illinois 60606

Dear Dr. Brink:

Thank you for your letter of February 7. I am enclosing some additional
material that reflects in published form the thrust of my remarks about
lactose intolerance.

I think that the main issue, and it is one that should be cleared up, is
some misunderstanding about what is meant by lactose intolerance. The
tolerance test is in fact a technique to determine whether lactose ig hydro-
lyzed in the gut, as reflected in the appearance of blood sugar after a test
meal. The term "lactose tolerance test" is, of course, borrowed from the
“glucose tolerance test" used in the diagnosis of diabetes.

I hope I have been careful, as I think I was at San Francisco, to stress
that the lactase deficiency of non-Gaucasiens is limited to adults, and
that alactasia in infants is a very rare disease in any population. I am
distressed that no reliable genetic studies have appeared so far about the
genetic etiology of adult alactasia. The racial differences are credible,
but for my own part I would still like to see firmer evidence that they
have a simple genetic basis. There are very feww cther traits which would
so consistently separate different races and even different tribes, apart
from superficial characteristics of skin color, etc.

I must disagree with you that adult alactasia can be ignored in planning
programs for the distribution of milk solids. The clinical significance

of the administration of lactose to individuals with alactasia is certainly
not very well understood, and there appears to be some anecdotal evidence
that they at least find milk distasteful. However, I certainly agree that
these facts must be kept in proper perspective and accurately understood as
having little bearing on infant nutrition.

However, I feel that even this point must be investiggted much more carefully;
if adult alactasia can have escaped our notice for so long in diverse racial
groups, we have to be leas complacent about unverified generalizations con-
cerning children, too. However, fnsofar as most such children thrive on
mother's milk, one can draw some reasonable common sense conclusions already.

Sincerely yours,

Joshua Lederberg