http://news.independent.co.uk/uk/health/story.jsp?story=349255


Is breast really best?
Some studies show that breast-feeding protects babies against asthma,
while others suggest it may actually increase the risk. So which is
right? A vitamin may hold the key, reports Oliver Gillie
06 November 2002
Breast-fed babies are more likely than bottle-fed babies to develop
asthma, a recent study concludes. But a dozen other studies have come to
various contradictory conclusions, leaving doctors, midwives and mothers
in a quandary. Human milk has evolved for human babies – so can it be
possible that breast is not always best?
The answer may lie in the content of human milk, which depends on the
mother's diet and lifestyle. Our increasingly unnatural lifestyle –
spending more time indoors or in cars, away from the sun – means that
breast milk is often deficient in vitamin D, especially in winter. A
small amount of vitamin D is taken in breakfast cereal, eggs, oily fish
and margarine, but most of it is obtained by the action of the sun on
the skin in summer. In winter the sun is not strong enough.
Extreme deficiency of vitamin D causes rickets, a disease of the bones
that was common in Britain before it became mandatory for vitamin D to
be added to food. But vitamin D also plays a key role in the maturation
of the immune system and so may be important in the prevention of asthma
and allergies.
The research findings linking asthma with baby feeding have puzzled
experts, as each new piece of research seems to contradict earlier
observations. The latest study of 1,037 children born in Dunedin, New
Zealand, found that children who were breast-fed for an average of 21
weeks were more than twice as likely to suffer from asthma at the age of
nine than children who were bottle-fed.
Dr Malcolm Sears, the lead investigator of the Dunedin study and now
professor at McMaster University, in Hamilton, Ontario, told The Lancet:
"We are absolutely not telling people not to breast-feed. There are many
good reasons for breast-feeding – we have just taken one of these away."
Professor Sears believes breast-feeding may increase the risk of asthma
because it reduces the risk of infections. This explanation is based on
the so-called "hygiene theory". Children who have older siblings, and
children who attend nurseries from an early age, suffer less from
asthma. According to the hygiene theory, they are more exposed to
infections that stimulate their immune system and make them resistant to
asthma.
Two years before the Dunedin study was published in The Lancet, a
similar study of 2,602 children born in Perth, Western Australia, was
published in the British Medical Journal, but the researchers came to
the opposite conclusion. The BMJ summarised the findings in a "key
message". It said: "Exclusive breast-feeding for at least four months is
associated with a significant reduction in the risk of asthma ... at age
six years."
So what are we to believe? Is breast best? There are at least a dozen
other studies from all over the world that have tried to answer the
question. Five have found that breast-feeding is associated with an
increased risk of asthma or wheezing, and six have found that
breast-feeding protects against asthma or wheezing. During the first two
years of life, breast-feeding protects against infections that may
trigger wheezing or asthma, and so breast-feeding protects against
asthma in the first two years of life. Even so, we are left with a
head-to-head contradiction between different studies that assessed
asthma at a later age.
Mothers who have asthma in the family, and so have an increased risk
that their children will develop the disease, are faced with a difficult
choice. Perhaps their babies will do better if they are bottle-fed.
Places where breast-fed babies have been found to suffer least from
asthma have a lot of sunshine. Perth in Western Australia, at 32 degrees
latitude, is renowned for its sunny climate; Kenya and Brazil, where
breast was also found to be best, are in the tropics. But babies born
and breast-fed in England or Dunedin, in the extreme south of the south
island of New Zealand, are more vulnerable to asthma. The mothers in
England and New Zealand may have received very little sunlight during
the final months of pregnancy and so have been deficient in vitamin D.
Britain is not only far north geographically, but it also has a cloudy
maritime climate that provides among the fewest hours of summer sun of
any industrial country in the world. For much of the British summer,
cloud obscures the sun, absorbing the ultraviolet light necessary for
the formation of vitamin D in the skin. And during six months of the
year – October to March – the sun is not strong enough to make any
vitamin D at all.
In Sweden, asthma has increased more in the north of the country, where
the summer season is shortest, than in the south, according to a study
carried out at the University of Gothenburg. Swedish children who were
born during the autumn and winter, when vitamin D reserves in the body
are at their lowest, were found to be most vulnerable to asthma. On the
other hand, in the highlands of New Guinea and in several parts of rural
Africa, asthma has been found to be rare. In urban South Africa and in
Harare, the capital of Zimbabwe, a significant percentage of children (3
to 6 per cent) have signs of asthma, whereas in nearby rural areas it is
extremely uncommon.
In Europe, children who live on farms, where they regularly play
outdoors, suffer less from asthma than do city children. In the United
States, the prevalence of asthma varies greatly from area to area but
has been found to be greatest in poor inner-city areas. Air pollution
has been blamed for the concentration of asthma in cities because it is
known to trigger asthma attacks, but air pollution also filters out
ultraviolet light, often preventing city dwellers from producing as much
vitamin D as they need. People in cities also have less exposure to
sunlight because opportunities for outdoor living are limited.
In the US, asthma has increased much faster among black people than it
has among whites. A person with a black skin has to spend up to six
times as long in the sun to produce the same amount of vitamin D as a
white-skinned person. Asthma is more frequent among the poor, but this
does not account for the dramatic increase in asthma among black people,
according to a study undertaken at Rutgers University in New Jersey.
Among higher income families, black children are almost twice as likely
to suffer from asthma as are white children, and among the lowest income
groups, 12.2 per cent of black children suffer from asthma compared with
9.6 per cent of white children.
It is only recently that scientists have begun to understand that
vitamin D plays an important part in controlling the immune system.
Vitamin D alters the production of substances called cytokines, which
are made by certain white blood cells. Cytokines are responsible for the
inflammation of tissue that occurs in allergies and asthma. However,
this knowledge of the importance of vitamin D for immunity does not yet
seem to have left the laboratory and impinged on medical practice.
Vitamin C – or fruits that are rich in vitamin C – has a beneficial
effect on lung function. Vitamin E (obtained from seeds and vegetable
oils) and beta-carotene (obtained from red and orange vegetables such as
carrots and maize) also seem to benefit lung function. The importance of
vitamin D has not yet been proved in direct trials. However, it is known
that if mothers are deficient in vitamin D, as many are, then babies too
will be deficient when they are breast-fed. Bottle feeds contain vitamin
D as a normal part of the formula, and once infants are weaned they will
obtain some vitamin D from margarine, butter and supplemented cereals.
The UK Committee on Medical Aspects of Food Policy (Coma) recommends
that lactating women should take 10 micrograms per day of additional
vitamin D – the equivalent to two teaspoons of cod-liver oil a day. This
is in order to provide for good growth of the baby's bones – but it may
also be useful in preventing asthma. In summer, mothers can get plenty
of vitamin D if they are able to sunbathe for 20 minutes a day in full
sun (10 minutes each side), but they should take care not to burn.
In the 1940s, free or subsidised vitamins, including vitamin D, were
provided along with milk and concentrated orange juice to all pregnant
and lactating women under the Welfare Foods Scheme. However, as families
have become more affluent this scheme has become progressively
restricted, so by 1971 only women whose families were on supplementary
benefit or family income supplement benefited from free Welfare Foods.
Could this be one of the reasons why asthma in children and young people
in the UK has increased by around 50 per cent over the past 30 years? 

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