Japan had no dairy culture until the end of World War II. Japanese had essentially
been vegetarians for several hundred years. Cereals, soybeans, vegetables
and occasional seafood consumption met nutritional needs. Ordinary Japanese
neither drank milk nor ate dairy products. In contrast to Western people
who have been drinking milk for several hundred years, Asians only began
drinking milk 60 years ago. Cows' milk at one time may have been beneficial
for Western people, but I will show evidence for its ill effects on humans,
particularly on Japanese health. Even for Westerners, today's milk may be
harmful because dairy farming practices have changed significantly since
the 1920s or 1930s. Beginning about 80 years ago, pregnant cows and especially
those in the latter half of pregnancy have come to produce a greater proportion
of the milk that is consumed. Pregnancy increases the production of female
sex hormones, and these hormones are in the same or much higher range in
the milk from pregnant cows than in the blood of pregnant animals. Consumption
of dairy products is excessive in developed countries, a trend that probably
started in the 1940s and 1950s.* Our hypothesis is that the consumption
of cow milk and milk products causes various ill effects on human health.
We sincerely hope that you test this hypothesis.
*Sharpe RM, Skakkebaek NE. Are oestrogens involved in falling sperm counts
and disorders of the male reproductive tract? Lancet 341: 1392-95, 1993.
There are two main reasons why we think today's cows' milk
is not appropriate for humans: First, cows' milk contains estrogens and
progesterone in large quantities. Second, cows' milk contains too much
calcium, amounting to 125 milligrams per 100 milliliters, which is about
4 times more than that of breast milk.
First, I will describe modern and traditional milk production practices,
using Mongolia as a model for traditional milk. Next I will focus on the
hormone concentrations in these two types of milk. Then I will trace the
link between the increased hormones in modern milk and their ill effects
on human health.
I visited Mongolian Nomads in 1999. Cattle there behave as wild animals.
They move around freely, grazing at will. Nomads control their cows by
keeping their calves in an enclosure. After grazing, mother cows return
to the enclosure to nurse their calves. The nomad binds the mother cows
to the fence of the enclosure.
The nomad lets a calf out to suckle its motherŐs milk. While the calf
is nursing, the nomad binds the cow's hind legs.
Then, the nomad separates the calf from the mother and binds the calf
to the fence and begins to milk the cow for human use. Afterward the nomad
allows the calf to suckle milk again until it is satiated. I was told
that the cow pictured here was 14 years old and had given birth to 10
The volume of milk that was collected from this cow was 2 or 3 liters
at most. The volume of this container is about 20 liters.
Mongolian cows feed only on grass and they do not secrete milk during
the latter half of pregnancy. They get pregnant by natural mating in July
or August, and give birth to calves in April or May. The Mongolian nomads
milk their cows for only 5 or 6 months from May to October, obtaining,
at best, 5 liters of milk per day per cow.
I do not know whether modern dairy farming practices in Japan are the
same as in other developed countries. In Japan, the cow is impregnated
by artificial insemination 12 to 14 months after birth. The length of
pregnancy is 280 days, the same as in humans. After giving birth, the
cow secrets colostrum. Soon after birth the calf is separated from its
mother and the colostrum is milked by machine and given to the calf with
a feeding bottle for five days.
From the sixth day after delivery, the cow is milked every day for 300
days. Two or three months after delivery, the cow is inseminated artificially
and gets pregnant while it is proficient in milk secretion. Milking is
stopped for 60 days just before the next delivery, which is referred to
as the "dry period or days dry." The cow is slaughtered after
giving birth to 4 or 6 calves.
Cows are milked for 7 or 8 months while they are pregnant, including the
latter half of pregnancy up to the dry period. Modern genetically-improved
dairy cows are usually fed a combination of grass and concentrates (grain/protein
mixes and various by-products). They are milked during the latter half
of pregnancy, even at 220 days of gestation. One final comment on Japanese
dairy practices, the use of recombinant bovine growth hormone is legal
in Japan as it is in the US. However, it is said that dairy farmers in
Japan do not use this hormone. I do not know why nor whether this is true.
The most abundant hormone in milk is estrone sulfate. According to a 1979
study by Heap and Hamon, milk from non-pregnant cows contains 30 picograms
per milliliter estrone sulfate. The concentration rises with pregnancy
progression. It is 150 picograms in the first or second month of pregnancy,
and in the last stage of pregnancy it rises to as high as 1,000 picograms
Estrone sulfate has a high oral, estrogenic activity. Once in the body
it is converted to estrone or estradiol. That estrone sulfate has a high
oral activity can be understood by the fact that Premarin, which is marketed
for hormone replacement therapy contains naturally occurring conjugated
estrogens derived from pregnant mares.
We measured by high performance liquid chromatography the estrone levels
in Japanese commercial milk and traditional Mongolian milk. Holstein milk
was sterilized at 130 degrees Centigrade for 2 seconds and Jersey milk
at 125 degrees Centigrade for 2 seconds. The samples brought back from
Mongolia were of raw milk. Considerable amounts of estrone sulfate were
found in both Holstein and Jersey milk. The concentration in the commercial
milk was significantly higher than that in Mongolian raw milk. This finding
clearly shows that estrone sulfate is not destroyed by sterilization at
125 or 130 degrees Centigrade.
Milk contains another female sex hormone, progesterone. The concentration
is known to range from 10,000 picograms per milliliter in whole milk to
300,000 picograms per gram in butter.* That is, the concentration of progesterone
in milk is higher by a factor of 10-3 than that of estrone sulfate. We
measured the concentration in the commercial milk in Japan and the raw
Mongolian milk. The commercial whole milk had a much higher concentration
of progesterone than Mongolian milk. It is said that when a dairy cow
is pregnant, the progesterone concentration in whole milk exceeds 8 nanograms
or 8,000 picograms per milliliter. I can therefore positively state that
the commercial milk in Japan is derived predominantly from pregnant cows
and that the Mongolian milk is derived predominantly from non-pregnant
cows. Please note that the progesterone level in milk fat is much higher
than that in whole milk. Therefore butter and cream contain abundant female
sex hormones. Also, the ratio of the concentration of estrogens to progesterone
in the milk from pregnant cows resembles the ratio of estrogens to progesterone
in oral contraceptive pills. However, the absolute amounts of these hormones
are much lower in milk.
*Hartmann S, Lacorn M, Steinhart H. Natural occurrence of steroid hormones
in food. Food Chemistry 62: 7-20, 1998.
The question is whether the sex hormones in milk have biological significance
in humans. In answering this question, we performed two series of uterotrophic
tests, one with young ovariectomized rats and the other with sexually
The estrogen levels in the milk used in this study are listed on this
slide. The total estrogen content was 700 picograms per milliliter, of
which estrone conjugates, at 380 picograms per milliliter, comprised more
than half. In each experiment, 36 rats were divided equally among three
groups. Each group of 12 rats was kept on powder chow for 7 days, and
given one of three different liquids: commercial low-fat milk, artificial
milk, or artificial milk containing estrone sulfate at 100 nanograms per
milliliter. The artificial milk contained the same amount of protein,
fat, and carbohydrates as the low-fat milk.
At autopsy, the uterine weights were measured. This table shows the body
weight, uterine weight, and the ratio of uterine weight to body weight
in these ovariectomized rats. The uterine weight of rats treated with
low-fat milk was significantly greater than that of rats treated with
artificial milk. The ratio of the uterine weight to the body weight was
also significantly higher in the commercial milk-treated rats than the
artificial milk-treated rats. Both the absolute and relative values of
the uterine weights were higher in the estrone sulfate group than those
in the milk groups. But the difference between the two groups was not
This table shows the results in sexually immature rats. Estrone sulfate
at a concentration of 100 nanograms per milliliter had a more marked uterotrophic
activity than the low-fat milk. The uterine weight in the commercial milk
group was significantly higher than that of the artificial milk group.
It can be said that the uteri of immature rats are much more sensitive
to estrone sulfate than the uteri of sexually mature rats. From this study,
we conclude that commercially available milk in Japan has uterotrophic
activity in both young ovariectomized rats and sexually immature rats.
I would like to draw your attention now to the recent decline in fertility
Japan has experienced dramatic lifestyle changes since World War II. In
1954 a law was enacted making it compulsory for children to drink 200
milliliters of milk at every school lunch. School children are not allowed
to go out until they finish their milk. Since the enactment of The School
Lunch Law, consumption of milk and dairy products increased 20-fold
As a natural consequence of the School Lunch Law, the consumption of milk
and dairy products by prepubertal boys and girls is quite high in Japan.
The average dairy consumption in this age group reaches 320 grams per
day (approximately 11 ounces or 325 milliliters).
A boy who drinks 300 milliliters of milk a day is calculated to take 100
nanograms estrone sulfate into his body everyday. Some children actually
drink 1 liter of milk a day because their parents encourage them to quench
their thirst with milk instead of water. One liter of milk contains 370
nanograms of estrone sulfate alone. According to Andersson and Skakkebaek
of Denmark,* the daily production of estradiol in prepubertal boys is
in the range of 40 to 100 nanograms. The question that naturally arises
is whether the several hundred nanograms of estrone sulfate in commercial
milk has any adverse effects on the sexual maturity of prepubertal boys.
No clear answer to this question is available at present.
*Andersson AM, Skakkebaek NE. Exposure to exogenous estrogens in food:
possible impact on human development and health. European Journal of Endocrinology
140: 477-85, 1999.
The population size of Japan is shrinking. The total fertility rate, that
is, the average number of children born to each woman in her lifetime
was 2.16 in 1970. It started declining in 1974, and has continued to decline,
recording the lowest level, 1.25 in 2005. According to economists and
sociologists, this decline is attributable to non-marriage and late marriage,
which now prevails among the younger generation in Japan. In principle
I agree with this view.
However, in Japan one in seven couples are infertile and about 460,000
couples now receive infertility treatment. In 1973, 2.8 million pregnancies
occurred. But 30 years later in 2004, the number of pregnancies declined
by one half to 1.4 million. Use of oral contraceptives was not approved
by The Japan Ministry of Health and Welfare until 1999. As in the United
States, access to oral contraceptives in Japan is restricted to prescription
by a gynecologist or obstetrician. I am therefore inclined to consider
that the decline in fertility in Japan is partly caused by a decrease
in male reproductive ability.
Semen quality has so far been said to be the lowest in Denmark. However,
according to a recent study performed in Japan, semen quality of Japanese
men in Kawasaki and Yokohama was worse than Danish men in Copenhagen.
It is of importance to note that in the past 50 years, the incidence of
testis cancer has increased while semen quality has decreased worldwide.
Dr. Skakkebaek of Denmark has proposed the testicular dysgenesis syndrome
hypothesis that suggests that the incidences of hypospadia, cryptorchidism,
impaired spermatogenesis, and testis cancer are related to perinatal exposures
to environmental endocrine disruptors.
To further investigate the recent increase in testicular cancer, we examined
the relationship between food consumption and testis cancer incidence
in 42 countries.* In almost all countries, the highest incidence of testis
cancer was found between ages 20 to 39 years. Hence, the incidence in
1990 was correlated with food consumption between 1961 and 1970. Among
food items, cheese was most closely correlated with testis cancer incidence,
followed by milk and animal fats.
*Ganmaa D, Li XM, Wang J, Qin LQ, Wang PY, Sato A. Incidence and mortality
of testicular and prostatic cancers in relation to world dietary practices.
International Journal of Cancer 98: 262-267, 2002.
Stepwise-multiple regression analysis identified the combination of cheese
and milk as the factor contributing most to the incidence of testis cancer.
We hypothesize that sex hormones or some other ingredients in cheese or
some particular processes in cheese production may have adverse effects
on testicular development.
The association of testis cancer incidence with cheese consumption shows
a distinct difference between the two Scandinavian countries, Denmark
and Finland. Both testis cancer incidence and cheese consumption are high
in Denmark, but both are low in Finland. We were eager to know why the
opposite occurs in these two dairy consuming countries.
This figure shows the yearly consumption of cheese in Denmark and Finland
from 1961 to 1990. In the 1960s and 1970s, the consumption of cheese was
much higher in Denmark than in Finland. However, the consumption in Finland
increased rapidly in the 1980s and is reaching almost the same level as
that in Denmark in more recent years. We suspect that testis cancer incidence
in Finland is increasing now as well, and will catch up to the incidence
in Denmark in 20 or 30 years.
I will now address the topic of hormone-dependent cancers, prostate cancer
in men and breast cancer in women.
Prostate cancer incidence is much lower in Japan than in Western countries.
Nevertheless, prostate cancer mortality increased almost linearly, about
25-fold over the last 50 years.
Our ecological study found that both incidence and mortality of prostate
cancer are most closely correlated with the consumption of milk.
Multiple-regression analysis identified the consumption of milk and cheese
as the factor most contributing to both the incidence and mortality of
Although Japan now has the most rapidly increasing rate of prostate cancer
incidence in the world, the incidence in Japan is less than one-tenth
that in the United States. What causes this big difference?
I am sure that this difference can be explained by the difference in milk
consumption between the two countries. This graph compares daily milk
and dairy product consumption, excluding butter. Americans consume more
than 1,000 grams of milk and dairy products a day, while Japanese consume
about 300 grams a day. The consumption in the United States is about 4
times higher than that in Japan.
With respect to breast cancer, our ecological study revealed that the
food that is most highly associated with the incidence and mortality of
the cancer is milk and dairy products.
Multiple-regression analysis revealed that the most significant contributor
to breast cancer incidence is meat, while the most significant contributor
to breast cancer mortality is milk and cheese consumption.
Breast cancer incidence in the US is much higher
than that in Japan.
I am sure that, as in the case of prostate cancer, this big difference
can be explained by the difference in milk consumption between Japan and
the U.S. Epidemiological findings have not always evidenced this association
between incidence of breast cancer and consumption of milk and dairy products.
However, in nutritional epidemiology precise evaluations of individual
consumption of dairy products is very difficult because dairy products
are used in a variety of Western foods, including bread, ice cream, chocolate,
cake, and some cookies. In Western countries dairy consumption is a life
long dietary habit of most people. It may be difficult to find a group
of women who completely avoid dairy consumption, except for vegans. The
problem would easily be solved if epidemiologists compare the breast cancer
incidence between strict vegans and lacto-ovo vegetarians.
We assessed the effects of commercial low-fat milk on the development
of DMBA-induced mammary tumors in rats. The details have been described
in the International Journal of Cancer.
DMBA or 7,12-dimethylbenzanthracene is a chemical carcinogen. When given
to rats, it causes mammary tumors. The development of mammary tumors is
hormone-dependent and has frequently been used as a model for human breast
I will outline the experimental design. Rats of six weeks of age were
given a single oral dose of DMBA. The animals were then divided into four
groups and kept on different dietary regimens. Low-fat milk was the experimental
group; artificial milk served as the control group; estrone sulfate as
the positive control group; and water as the negative control group. Rats
were palpated weekly to monitor tumor development. 20 weeks after DMBA
administration, rats were autopsied.
As you can see from this slide, there was no significant difference in
body weight between the commercial milk group and the artificial milk
This slide shows the cumulative incidence of mammary tumors. Please note
the difference between the commercial milk and the artificial milk groups.
The incidence was significantly higher in the commercial milk group than
in the artificial milk group.
This slide shows the cumulative number of mammary tumors. The number of
tumors was also greater in the commercial milk group than in the artificial
milk group. Estrone sulfate, too, significantly promoted the development
Finally, the size of the tumors that developed in the commercial milk
group was greater than those in the artificial milk group.
This table shows the serum levels of estrone and IGF-1 at the end of the
experiment. Commercial low-fat milk increased the level of IGF-1 in addition
to the estrone level. Although estrone sulfate given orally increased
the serum level of estrone, this hormone alone did not affect the level
We conclude that commercially available low-fat milk promotes the development
of DMBA-induced mammary tumors in rats. The degree of the promotion is
almost comparable to that of 100 nanograms per milliliter of estrone sulfate.
The high estrogen content in milk may be responsible for the promotional
effects, acting in concert with other hormones such as IGF-1.
Before I conclude my talk, I will briefly update you on the problem of
Bovine Spongiform Encephalopathy, or BSE in Japan.
By September 28th of this year (2006), 29 cattle had been diagnosed with
BSE. Of them, 28 were Holstein dairy cows. It is certain that the BSE
outbreak in Japan is related to todayŐs dairy farming practices, but the
details remain unknown.
We have a proposal for dairy farmers all over the world. Consumers have
demonstrated their willingness to pay higher prices for organic milk.
We feel that milk from non-pregnant cows would also be marketable at premium
In conclusion, you may feel skeptical that milk is harmful to human health.
You may say that you have been drinking milk and eating dairy products
for several hundred years without any apparent harm. I would like you
to understand that today's milk is vastly different from the milk your
ancestors consumed 80 years ago.
We thank Ms. Kris Demko for revising our manuscript.