Since the birth of the People’s Republic in 1949, China has experienced
a revolution in public health. In one of the great medical success stories
of our century, the Chinese have largely won the battle against malnutrition,
and infectious and parasitic diseases. At the death rates of the 1940s,
about half the children born in China could expect to die before reaching
middle age. But at current death rates, more than 90 per cent can now expect
to survive to middle age, as in the West, and China has achieved this ‘epidemiological
transition’ in less than half th time it took Britain.
Now, the chief causes of premature death are the ‘chronic’ diseases
of middle age – primarily stroke, emphysema, hepatitis-B-related disease
(liver cancer or cirrhosis), and, last but not least, diseases linked to
tobacco. So, as the children of Mao’s baby boom reach middle age, China
will inevitably suffer an explosion in the number of premature deaths from
chronic disease. But more than demographic change is at work. Deaths from
lung cancer are increasing rapidly because cigarette smoking has, relatively
recently, become widespread in China, and by the late 2020s almost a million
a year may die from this disease alone. Smoking will kill even more from
other diseases besides lung cancer. And, as the country grows richer, so
too might its diet move closer to the Western ‘norm’, bringing heart disease
and diabetes to millions.
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So China is now faced with an enormous challenge – that of widening
the health priorities for one-fith of the world’s population to include
the prevention of chronic disease, while still completing its first health
care revolution. ‘Put prevention first’ was China’s health slogan in the
early days of the Republic, when most deaths were from communicable diseases.
But, as China’s health minister Chen Min-Zhang points out, the slogan applies
equally well to the remaining chronic diseases that now account for many
of the premature deaths in China. Indeed, prevention is even more important
because for most of the chronic diseases there is no real cure.
The Chinese government is now considering various anti-tobacco measures,
ranging from restrictions on tar levels and advertising, to labelling cigarettes
with health warnings and providing smoke-free areas. Officials also acknowledge
that the notion of introducing a Western-style agriculture that is heavily
reliant on livestock is neither practicable nor medically desirable for
the Chinese people. These far-sighted policies have their beginnings, in
large part, in a huge nationwide survey of the causes of all deaths in the
whole of China between 1973 and 1975. Some 600,000 people worked on the
survey, which covered 96 per cent of the population – then some 850,000,000
people. Authorised by Premier Zhou En-Lai in the last year of his life,
when he himself had bladder cancer, it is one of the largest epidemiological
studies ever done.
It was a visionary move. Zhou En-Lai commissioned the study because
‘the first thing in battle is to know where your enemy is’ – or, in this
case, where particular types of cancers are occurring. The result was the
Chinese Cancer Atlas, published in 1980. It maps the geography of each main
type of malignant disease, and reveals huge and intriguing variations from
one part of China to another in each of the major types of cancer. Regions
just a few hundred miles apart sometimes show a tenfold difference in the
mortality rates from liver cancer, for instance. Indeed, every type of cancer
that is common in one part of China is much less common in some other part.
This suggests that most of the risk could be avoided, if only we could understand
the main reasons for these huge differences.
The Chinese Cancer Atlas has inspired a wide range of further studies
into the causes and correlates of chronic disease in China, many in collaboration
with researchers in the US, France or Britain. The latest study, and one
of the largest, is described in a weighty monograph published simultaneously
this week in China and in the West*. Entitled Diet, Life-style, and Mortaility
in China, it describes 65 countries (3 per cent of the total) scattered
all over the populated parts of the Chinese countryside. It is the result
of a fertile collaboration over the past 10 years between two Chinese researchers,
Chen Junshi of the Academy of Preventive Medicine in Beijing, and Li Junyao
of the China Cancer Institute in Beijing, one American, Colin Campbell of
Cornell University, one Briton, Richard Peto of the ICRF Cancer Studies
Unit at the University of Oxford, and almost a hundred other colleagues
in laboratories around the world.
The study describes the geographic variation across China not only for
various cancers but also, for the first time, for other major causes of
death (such as stroke, hypertensive heart disease, chronic lung disease
and tuberculosis), using data from the original survey of 1973-75. What
makes this new study so interesting is that, based on special surveys in
1983 and 1984 in 65 chosen counties, the researchers have tried to describe
the way people live as well as how they die. One aim is to correlate the
two, but the wider goal is simply descriptive – to provide information that
will suggest new hypotheses and form the groundwork for further research.
To chart the geography of lifestyle, diet and body biochemistry, teams
of researchers interviewed thousands of people, and collected endless samples
of blood, urine and food from all over the country. The heart of the monograph
is 367 maps, one for each aspect of death or of life that was studied. These
maps illustrate the great variation between different counties not only
in the deaths attributed to 82 specific diseases, but also in 150 aspects
of the Chinese lifestyle – smoking, drinking, eating and reproduction –
and in 135 biochemical attributes of blood and urine.
The organisation required to collect thousands of samples of blood,
urine and food, store them safely, and eventually fly them for analysis
to laboratories in Beijing and all around the world would be substantial
even in the world’s richest nations. To have accomplished this in a developing
country is an astounding achievment. The survey team from the Institute
of Nutrition and Food Hygiene in Beijing was well organised and entirely
committed to the task – which involved obtaining blood and urine samples
from people living in 130 villages scattered widely across China (including
‘an oasis village near the Great Gobi Desert and a nomadic group on the
Soviet border that required four days of travel over severe terrain from
the nearest airport’, says Campbell).
Chen Junshi at the nutrition institute was the linchpin, backed by provincial
health survey teams all over China and scores of analytical laboratories
in Beijing and all around the world that carried out assays free of charge.
Chen met Campbell during an eight-month sabbatical visit to the Cornell
Division of Nutritional Sciences in 1980, just as the Chinese Cancer Atlas
was being published, and the striking heterogeneity of some of the cancer
rates in the atlas led them to initiate what was originally thought of as
a study just of nutrition and cancer. But Li, in Beijing, arranged for information
on other causes of death to be provided, and Peto, in the Oxford ICRF cancer
unit, devised practicable methods for blood samples to be analysed for dozens
of different characteristics.
To save money, the team adopted a novel approach: pooling blood samples
from particular groups of people – say, males in a particular village –
and then doing on that pooled blood sample many different assays. This approach
reduced the number of laboratory analyses that had to be done to work out
the mean values in each country, but still allowed statistical checks on
the quality and consistency of the data.
The study was incredibly good value for money. With only $2 million,
over seven years, in hard cash, mostly from the National Institutes of Health,
plus 600 person-year of labour, mostly contributed by the Chinese government,
the team achieved what could probably not have been done anywhere else.
Three other people, Feng Zulin in Beijing, Linda Youngman at Cornell and
Jillian Boreham at the Oxford ICRF unit then spent years coordinating assays
and data management, as well as nursing the monograph text through the labour
of publication in side-by-side English and Chinese.
The amount of data is staggering – as well as the average results for
the men and for the women in each village, there are some 100,000 between-county
correlation coefficients to wade through and weigh up, for a start. Several
positive correlations between the findings in different counties probably
do reflect real cause-and-effect relationships – for example, stomach cancer
with chronic infection by gastric bacterium, Helicobacter pylorum; liver
cancer with chronic infection by the hepatitis B virus; lung cancer with
cigarettes; intestinal cancer with chornic intestinal infection by Schistosomiasis
japonicum (‘snail fever’); oesophagus cancer with low vitamin C (from fresh
fruit and vegetables); stroke with salt consumption; and heart muscle wastage
(‘Keshan disease’) with severe selenium deficiency.
But the authors deliberately draw no formal conclusions, perhaps partly
because they still differ somewhat in their philosophical perspectives.
Peto rather distrusts many of the geographic correlations, and particulary
distrusts multiple ones; he argues that the study’s strength lies in its
ability to inspire further, more tightly defined studies (some of which
are already in progress) that can test particular ideas. Campbell, while
agreeing on the need for additional studies, thinks that we may nevertheless
be able to draw quite subtle inferences from multiple correlations between
many interacting factors. ‘The present series of surveys may offer a unique
opportunity to consider causes of human cancer as they realistically exist
within the complex human environment,’ he says. ‘The complexity of both
diet and disease must be addressed at every opportunity.’
Campbell is attracted to the notion that ‘the lowest risk for cancer
is generated by the consumption of a variety of fresh plant products’ –
what he calls the ‘plant nutrient hypothesis’. The first step towards cancer,
he argues, is probably the result of exposure to something in the environment,
such as hepatitis B virus, tobacco, aflatoxin or nitrosamines. But Campbell
emphasises that nutrients can then modulate in various ways the subsequent
development of the cancerous cells, and argues that a diet low in a variety
of fresh plant foods generally increases the risk that a pathological cancer
will actually emerge. If this is true, then the right diet might slow or
even reverse pre-clinical stages of the cancer process.
East v West
The comparison of China and the West is particularly fascinating, says
Campbell, because ‘for most nutrients and many metabolic indicators, Chinese
and Western values would appear to be at opposite ends of a spectrum’. The
survey found, for instance, that fat generally accounted for only 6 to 25
per cent of dietary calories (the average being 15 per cent). Yet even the
top of this range falls below the vast majority of Western intakes: in Britain,
for example, the average is often about 45 per cent, and even a ‘low-fat’
British diet might average about 30 per cent calories from fat. Compared
with Americans, Chinese people eat on average 22 per cent less protein and
64 per cent less fat, 75 per cent more soluble carbohydrate and 157 per
cent more fibre.
The variety of ways of living within China, ranging from the nomadic
herders of the Inner Mongolia Region to the suburban dwellers of Shanghai,
also makes the survey especially interesting. Rice is the staple food of
southern China, for instance, but in the northern half of this vast country
people eat mainly wheat, corn or millet. In the weighed diet survey, salt
intake ranged from 2 grams a day to a whopping 30 grams, with an average
of 15 grams (Britons consume 8 grams a day on average, and are urged to
reduce this to below 5.) Most Chinese never eat milk or dairy products,
but the nomadic herders of the northwestern county of Tuoli obtain more
than half their calories and three-quarters of their protein from this source.
‘Epidemiologists need to be able to study large, persistent differences
between the ways in which different people live and the ways in which they
die,’ says Peto; China – vast, heterogeneous – is an ideal laboratory.
The data amassed about the Chinese way of life underline the healthfulness
of a diet rich in plant foods, says Campbell. For instance, the study seems
to refute worries in the West that diets high in fibre might seriously interfere
with the ability to absorb minerals such as iron. The Chinese with the highest
intake of fibre also had the most iron in their blood. Even Chinese people
who ate no meat showed no sign of anaemia, nor, according to other evidence,
did they suffer inordinately from osteoporosis despite a lack of calcium-rich
dairy products.
One of the most striking diet-related differences between East and West,
however, is the level of cholesteral in the blood. A third of all deaths
in middle age in Britain are from cholesterol-related diseases, many of
which are the result of a diet rich in saturated animal fats. In Britain
an average of between 40 and 45 per cent of dietary energy comes from fat,
but in rural China in 1983 only 15 per cent did so, and virtually all that
came from plant fats, not animal or dairy fats.
Diet for a healthy heart
As a result of this largely vegetarian, almost vegan diet in rural China,
cholesterol levels are, by Western standards, extraordinarily low, and coronary
heart disease is rarely recorded as a cause of death. ‘The Chinese experience
shows that most of Western coronary heart disease is unnecessary,’ says
Peto.
Interestingly, prospective studies by Chen Zhengming and his colleagues
in Shanghai, in collaboration with the Oxford unit, have shown that there
is still, even without China, a direct relationship between blood cholesterol
level and the relative risk of coronary heart disease – the lower the levels
the lower the risk, with no sign of a threshold. So as far as cholesterol
levels are concerned, ‘there is no such thing as a really normal Englishman’,
says Peto. (Importantly, the Shanghai study also tends to counter the notion
that low levels of cholesterol could predispose to stroke).
Will the Chinese diet begin to alter along Western lines? So far, Western
hamburger chains and the like have made a few inroads, and the findings
of this and other surveys may help to create the political will to maintain
some of the good aspects of the traditional Chinese diet towards not an
American but perhaps a Japanese diet,’ says Campbell – that is, not towards
sugar and animal fat but towards fish and plant protein.
Perhaps, however, the most immediately important result of the study
is that it has helped to draw the attention of the Chinese authorities to
the vast epidemic of chronic disease and death that tobacco carries in its
wake. Peto has made great efforts to spread the word. ‘It has been important
for everyone to understand that the predicted mortality from tobacco is
real,’ he says. ‘In the 1950s, one popular slogan in China was ‘Food, shelter
and cigarettes for everybody’ – that is, essentials and a few luxuries.
If you were a revolutionary in the 1930s the least of your worries was that
you might die in middle age of smoking.’ But things have changed. China
is at the beginning of a vast epidemic of smoking-related disease: ‘As far
as male cigarette smoking is concerned, China is now where the US was in
1945, and the pattern of rapidly increasing lung cancer death is going to
be much the same,’ says Peto. By the mid 1980s, male lung cancer had overtaken
other cancers in China’s cities.
Last year, the Chinese consumed almost a third of the world’s cigarettes
– with consumption having risen from 500 billion cigarettes in 1978 to 1600
billion just over a decade later. The rapid increase has taken China up
to the worst male smoking rates for the US and Britain. In Britain and North
America, however, cigarette smoking has decreased, and in the US only one-third
of the men now smoke; in China, two-thirds do. ‘We can learn from China
about what low cholesterol can do,’ says Peto, ‘and China can learn from
our experience with tobacco what cigarettes are going to do.’
Current trends suggest that there will be a rapid rise in the incidence
of lung cancer among men in China – from 30,000 in 1975 to 900,000 in 2025.
By that time, most men will have smoked cigarettes throughout adult life,
(and the surveys of Weng Xin-Zhi, one of the first to warn seriously against
smoking in China, show that in Beijing young women are now also beginning
to do so). Demographic changes – a fourfold increase in the number of men
old enough to be at risk of lung cancer – will be responsible for a fourfold
increase in lung cancer numbers, while medical change – the delayed effects
of the large increase in smoking – will be responsible for about a sevenfold
increase. Chairman Mao did not believe in birth control, and there are now
420 million Chinese under 20. On present smoking patterns, about 150 or
200 million of these young people will become adult smokers and about a
quarter or a third of those who smoke cigarettes regularly are eventually
killed by the habit. So in total about 50 million of those now aged under
20 in China will eventually be killed by tobacco.
At the moment, chronic obstructive pulmonary disease (COPD), also know
as emphysema, is, with stroke, the commonest cause of death in middle age
in China. No one really knows why it is so common – although air pollution
from cooking over coal-fired open pots could be important. Smoking is a
cause of most COPD in the West, but in China women die of COPD as often
as men, even though few women smoke. ‘What will smoking do on top of that
high background?’ says Peto. ‘It will certainly produce an enormous amount
of severe, permanent COPD disability, and might produce even more deaths
from COPD than from lung cancer.’
We need to know much more about current and future smoking-related mortality
in China. Three major studies will help to fill the gaps in our knowledge.
One now underway, again in a collaboration between the Beijing Cancer Institute,
the Beijing Nutrition Institute, Cornell University and the ICRF unit at
Oxford, involves a retrospective assessment of the smoking habits of 600,000
married people who died between 1986 and 1988, by interviewing each of the
surviving spouses. (Surviving spouses can also act as controls for the deaths
of married people.) Another, in collaboration between the Shanghai Tumour
Institute and the US National Cancer Institute, is a large local prospective
study of smoking in central and suburban Shanghai and in the country near
the city. The third, organised by the Chinese Academy of Preventive Medicine
with funds from the World Bank, is a very large, nationwide prospective
study of the smoking habits and other characteristics of half a million
Chinese people, with follow-up to record the causes of all their deaths
every five years for at least 20 years thereafter. ‘Such studies will monitor
first the current state, and then the evolution, of this great epidemic,’
says Peto.
All sorts of other studies are also planned or in progress, direct or
indirect offshoots of the original cancer atlas or the present survey of
65 counties .
Chen Min-Zhang, the Minister of Public Health, has said that when the
health priorities become clear, China can act faster than other countries.
But recent structural changes in China may make this more difficult. Communal
health care may be replaced by ‘self-financing’ clinics with no economic
interest in the prevention of disease or in the treatment or vaccination
of those who cannot pay. Even the World Bank, in its 1990 report on the
Chinese health sector, emphasises tha incentive-based systems that can increase
overall cost-efficiency in other sectors of the Chinese economy may decrease
it when it comes to the control of disease. This is true for communicable
diseases, but it is even more true for non-communicable diseases, where
cure is difficult and prevention may require social change.
But in the long run, Premier Zhou En-Lai’s nationwide mortality survey
probably did mark the beginning of a second stage in China that will help
to control premature death from non-communicable diseases. Yet to achieve
this goal China will need more descriptive studies such as Diet, Life-style
and Mortality, more specific studies of individual causes of death and the
establishment of a strong tradition of large, simple, properly randomised
trials that can assess treatments reliability. It will also depend on finding
ways to ensure a proper balance between the prevention and treatment of
disease, whatever economic structures China ultimately adopts.
* * *
Work in progress: A growing tradition of strong research
The original Chinese Cancer Atlas and, more recently, the study of disease
and lifestyle in China have already inspired scores of further specialised,
in-depth studies, involving international teams of scientists and doctors.
Below are just a few projects now underway.
Food and cancer Li Junyao of the China Cancer Institute in Beijing is
collaborating with the American National Cancer Institute in a vitamin intervention
trial involving more than 30,000 people. The idea is to see whether a combination
of vitamins might help to slow or reverse precancerous lesions in the oesophagus.
The WHO International Agency for Research on Cancer has also worked with
the Chinese Cancer Institute in a similar vitamin trial, and with Chen Junshi
at the Nutrition Institute in Beijing on studies of precursors of nitrosamines
in the diet.
Bones and dairy products Workers at Cornell University are collaborating
with Chinese researchers in a study to see whether there really is no difference
between the incidence of osteoporosis in Inner Mongolia, where nomadic herders
consume a diet rich in dairy products, and in another region of China where
no one eats dairy products.
Viruses, vaccines and cancer Researchers at the cancer institutes of
Beijing and Qidong, with scientists from the WHO and the ICRF in Britain,
are conducting a large, randomised trial of vaccination against hepatitis
B virus for 60,000 infants in Qidong county. The idea is to find out what,
if any, vaccination regimen is most effective in preventing liver cancer
40 years later.
Stroke, salt and high blood pressure Prospective studies have already
shown that stroke in China is often driven by hypertension. High blood pressure
may be common in China partly because salt consumption is so high. More
information on how diet affects blood pressure is needed, but working to
reduce salt in the storage and preparation of food may help to lower the
incidence of stroke in the long run.
Meanwhile, randomised trials of 7,000 stroke patients are getting underway
in a nationwide network of hospitals coordinated through the Fu Wai Hospital
in Beijing. The goal is to find out whether drugs that lower blood pressure
reduce the risk of having a further stroke, even if the patient has blood
pressure in the supposedly ‘normal’ range.
Scores of other studies are also planned or in progress, including a
complete repetition by Chen, Campbell, Li and Peto of the entire 65-county
survey.
* Diet, Life-style, and Mortality in China, a study of the characteristics
of 65 Chinese counties, by Chen Junshi, T Colin Campbell, Li Junyao and
Richard Peto, is jointly published by Oxford University Press (95 Pounds
Pounds), Cornell University Press and the People’s Medical Publishing House,
Beijing, 1990.